California Agriculture

APRIL-JUNE 2005 ° VOLUME 59 NUMBER 2 California Agriculture

Kearney at 40: Research blooms in the Valley

University of California | Division of Agriculture and Natural Resources | Research in Agricultural, Natural and Human Resources

40 COVER: Orchard-systems research conducted at KREC on peaches (shown in bloom) and other tree fruits has reduced labor costs and improved grower proﬁtability (see pages 75, 80). Cover and table of contents photos by Jack Kelly Clark. Kearney Research and Extension Center News departments Research articles

52 Letters 65 Blueberry research launches exciting new 53 Editorial overview California specialty crop Collaboration fosters Kearney Jimenez et al. scientiﬁc achievements New cultivars are productive in the semiarid Central Valley, but initial soil preparation 56 Introduction and establishment costs are high. Agricultural innovation marks 40 years at Kearney 70 The future of California raisins Legendary “mother” pistachio is drying on the vine tree to be retired Peacock, Swanson KREC researchers developed a low-cost 62 Research updates method of drying raisins on the vine; yields “Farm to palate” postharvest research equaled those of traditional tray-drying for ensures high-quality produce 4 consecutive years.

UC nematologists battle Orchard-system configurations tiny underground pests 75 increase efficiency, improve 4064 Science brief profits in peaches and nectarines Lygus study validates Day, DeJong, Johnson treatment thresholds Higher-density planting systems, coupled with pruning techniques that enhance light interception, provide economic benefits for orchardists.

Editor’s note 80 Labor costs may be reduced . . . We gratefully acknowledge the efforts of Research yields size-controlling those who contributed to this special issue rootstocks for peach production on the 40th anniversary of the UC Kearney DeJong et al. Research and Extension Center (KREC): After 8 years in the orchard, trees on ﬁve David A. Grantz, Kearney Agricultural experimental rootstocks had positive results; Center Director, and Frederick H. Swanson, three have been made available to growers. KREC Director, who served as co-chairs; California Agriculture Associate Editors 84 Methyl bromide alternatives . . . Kevin R. Day, Steven A. Fennimore, Debo- Soil solarization provides weed rah A. Golino, Mark E. Grismer, John Letey control for limited-resource and and Carole Lovatt, who oversaw peer re- organic growers in warmer cli- view of the manuscripts; Jack Kelly Clark, mates Principal Photographer with ANR Com- Stapleton et al. munication Services, for original photog- For small-acreage specialty crops, solariza- raphy and digital color correction; Photo tion can be much less expensive than methyl Assistant John Stumbos, for compiling the bromide fumigation, with comparable yields and weed control. images and writing captions; and KREC for providing funding to make this double issue (the largest in California Agriculture history) possible. Signs of the times

California Agriculture

Since its dedication on May 26, 1965, the laboratories, administrative offices, meeting Peer-reviewed research and news published place commonly known as “Kearney” has rooms, dormitories and an airstrip. The “UC by the Division of Agriculture and undergone numerous name changes. Today, Kearney Agricultural Center” (KAC) is an aca- Natural Resources, University of California the “UC Kearney Research and Extension demic unit, akin to a campus, which includes VOLUME 59, NUMBER 2 Center” (KREC) refers to the entire 330-acre scientists in residence and their staff. Far Executive editor: Janet White facility, including field sites, greenhouses, left, Fred Swanson. Managing editor: Janet Byron Art director: Davis Krauter California Agriculture 1111 Franklin St., 6th floor Oakland, CA 94607-5200 Phone: (510) 987-0044; Fax: (510) 465-2659 90 Mulches reduce aphid-borne 115 Conventional and molecular [email protected] viruses and whiteflies in cantaloupe assays aid diagnosis of crop dis- http://CaliforniaAgriculture.ucop.edu eases and fungicide resistance California Agriculture (ISSN 0008-0845) is published quarterly and mailed at period- Summers, Mitchell, Stapleton icals postage rates at Oakland, CA and additional mailing offices. Postmaster: Send Plastic and wheat straw mulch decreased Michailides et al. change of address "Form 3579" to California Agriculture at the above address. RATES: Subscriptions free upon request in U.S.; $24/year outside the U.S. Af- aphid-borne viruses and whitefly in canta- Molecular assays offer the possibility of ter publication, the single copy price is $5.00. Orders must be accompanied by loupe, increasing yields and late-season fruit much faster, more reliable plant disease payment. Payment may be by check or international money order in U.S. funds payable to UC Regents. MasterCard/Visa accepted; requests require signature size without pesticides. tests, and already can supplement conven- and card expiration date. Please include complete address. tional techniques. Articles published herein may be reprinted, provided no advertisement for a commercial product is implied or imprinted. Please credit California Agriculture, 95 Large bugs damage pistachio nuts University of California, citing volume and number, or complete date of issue, most severely during midseason 124 Deep vadose zone hydrology followed by inclusive page numbers. Indicate ©[[date]] The Regents of the Uni- versity of California. Photographs may not be reprinted without permission. Daane et al. demonstrates fate of nitrate in UC prohibits discrimination against or harassment of any person on the basis eastern San Joaquin Valley of race, color, national origin, religion, sex, gender identity, pregnancy (includ- Large bugs cause the most damage to pista- ing childbirth and medical conditions related to pregnancy and childbirth), chios in June and July, after the fruit load is Harter et al. physical or mental disability, medical condition (cancer-related or genetic characteristics), ancestry, marital status, age, sexual orientation, citizenship, or sta- set but before shells harden. Analysis of 52-foot cores under a former tus as a covered veteran (special disabled veteran, recently separated veteran, Vietnam-era veteran or any other veteran who served on active duty during orchard showed heterogeneous water flow a war or in a campaign or expedition for which a campaign badge has been 103 Early harvest delays berry skin patterns and preferential flow paths for wa- authorized) in any of its programs or activities. University Policy is intended to terborne pollutants. be consistent with the provisions of applicable State and Federal laws. Inquiries browning of ‘Princess’ table grapes regarding the University's nondiscrimination policies may be directed to the Vial, Crisosto, Crisosto Affirmative Action/Staff Personnel Services Director, University of California, 133 Weighing lysimeters aid Agriculture and Natural Resources, 300 Lakeside Dr., 6th Floor, Oakland, CA Skin browning in ‘Princess’ table grapes in- 94612-3550 or call (510) 987-0096. 40 study of water relations in tree ©2005 The Regents of the University of California creased with maturity at harvest; vineyard location and management had a greater im- and vine crops pact than maturity. Johnson et al. Associate Editors Weighing lysimeters are assessing peach Animal, Avian, Aquaculture 109 Reduced-risk fungicides help & Veterinary Sciences and grape water use, to evaluate simpler, Edward R. Atwill manage brown rot and other less expensive methods. Christopher M. Dewees fungal diseases of stone fruit Kathryn Radke 137 Ozone reduces crop yields Barbara A. Reed Adaskaveg et al. Economics & Public Policy New, safer fungicides performed as well as directly and alters crop competition James Chalfant older ones in pre- and postharvest studies, with weeds such as yellow nutsedge Henry J. Vaux, Jr. following wound inoculations and under Food & Nutrition Grantz, Shrestha Amy Block Joy packingline conditions. Smog in some parts of the Central Valley is Sheri Zidenberg-Cherr now worse than Los Angeles; weed competi- Human & Community Development tion in agricultural crops could be altered by Marc Braverman Ellen Rilla increased ozone levels. Alvin Sokolow Land, Air & Water Sciences David Goldhamer Mark E. Grismer Ken Tate Bryan Weare Kearney Research and Extension Center Vital statistics: Natural Resources Adina Merenlender For more information: • 330 acres Kevin O’Hara KREC: http://danrrec.ucdavis.edu/ • Mediterranean climatic zone Terry Salmon kearney/home_page.html • Flat alluvial plain terrain, Pest Management Kearney Agricultural Center: 337 feet above sea level Janet C. Broome www.uckac.edu/uckac • 10.6 inches annual precipitation Kent Daane • Summer maximum mean temp.: 94.9ºF Deborah A. Golino • Winter minimum mean temp.: 39.4ºF Tim Paine • Soil series: Hanford – fine sandy and Plant Sciences sandy loam; Hesperia – fine sandy Kent Bradford loam; Exeter – sandy loam shallow Kevin R. Day • Geographic location: Steven A. Fennimore Latitude – 36º 36’ 1.5” N Carol Lovatt Longitude – 119º 30' 38.8” W Letters

WHAT DO YOU THINK? La Conchita and mudslide science structive flows. Unfortunately, the rapid urbanization of The editorial staff of In the horrific mudslide in La Conchita, the news previously untamed land has often not kept pace with the California Agriculture media were focused on the tragedy and neglected proper mitigation of these hazards, and the occurrences of welcomes your letters, to address the science. The most valuable footage destructive debris flows are increasing (they were there all comments and sugges- tions. Please write to us was taken by a helicopter, which showed the eleva- along, but there were no houses in their path). at [email protected] or tion of the slide area and the fact that it was gently Vegetation does play a role in certain climates. For ex- 1111 Franklin St., 6th sloping, heavily planted land. Apparently it got ample, debris flows are rare on heavily forested slopes, but fl., Oakland, CA 94607. saturated from the rains by holding the water in the become more frequent with deforestation. Fire has been Include your full name soil. There are untold thousands who want to live similarly implicated in increased landslide susceptibil- and address. Letters in the scenic hills; those homeowners need to know ity in areas where it eliminated deep-rooted vegetation. In may be edited for space the science of mudslides. Are the hills trapping all sparsely vegetated desert areas, debris flows are more com- and clarity. the water and does little run off? Why was the root mon and often are the principal mode of erosion and sedi- system of trees not able to cope or was that brush ment transport. In desert settings, the source areas and the and no significant tree cover? Was the original tree depositional fans are relatively easy to map, and hazard cover destroyed in periodic fires, making the hills maps have been prepared for many locations. The problem dangerous? With all these rains, it will be impor- is in translating these maps into concrete public policy. tant to monitor how many slides occur and where. For more information, go to the USGS Landslide Nicholas Terebey, Jr. Web page: http://landslides.usgs.gov/. In addition, see Laveen, AZ the National Research Council report, “Partnerships for Reducing Landslide Risk: Assessment of the National Nicholas Sitar, UC Berkeley professor of civil engineer- Landslide Hazards Mitigation Strategy” (2004): www. ing, responds: nap.edu/openbook/0309091403/html/51.html. The short answer is that there is a lot of research on the subject and we know a lot. Usually the biggest prob- Grandparenting articles still inspire lem is not a lack of scientific knowledge but the fact that I happened to access several public policy does not have a good way of dealing with articles about grandparents geologic uncertainty. In addition, generally there is no raising grandchildren on your money to deal with these problems proactively, unless Web site (March-April 2001). something terrible happens. I found this such interest- Specifically, regarding the possibility of debris flows ing reading, since I raised a (or mudflows), the fact is that they occur in all climatic grandchild in California. She zones. The principal difference is the threshold amount of is now 23. I had a lot of hard precipitation and its intensity. Desert areas of California, roads to cover, but did so with Nevada, Utah and Arizona are well known for their de- a supportive family. I am a Senior Assembly Member on the California Senior Legislature, and as such we prepare yearly proposals to present to the state legislators in hopes they will be picked up

Robert L. Schuster, USGS Schuster, Robert L. and written into law. I would like to work this year on a proposal to present at our session next October relating to desired legislation regarding grandparenting laws. 40 Is there a Web site I can access, or literature that will allow me to familiarize myself with California laws covering this issue, as well as possible problems and concerns I could address in potential legislation at state level? I feel a strong desire to assist at both ends — the young and the old — because I see a need. We all have to deal with abuse, fraud, neglect and caregiving concerns. Sally Wieck, Senior Assembly Member California Senior Legislature Baldwin Park

On Jan. 10, 2005, a landslide struck the community of La Thank you for your continued interest in this important Conchita in Ventura County, destroying or seriously dam- subject. A good Web site to start with is: www.aarp.org/ aging 36 houses and killing 10 people. life/grandparents/helpraising.

52 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 Editorial overview

David A. Grantz Linda Marie Manton Frederick H. Swanson Director, Regional Director, Director, Kearney Agricultural Central Valley, Kearney Research Center Cooperative and Extension Extension Center Collaboration fosters Kearney scientiﬁc achievements

’s Kearney Research and Extension Center (KREC) lies at the heart of one of the most productive and diverse agricultural regions in the world. Also an area of environmental challenges, Kearney’s field sites have supported decades of landmark research, addressing issues as diverse as air pollution effects, the development of exotic specialty crops, and the rapid molecular diagnosis of plant disease. First dedicated as the Kearney Horticultural Field Station in 1965, KREC is one of nine UC Research and Extension Centers (RECs). All are strategi- UCcally located in key agricultural regions of the state, but Kearney is unique among them in its size and scope. Functioning as a small research campus, KREC encompasses 33 specialized laboratories and hosts the UC Kearney Agricultural Center (KAC), with 24 permanent resident faculty. In addition, 20 to 25 faculty from UC campuses and county UC Cooperative Extension (UCCE) offices conduct research at KREC each year. The center currently supports 90 research and extension projects in 130 different field and laboratory locations. KREC also houses the UCCE Central Valley regional office. The cutting-edge and practical research conducted at Kearney has helped San Joaquin Valley agriculture become a $16 billion industry, yielding roughly half of California’s farm production. This issue of California Agriculture commemorates the 40th anniversary of KREC with reviews and reports on recently completed research, much of which has 40 immediate relevance to farmers, packers and shippers. Kearney has seen steady expansion, modernization and diversifica- tion over its 40-year history. Its laboratories and greenhouse facilities rival those found on the UC campuses, and its postharvest facility is state-of-the-art. The center encompasses a variety of alluvial soil types, and more than 50 different crops are cultivated under commercial growing conditions. This combination of land, laboratories and greenhouses enables UC scientists to conduct studies in a carefully managed setting. Professional staff monitor cultivated crops and continually check the operation of sophisticated laboratory facilities. Collaborative environment. Located in the center of a remarkable agricultural region, Kearney fosters interactions with industry, government agencies, environmental and public policy groups, and university scientists. Whether on small research plots, in laboratories or on-site conference facilities, growers and scientists meet here daily in the collaborative spirit envi-

Plum trees: Jack Kelly Clark Kelly Jack Plum trees: sioned by the creators of the land-grant university system.

http://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 53 Jack Kelly Clark Kelly Jack

State-of-the art greenhouses opened in 2004.

Since 1983, the resident research and extension Numerous scientific achievements. Living and faculty have been organized as KAC. About 100 working in the San Joaquin Valley has led to a num- laboratory staff help investigators carry out field ber of important discoveries by KAC faculty and col- and laboratory studies at KREC and off-site in laborators. For example, cultivation techniques are grower fields and packinghouses. now used routinely to manage summer bunch rot in The KAC faculty are multidisciplinary, with grapes; a pruning technique known as the “Kearney scientific expertise in horticultural and agronomic V” allows for dense planting of orchard crops and crops, nematology, entomology, plant pathology earlier harvests (see page 75); and pruning and trel- and physiology, air quality, weed control and mos- lising strategies have been developed to allow raisins quito research. The nucleus of resident KAC scien- to dry on the vine (see page 70). Kearney-based plant tists creates an academic atmosphere that attracts pathologists and plant breeders have addressed the campus and county-based collaborators. The recent problem of root infections that limit yield and plant completion of the U.S. Department of Agriculture’s survival (see page 63). San Joaquin Valley Agricultural Sciences Center Plant breeding efforts at KAC led to the UCBI hy- across the road from KREC has widened the circle brid rootstock of pistachio, combining resistance to of collaboration. Verticillium wilt with tolerance to chilling and salin- The frequent interaction between scientists and ity. A decade after its introduction, the UC-developed industry that is the hallmark of Kearney gener- hybrid is the second most-planted pistachio rootstock ates new questions and research approaches, aids in California. New varieties of many crops have been in the identification of additional research needs, developed at Kearney that address local problems, and extends new information rapidly. Intercampus including cherries that can tolerate San Joaquin Valley collaboration also fuels “outside the box” thinking heat, and the noncaprifying fig ‘Sierra’, which allows and creates efficiencies in the utilization of research more efficient orchard operations and reduces the risk plantings, modern research facilities and special- of fruit diseases. ized equipment. Pest identification and control. Early studies GIS expertise. KAC operates a complex com- at Kearney led to the initial identification of “arm puter network, a graphic arts department and a and cordon death” on grapevines as “Bot canker” Geographic Information Systems (GIS) Facility. GIS (Botryosphaeria rhodina), along with the previously allows researchers to explore the spatial distribu- recognized Eutypa lata. Current research is exploring tion of pests, crops and pathogens, and to study the whether other Botryosphaeria species are responsible interactions that develop as a result of the patch- for this and other disease complexes on grapes in work of land use in the San Joaquin Valley. For California. example, adjacent cotton and alfalfa fields must be New crops and varieties often bring new suites of managed carefully to control Lygus bugs. GIS tech- pests and diseases. In addition, new pests of existing niques now permit KAC-based scientists to post crops are introduced continuously into California. maps that allow growers and pest control advisors Recent research has identified the newest diseases in to enter data on pest populations, pesticide use and grapes, dried plums and peaches. When a new citrus other information directly onto the map-based data peelminer arrived from the south in 1999, threatening archive. Resulting spatial analyses have led to re- a wide range of crops, a technique to raise the pest gional approaches to integrated pest management under laboratory conditions was developed by KAC (IPM) of Lygus bug, leafhoppers, peelminers, avo- scientists. This allowed scientists to investigate con- cado thrips, olive fly and mosquitoes that vector trol techniques. When pistachio nuts became a major human diseases. crop in the San Joaquin Valley, KAC- and campus- GIS techniques facilitate the preparation of based scientists identified major mite and insect pests. special-purpose maps and other materials of KAC researchers developed diagnostic techniques benefit to agricultural clientele, regulators and to predict Botrytis gray mold in kiwifruit, and con- the public. Scientists have access to Web-based ventional and molecular genetic procedures to predict survey techniques hosted by the Kearney GIS Botryosphaeria blight in pistachio and Monilinia Facility. brown rot in tree fruit. Entomologists developed

54 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 Aerial view of the center in May 2004. Jack Kelly Clark Kelly Jack temperature-based emissions from agricul- phenology models to tural operations, a poten- predict outbreaks of tial source of particulate oriental fruit moth, San matter in the air. Other Jose scale and peach research has found that twig borer. These ad- crops in the San Joaquin vance-warning tech- Valley remove substantial niques allow timely ozone air pollution from management and mar- the air, with the unfortu- keting decisions, and nate side effect of reduc- reduce pesticide appli- ing yields and inhibiting cations. A Web-based root development and the IPM decision support uptake of water by certain system (http://tjm. crops (see page 137). uckac.edu) extends Solarization of perennial this information to crops and more recently growers. Kearney sci- of annual crops has been entists have developed developed at Kearney, us- practical manage- ing the heating power of ment techniques for endosepsis and smut in figs, sunlight to reduce soil pathogens (see page 84). This Botryosphaeria blight in pistachio, and aflatoxin work is taking on new importance with the phaseout contamination of pistachios and figs. of methyl bromide. Recently a “double tent” approach Research at Kearney has considerably ad- to solarization developed at Kearney was registered vanced the mating disruption and trapping of by the California Department of Food and Agriculture pest insects. Pheromones (natural insect com- for nursery control of nematodes in containers. KREC munication chemicals) for San Jose scale, vine has supported the IR-4 field research program, which mealybug and peach twig borer were identified evaluates reduced-risk pesticides that would otherwise through collaborations between KAC researchers be unavailable to growers of high-value “minor” crops. and colleagues from around the country. Mating Cultivation techniques developed at Kearney have disruption of oriental fruit moth now controls led to border cutting of alfalfa to keep beneficial in- this pest in stone fruit orchards, the first success sects in alfalfa fields rather than causing their disper- of this kind in North America. sion during complete harvests, and to keep pests such As control technologies were implemented, tar- as Lygus bugs from migrating to cotton. Use of this get organisms have developed resistance. Research technique was reported by 40% of alfalfa growers re- has determined the mechanism of resistance of sponding to a recent KAC survey. Alternaria late blight pathogen of pistachio to Extension to Valley residents. KREC is also home a new class of fungicides, the strobilurins. The to the Central Valley Regional UCCE office, providing existence and spatial distribution of resistance management for county extension efforts throughout of California red scale and San Jose scale to or- the Valley. UCCE provides instruction and demon- ganophosphates and carbamates was discovered stration of improved practices in agriculture, natural at KAC. Using this information, local growers resources, nutrition, family and consumer science, and achieved a 70% reduction in use of these materials, 4-H youth development. Kearney has become a focal and now use insect growth regulators (IGRs) as point of regional activities by UCCE advisors based in pest management tools in the San Joaquin Valley. neighboring counties as well. At KREC, farm advisors Changing pesticide usage leads to other changes work with their academic partners from the campuses in agroecosystems. The adoption of IGRs led to and KAC faculty to conduct agricultural and environ- disruption of the vedalia beetle, which allowed mental research. The meeting facilities at KREC host cottony cushion scale to re-emerge as a serious thousands of visitors each year for CE events designed citrus pest. Again, research at KAC led to the de- to extend applied, research-based information to in- velopment of management techniques for this pest. dustry and other clientele. Field days at KREC provide Such research is critical to production today, and in growers with an opportunity to discover the most adapting solutions for tomorrow’s problems. recent research developments, and to discuss them di- Cultivation techniques. Cultivation research rectly with the scientists conducting the studies. at Kearney has explored the advantages of no-till As the agricultural economy of California enters a planting and cover crops, as well as the use of re- time of increased globalization and competition, and flective and straw mulches to repel insects and the urban development threatens the richest farmland, viruses they carry, suppress weeds, conserve wa- research by Kearney scientists — and its delivery to ter and improve profits (see page 90). This work many clienteles — will continue to provide solutions is now being applied to the mitigation of dust to problems of immediate and long-term concern.

http://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 55 Introduction

1962 Agricultural innovation UC purchases the 195-acre marks 40 years at Kearney Mosesian Ranch

Early crops at the center included walnuts (shown), plums and grapes. May 10, 1965, Reedley Exponent Brother Norbert blesses the Mosesian Ranch at the 1964 groundbreaking; with announces dedication. bowed head is Guy F. “Doc” MacLeod, entomologist and chair of Board of Trust- ees for the M. Theodore Kearney Horticultural Field Station.

hat started 40 years ago as an old ranch at the crops, while at the same time introducing newer heart of the San Joaquin Valley is today a world- specialty crops like blueberries and Asian eggplant. Kearney has also been one of the key testing grounds class research operation, from which flows a for sustainable farming methods, such as integrated steady stream of practical ideas and solutions pest management (IPM), biological control, water 40ready for implementation by the region’s farmers. conservation and nitrogen management. “As growers, we are dealing with new invasive The UC Kearney Research and Extension Center pests, clean air and water regulations, the need to (KREC) has advanced understanding of every as- reduce labor costs, and the search for alternatives to pect of production and environmental management methyl bromide,” says Bill Chandler, who farms in related to the valley’s bounty of fruits, vegetables the Selma area and is active in KREC committees. and field crops. It is no coincidence that Kearney is “We look to Kearney for sound science to help agri- located in what has become the state’s number-one culture grow and thrive.” agricultural county, on land that is some of the most Turn-of-the-century origins productive in the world. With 24 resident faculty conducting basic as well UC has supported off-campus research sites as field research, the center is like a mini-campus, for more than a century. In the 1880s, UC Berkeley with 33 specialized research laboratories and 100 lab- professor Eugene Hilgard established a 20-acre oratory staff members. It also serves more than 100 field station southeast of Tulare for variety tests off-station scientists from three UC campuses and and work on the reclamation of alkali soils. Cooperative Extension offices. Not surprisingly, it is Kearney’s origins go back to the turn of the 20th the most utilized off-campus agricultural research fa- century, when prominent developer M. Theodore Wcility in the UC system. In addition, more than 6,000 Kearney willed his 5,400-acre estate west of Fresno people a year visit the center or participate in its to the University for educational purposes. UC meetings, workshops, field days and seminars. sold the land, generating revenue to establish the Kearney’s 330 acres of research facilities en- Kearney Foundation, which later would supply compass a new state-of-the-art greenhouse, a post- matching funds for a research center named in harvest laboratory, a mosquito control laboratory, Kearney’s honor. multiple insectaries, and academic and administra- In the early 1960s, the San Joaquin Valley was tive offices. Its controlled field studies occupy 260 fertile ground for the expansion of agricultural acres of orchards, vineyards and fields. science and technology. However, prominent San KREC scientists have developed novel cultivation, Joaquin Valley agriculturists knew that problems pruning and planting methods for the major valley peculiar to the valley could “tarnish the bright

56 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 1964 1965 1966 1969 Groundbreaking for two Formal dedication of the Additional 30 acres purchased $165,000 contract houses, an office, a labora- Kearney Horticultural Field awarded to build a tory and machine-storage and Station, May 26 97-by-100-foot building equipment-repair building with 14 offices, laboratories and conference room The research center has brought together the laboratories, fields and collective brainpower needed to solve the most pressing problems of soil, water, fruit growing and pest management.

October 1966 California Agriculture features Kearney. Tea plantings in 1965 were sponsored by Lipton. Sampling sudangrass plots in 1963.

potential of this unique farming area,” according on May 26, 1965, the Kearney Horticultural Field to noted banker and agricultural economist Jesse Station was formally dedicated with several hun- Tapp (Reedley Exponent, June 2, 1965). Challenges dred spectators on hand, according to newspaper 40 included irrigation management, alkali soils, pests accounts. Visitors took tours to see research plant- and diseases, evaluating new tree and vine variet- ings of tea, grapes, peaches, plums, olives, nectar- ies, and developing rootstocks with resistance to ines, almonds, walnuts and other crops that were nematodes and disease. already under way. KREC director Fred Swanson credits Tapp and In the following four decades, the center steadily other midcentury valley agriculturalists for their grew to accommodate new research needs, reﬂect- prophetic understanding that investing in regional ing the region’s rapidly expanding and changing agricultural infrastructure would reap great re- agricultural economy. In 1985, the last 65 acres of wards. “These visionaries knew that the valley was land was purchased, bringing the total acreage to a unique production area and that agricultural re- the present 330. search needed to be local, relevant and accessible,” Meanwhile, the Kearney center expanded its Swanson says. outreach. Educational programs have attracted hun- In 1959 the Fresno County Farm Bureau took dreds of elementary through college-level students the lead in forming the San Joaquin Valley Fruit in recent years, including those attending science and Grape Station Trust, which collected contri- and career fairs, and agricultural tours. butions from farmers, fruit packers, agricultural Kearney scientists advance IPM suppliers and others. Gifts ranging from $2 to $10,000 amounted to $128,500 to match Kearney Kearney research over the decades has Foundation funds. After serious consideration of linked UC faculty to “on the ground” problems. several sites, a committee suggested the Mosesian Interacting closely with growers, UC scientists Ranch, a uniform alluvial plain with favorable developed innovations, including new pest man- sandy loam soil. UC consented and the 195-acre agement technologies. Mosesian Ranch, at the intersection of Manning and The low price and effectiveness of pesticides Riverbend avenues between the cities of Reedley available to farmers after World War II led to their and Parlier, was purchased on Aug. 12, 1962. acceptance as normal and automatic, setting off a Ofﬁcials broke ground nearly 2 years later on ripple of developments. Farmers, farm advisors two houses, a laboratory and a building for ma- and specialists began observing pest resistance and chinery storage and equipment repair. A year later, long-term pesticide residuals on farms and in the

http://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 57 1970 1972 1973 1977 New building Added another Added biological control Capital improvements included five is completed 40 acres unit with quarantine office-laboratory trailers, fruit and laboratory, one of five in vegetable handling lab, volatile the United States storage building, two greenhouses, one potting shed and one storage building

“Pioneering work in integrated pest management for California tree crops was conducted at Kearney.” — Frank Zalom, Cooperative Extension entomologist

Orchard-systems research got under way in the early 1970s. “Grape Day” brings growers to the center in 1974. UC mosquito research was conducted in Fresno throughout the 1970s; the lab moved to Kearney in early 1984.

environment. In other areas, they witnessed the grower who might otherwise be unable to make a phenomena of biological control when, without any profit,” says Charles Summers, a UC Davis ento- pesticide treatment, a pest population would spon- mologist based at Kearney. taneously disappear. Scientific evaluation revealed Other advances include the development of natural pest predators at work. In the 1950s, the rapid molecular assays to detect microscopic fun- campus-based scientists, researchers in the valley, gal spores, as well as their resistance to fungicides. farm advisors and specialists began making con- This could save growers millions of dollars in nections. They studied the concepts of “integrated unneeded fungicide applications, while reducing control” and “economic thresholds” and soon, just environmental damage from pesticide runoff (see as research at Kearney was hitting its stride, “inte- page 115). Also, spurred by the ban of the nemati- grated pest management” was born. cide DBCP in 1979, Kearney research advanced the “Pioneering work in integrated pest manage- understanding of how root growth timing and pat- ment for California tree crops was conducted terns could help identify best nematode treatments at Kearney,” says Frank Zalom, a Cooperative (see page 63). Extension entomologist and former director of the Focus on fruits, nuts and grapes UC Statewide IPM Program. In particular, Zalom credits retired Kearney-based entomologist Richard While working to combat crop pests in environ- Rice and colleagues with the successful develop- mentally sensitive ways, UC scientists have also ment of pheromone trapping, “degree day” models used Kearney as a laboratory to dramatically im- that predict the growth of common stone fruit pests prove the economics of growing perennial crops by such as San Jose scale and peach twig borer, and focusing on varietal improvements and cultivation egg traps for the navel orangeworm, the most im- techniques. From the beginning, deciduous fruits, portant insect pest of almonds. nuts and grapes were the agricultural focus at the Kearney entomologists, plant pathologists and Kearney Horticultural Field Station. nematologists have worked to minimize pesti- Over the years, numerous vineyards were plant- cide use and utilize reduced-risk products for ed at Kearney to conduct experiments on table, pest control. For instance, they advanced the use raisin and wine grapes. Scientists have found, for of plastic reflective mulch to repel aphids that example, that excellent varietal wines can be pro- spread viruses, reducing virus disease incidence duced in the valley’s hot, dry conditions. Numerous up to 80% (see page 90). “This level of disease table grape varieties were studied for optimum reduction assures an acceptable product for the farming practices. Scientists here identified the

58 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 1985 1986 1989 Added parcel across Weighing lysimeters Dedicated new ofﬁce Riverbend Avenue, bring- installed and laboratory building ing total acreage to 330

May 29, 1987, groundbreaking for the new Two huge lysimeters building at Kearney. Left to right: State Sena- have continuously tor Rose Ann Vuich, Lowell Lewis (Associate logged water-use Director of Agricultural Experiment Station), data since 1986. Dick Markarian (California Raisin Bargain- ing Association), Fresno County Supervisor Vernon Conrad, State Assemblyman Bill Jones, Ken Farrell (Vice President, UC Division of Agriculture and Natural Resources), Leo S. Kolligian (UC regent) and mule skinner Bob Simmons on a Fresno scraper, with two show mules. Jack Kelly Clark

The current main office and laboratory building was dedicated in 1989. Left, the dormant tree can be seen through open framework. Right, a frame covered with plastic protects the tree from outside pollen during bloom period. raisin varieties and trellis systems that are most conducive to dried-on-vine (DOV) raisin produc- Legendary “mother” pistachio tree to be retired tion, which could result in substantial savings to Always a curiosity to Kearney visitors is an extra large growers as well as significant improvements in air pistachio tree growing within a huge wooden frame. In quality (see page 70). the spring, the scaffolding in this frame supports a plastic Today, California produces nearly 60% of the cover that allows this “mother tree” to be hand-pollinated. nation‘s peaches, and the region is a significant It was planted as part of a variety block of pistachios producer of plums, dried plums, apricots, al- at KREC by now-retired UC Cooperative Extension po- monds, pistachios and other commodities. UC mologist Carl Optiz. The female parent tree, Pistacia atlan- scientists have increased understanding of stone tica, was crossed in 1980 with a male Pistacia integerrima fruit nutrition, water needs, pest and disease in the same block by Lee Ashworth in the UC Berkeley management, pruning and postharvest handling. Department of Plant Pathology. For instance, they developed high-density prun- The resulting rootstock produces the highest yields of ing systems that have become the industry stan- any pistachio rootstock in California and has an optimal dard (see page 75). combination of tolerance to cold, salinity and Verticillium “The advantage of high-density systems is that wilt. “This means the California pistachio industry can be you get early production. In the third, fourth and extended into areas previously thought too cold for other fifth year, you can get much more fruit per acre rootstocks,” says Cooperative Extension pomologist Louise than an open-vase orchard of the same age,” says Ferguson. “More importantly, trees can be planted in soils Kearney-based pomologist R. Scott Johnson. A not suitable for any other fruit or nut tree in California, ex- successful high-density pruning system has taken cept dates, and irrigated with sub-par water quality. the name “Kearney” worldwide. In addition to This rootstock is now in extensive use in the lower west California, the system is popular in Australia, Chile, side of the Central Valley. Because the Foundation Plant Europe and Canada. Materials Service produces seed of this cross and budwood Grower groups such as the California Tree has been propagated by private source, Kearney’s will be Fruit Agreement (CTFA) provide active support retired later this year and the scaffolding removed. and collaboration. Representing about 1,500 “But, like a good mother,” Ferguson says, “she’ll al- stone fruit growers, three-quarters of whom live ways be there.” — John Stumbos within 60 miles of KREC, CTFA provides substantial funding support for Kearney research into rootstock development, orchard design,

http://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 59 1992 1999 Dedicated F. Gordon Mitchell Renamed the UC Kearney Post Harvest Center Research and Extension Center Jack Kelly Clark Kelly Jack Jack Kelly Clark Kelly Jack

Postharvest research, 1995. F. Gordon Mitchell and LeRoy Giannini, 1992. Kent Daane at 1995 ﬁeld day.

Today, nearly 70% of the Mating disruption research leads to control Clark Kelly Jack California wine and grape of oriental fruit moth in concentrate crush, 95% of stone fruit, in the 1990s. California raisins and 90% of the state’s table grapes are grown in the San

Parlier students attend cen- Joaquin Valley. ter’s ﬁrst science fair, 1990. Winter pruning of orchard trees, February 1997.

water management, IPM and postharvest physi- collecting airborne pollen. Instead, the tree is pains- ology. “It’s really important to have this facility takingly hand-pollinated and the nuts carefully close by,” says Gary Van Sickle, CTFA’s director harvested (see sidebar, page 59). The frame also of research. “Our growers don’t have time for supports netting in the fall to protect the nuts from trial and error, and the center is just a few miles scavenging birds. away. We hold a lot of field days so growers can In another unusual undertaking, Johnson in- see how to best apply the research results.” stalled sixty 6-by-12-foot tanks 4-feet deep on a research plot and filled each one with 19,000 Unique setting fosters innovation pounds of sand. He planted a plum tree, yellow- Swanson says that what makes Kearney unique flesh peach tree and white-flesh nectarine tree in is its mixture of scientists, extension specialists and each tank. The sand supports the trees but sup- research technicians linked to three UC campuses plies no nutrients, permitting scientists to care- and their many different departments. “There’s fully measure and apply all the nutrients for tree a critical mass here of knowledge and experience development. This is the definitive global study that is a catalyst for creative thought and imagina- on peach, plum and nectarine nutrition, Johnson tion,” he says. “At any one time up to 90 different says, and is also the first nutritional study ever research studies are under way on about 50 crops in done on white-fleshed fruit, which now makes up the fields, labs and greenhouses.” 20% to 25% of the California industry. One of the station’s newest additions is a 20,000- As early as 1986, the University constructed square-foot, $2.9 million greenhouse, completed two huge underground scales on the west side of in 2004, which offers 24 individual plant-growing Riverbend Avenue. Called weighing lysimeters, the modules, computer-controlled for temperature and apparatuses — one planted with grapevines, the humidity for year-round research. There are now other with peach trees — have allowed scientists 18 greenhouse projects exploring the biology and to calculate precisely how much water evaporates control of insect and fungal diseases, pest-resistant from the soil and transpires from the tree at any plant selection, the impact of ozone on crop produc- given time (see page 133). “There are very few tion, and specialty crop evaluation. of these in the world large enough for trees and Always a curiosity to Kearney visitors is an vines,” Johnson says. With knowledge about plant extra-large pistachio tree growing within a huge water use gleaned from lysimeter studies, scientists wooden frame. During the bloom period, the frame are better prepared to provide science-based infor- supports a plastic cover that protects the tree from mation to farmers facing any water problem.

60 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 2004 2005 New greenhouse Kearney marks 40 years facility dedicated

In a 2005 report, the Public Policy Institute of

Photos: Richard H. Molinar Richard H. Photos: California predicts that the Valley population will double to more than 7 million by 2045.

UC president (left) Robert Dynes tours Kearney blueberry plots with Manuel Jimenez, April 2004. Jack Kelly Clark Kelly Jack

New specialty crops (clockwise from top left): dragonfruit (exte- rior and interior), lemongrass, jujube, capers, mini watermelons. New greenhouses at night.

field chambers allow UC Riverside plant physi- “Niche” crops keep small farms afloat ologist David Grantz and colleagues to study the Kearney has also taken a leading role in devel- effects of different levels of ozone on plant develop- oping new specialty and “niche” crops that are well ment (see page 137). As early as 1971, William B. suited for the valley’s small-scale growers. Grape Hewitt, who served as director of the San Joaquin tomatoes, a popular item replacing cherry toma- Valley Agricultural Research and Extension Center toes, mini “personal” watermelons, and pitahaya or at Kearney from 1969 to 1974, cautioned that urban dragon fruit are being studied at Kearney in trials growth in the valley must consider the importance by UCCE farm advisor Richard H. Molinar and col- of the area’s agricultural potential. leagues. His plots also feature capers, jujube tree, “Geographically this valley is a basin over which lemon grass, water chestnuts and other plants. air inversion phenomena is common and thus traps Near the eastern boundary of the research sta- air pollutants,” he was quoted in a 1971 Reedley tion, UCCE farm advisor Manuel Jimenez main- Exponent article. “We can not have developments tains 21 varieties of blueberry plants entering their that add to air pollution problems.” eighth year of production (see page 65). Long con- Urban growth continues to be an agricultural sidered unsuitable to San Joaquin soils and climate, concern. The valley has changed dramatically dur- blueberries are now plentiful in Tulare and Fresno ing the past 40 years. In a 2005 report, the Public counties due to studies by Jimenez and colleagues Policy Institute of California predicted that the val- on southern highbush varieties and methods of ley population will double to more than 7 million keeping the plant in its preferred low-pH environ- by 2045. The institute’s experts say that doesn’t por- ment. “We have one variety that’s just exceptional,” tend the demise of valley farming, but it does apply Jimenez says. “The taste is far superior to any I pressure to sell farmland for development prices, have ever tried and the texture is perfect.” grow crops on less space and farm closer to urban populations. Farming at the urban edge “If we, as growers and packers, are to survive The San Joaquin Valley is undergoing tremen- and compete in a global agricultural economy, we dous population growth, which is altering how need Kearney’s continued assistance,” Chandler farmers ply their trade and interact with their ur- says. “With their help, we can become more efficient ban neighbors. In addition, the resulting air pollu- and productive, and continue to produce the safest tion is affecting crop yields and weed interactions. and most affordable food in the world.” On a research plot west of Riverbend, open-top — Jeannette Warnert and Editors

http://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 61 Research update

Jack Kelly Clark Kelly Jack In collaboration with UC Cooperative Extension farm advisors Kevin Day and Harry Andris and pomologist R. Scott Johnson, Crisosto has looked at fertilization, irrigation, bruising thresholds, storage temperature, handling, packing materials, contamination and other factors that can make fruit less attractive or palatable. Their research has resulted in the development of a preconditioning protocol for shippers and a ripening protocol for receivers. The researchers went still further, educating supermarket fruit handlers on how to protect fruit flavor. “The establishment of Taste tests help Kearney researchers to evaluate consumer preferences. this new delivery system is giving excellent results. Fruit are moving faster and a premium has been “Farm to palate” postharvest research paid for preconditioned fruit,” Crisosto says. In kiwifruit, Crisosto has developed ripening ensures high-quality produce protocols and bin storage techniques. He determined optimum maturity time and which packing cientific support for fruit production at the UC materials deliver the fruit to the store with less Kearney Research and Extension Center (KREC) shrivel and pitting. Crisosto and Kearney-based Sdoesn’t stop when the plants are harvested. Con- plant pathologist Themis Michailides developed sumer demand for quality fruit at grocery stores has a curing treatment for kiwifruit to reduce the inci- increased interest in the highly technical scientific dence of the fungal disease botrytis. field of postharvest research, which focuses on fruit Farming practices and postharvest quality. packaging, handling and transportation. Arpaia’s focus is on citrus and avocado. She and “After biting into a mealy or off-flavor peach, her staff continue to collaborate with other citrus consumers won’t likely buy any more,” says researchers to gauge how farming practices influ- Kearney postharvest scientist Carlos Crisosto. “We ence postharvest quality. For example, they are can improve the eating experience by carefully just completing a multiyear project with two UC managing the peach’s journey from the farm to the Riverside entomologists and one plant physiologist consumer’s palate. That expands and strengthens examining the impact of glassy-winged sharpshoot- the market for fresh fruit.” er on the postharvest quality of navel and Valencia At Kearney, the postharvest program acceler- oranges. Arpaia’s group has also collaborated on For more information ated in 1992 when a donation from local stone-fruit projects evaluating the impact of fertilization and KAC Fresh Fruit Postharvest Information: grower LeRoy Giannini allowed for the construc- irrigation practices. Recently, she and her colleagues www.uckac.edu/ tion of a 9,566-square-foot research facility. The conducted taste testing to determine the minimum uckac/research building was named the F. Gordon Mitchell Post maturity level for navel orange harvest. Harvest Center in honor of the namesake’s exten- That work comes on the heels of a successful sive contributions to postharvest science. Mitchell, a multiyear project that determined the ideal time for UC Davis pomologist, retired in 1992. avocado growers to harvest their crop. “We came Two postharvest research scientists are head- up with a way to measure dry weight before ripen- quartered at the Kearney center, UC Davis po- ing and then linked that back to how well people mologist Crisosto and UC Riverside subtropical enjoyed eating the fruit,” Arpaia says. horticulturist Mary Lu Arpaia. In addition, a wide With information from the project, Arpaia has es- variety of off-site UC scientists make use of the tablished minimum maturity standards for the new state-of-the-art facilities, which include 21 walk-in varieties of avocados that have been released by UC. and four reach-in fruit storage chambers, and small- Consumer acceptance. An extensive fresh-fruit scale processing equipment that duplicates the stan- sensory program was developed over the last dard industry machinery. 9 years by Gayle Crisosto, postharvest staff research Protecting fruit flavor. Crisosto focuses on stone associate. She has conducted taste and appearance fruit, kiwifruit and table grapes (see page 103). tests on crops such as peaches, plums, nectarines, With the peach industry, he is addressing the fact table grapes, cherries and kiwifruit. Crisosto has that peach consumption in the United States has re- worked with American consumers and native mained unchanged over the last decade. In surveys, Japanese tourists to test their acceptance of early- consumers misunderstood the difference between harvested Bing cherries at different levels of matu- “mature” and “ripe” peaches, and were turned off rity. The Japanese consumers were satisfied with by lack of flavor, flesh browning and mealiness. lower maturity than the American consumers. “This

62 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 Research update

shows that fruit preferences in Asia are different than fungal disease Septoria spot. After negotiation and those in the United States,” Crisosto says. study, Adaskaveg and his team, working with the cit- Similar work was carried out with 400 American rus industry and the U.S. Department of Agriculture, and 250 native Chinese consumers to determine the arrived at a plan. The team collects and incubates two ethnic groups’ acceptance of ‘Redglobe’ table fruit samples at the center, then assesses them 20 grapes at different maturity levels. days later for Septoria spot. Fruit positive for the dis- At Kearney, Crisosto conducts fruit tasting tests ease are identified and photographed, and the results with panels drawn from staff who have been screened are provided to the packinghouses. This program for their taste acuity and trained for a specific test. was in part responsible for maintaining the $100 mil- “Most of the panelists enjoy it,” she says. “They get lion citrus trade between the two countries. a break from their work and they know they are For other crops, Adaskaveg and his team have making a positive contribution to the furtherance of developed several new reduced-risk postharvest fun- our scientific knowledge of fruit quality.” gicides. They are evaluating new application strategies Managing fungal diseases. UC Riverside plant to improve disease control (see page 109) and have pathologist Jim Adaskaveg is leading postharvest identified diseases like sour rot that have recently be- pathology research on stone fruit, pome fruit, come more of a problem for the stone fruit industry. kiwifruit, pomegranates and citrus. Recently, he Ultimately, all the scientists working on posthar- initiated a citrus incubation program at the post- vest studies at KREC share the same goal, Gayle harvest center that protects the Korean market for Crisosto says. “We want to consistently provide the California citrus industry. In 2003, Korea closed good-tasting fruit to the consumer so they’ll come its market to California oranges after detecting the back for more.” — Jeannette Warnert

Dagger nematode After years of hosting an orchard Stephanie Kaku

Root lesion nematode McKenry V. Michael or vineyard, nematodes will have colonized and reproduced to

Root knot nematode levels that would put a new planting Ring nematode in grave danger.

A variety of plant parasitic nematodes can sap nutri- Vines stunted by root knot nematodes. ents from the roots of trees, vines and field crops. UC nematologists battle tiny underground pests ematodes are the most numerous multicell ani- have traditionally been used to rid soils of nematodes mals on earth. One cup of soil can contain thou- before planting, such as DBCP and methyl bromide. Nsands of the tiny worms. Some are beneficial, but Perennial crops. As part of his focus on peren- many cause significant damage to agricultural crops. nial crops, McKenry has pursued “chemigation” “You can see insects, and diseases often cause as an alternative to preplant methyl bromide soil visible symptoms,” says Philip Roberts, a UC fumigations. McKenry has developed methods Riverside nematologist. “The underground feeding and equipment that use water to carry low-fuming of nematodes can be just as harmful, but it is much biocides (with short half-lives), 5 feet deep. Large more difficult to detect.” volumes of water can also prevent biocides from Roberts and UC Riverside nematologist Mike escaping at the field surface. By 1991, he demon- McKenry, who is based at the UC Kearney Research strated that in highly porous soils, chemigation and Extension Center, preside over a specialized pro- with biocides such as metam sodium could program that offers pest management professionals and vide nematode control equivalent to that of methyl growers the latest information on nematode problems bromide. “Today, new products and equipment for and solutions. Their work is particularly important preplant chemigation are plentiful,” McKenry says. due to past and upcoming bans on chemicals that A promising new natural treatment for nematodes

http://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 63 Research update

was discovered in 1979 by McKenry planting in grave danger. This is called the “replant and his UC Riverside colleagues. problem.” To address the complex issues associated The scientists identiﬁed microor- with replanting, McKenry has made a 70-page re- ganisms that were protecting ﬁve port available for free on his nematode Web site. Fresno County peach orchards from Annual crops. Based at Kearney in the 1980s, root knot nematodes. The fungus, Roberts established two experimental sites to study Dactylella oviparasitica, was found to nematodes in annuals. The research sites were be attacking the pest’s eggs. each inoculated with a distinct species of root knot

Max Clover “This fungus has now been nematode, the most problematic nematode on San Root knot noted in other field settings and in Joaquin Valley commercial farms. nematodes can other regions involving other nematode species,” Over the last 20 years, Roberts and other scientists cause galling and McKenry says. “Research is slow and we still do have identified genes that give plants natural nematode forking of carrot roots. not know how to correctly inoculate fields, but resistance, including in tomato, carrot, cotton, sugar this fungus ranks as a top nematode control agent beet and various dry grain beans. From the work at within nematode-infested soils and is naturally at Kearney, there have been releases of several nematode- work in the San Joaquin Valley.” resistant black-eyed varieties, and breeder release lines Another method of nematode control is the of resistant carrots that are now being used by seed development of resistant rootstocks. In 2003, companies to develop commercial varieties. McKenry’s lab released two new grapevine root- Roberts has also been looking at a range of control stocks that possess broad nematode resistance. options to avoid subjecting nematodes to selection These and other advancements are of particular pressure by repeatedly growing the resistant crops. interest to growers who plan to replant orchards or He has found, for example, that crops susceptible to vineyards. When land that has not previously been nematodes can be planted following some resistant used to cultivate crops is converted to agricultural crops without dramatically reducing yields. Cultural For more information use, nematodes that damage trees and vines are at practices can also play a role, he says. “If you plant Michael McKenry’s nematode site: a minimum. After years of hosting an orchard or carrots at a cooler time of year, when nematodes are www.uckac.edu/nematode vineyard, however, nematodes will have colonized less active, you avoid some plant damage.” and reproduced to levels that would put a new — Jeannette Warnert

Science brief

Lygus study validates treatment thresholds Jack Kelly Clark Kelly Jack

Lygus bugs (Lygus hesperus) are a common insect pest in the San Joaquin Valley, affecting everything from cotton to pistachios and many other commodities. Kearney-based IPM advisor Pete Goodell conducted a study in 1996 of how this pest affects blackeye beans and discovered that the timing of the infestation has more to do with subsequent damage than the sheer number of pests. In brown exclusion cages, varying densities of Lygus bugs (0, 20, 60 and 120) were released before Field assistants Tommy Koga and Jake Gregory sample for and after flowering. The bugs were allowed to feed Lygus bugs in a blackeye bean plot with exclusion cages. for 2 weeks. Yield data was collected and evaluated to determine impacts on quantity and quality. bean plants damaged early were able to compen- Field assistants collected Lygus bugs from the bean sate for any damage caused before bloom.” field with a vacuum sampler. This study, supported by the UC Statewide “We found that the timing of the infestation has IPM Program and Dry Bean Council, showed more impact on yield than numbers,” Goodell says. that treatment thresholds developed for older va- “Beans are more sensitive to pressure from equiva- rieties were still valid for newer varieties. lent Lygus populations after flowering. Presumably, — John Stumbos

64 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 RESEARCH ARTICLE ▼ Blueberry research launches exciting new California specialty crop

Manuel Jimenez Francis Carpenter Richard H. Molinar Kathryn Wright Kevin R. Day ▼

Observational trials at the UC Kearney Research and Extension Center indicate that new southern highbush blueberry cultivars, which require fewer “chill hours” to produce fruit, are well adapted to the San Joaquin Valley climate. In a replicated cultivar evaluation, we quantified yields and identified several productive and flavorful varieties. These initial trials and ongoing studies on irrigation, plant spacing, mulches and pruning Blueberries historically have been grown mostly in the cooler regions of the United States. The recent development of new low-chill cultivars such as ‘Legacy’, above, in concert with will improve the likelihood of innovative growing techniques and strong consumer demand have created an important establishing this promising new specialty crop for the San Joaquin Valley. crop in the semiarid valley. Because ries are one of the most costly crops to hot summers appear to hasten plant de- blueberries are acid-loving, the soil establish. Blueberry establishment and velopment, but could also impact long- must be extensively treated before production costs can exceed $10,000 per term blueberry productivity. planting, at considerable expense. acre, and blueberries require significantly Highbush blueberries (Vaccinium Growers considering planting or more management than most other corymbosum) and low-bush blueberries expanding blueberry acreage should specialty crops (Bervejillo et al. 2002). (Vaccinium angustifolium) are important develop sound business plans, The objective of current UC blueberry commercial types and are native to the accounting for lower future prices research is to develop sound informa- northeastern United States. Rabbiteye tion for selecting cultivars and to verify blueberries (Vaccinium ashei) are also and improved growing, harvesting production practices that will assist produced commercially and are native and packing efficiencies. growers in establishing blueberries. to the southeastern United States. Blueberry is a member of the family The terms “northern highbush” and ue to overproduction, market Ericaceae, which includes woody shrubs “southern highbush” refer to the chill- prices for many crops have been such as azaleas and rhododendrons ing requirement of blueberry cultivars. Ddepressed for several years, resulting that grow well in acidic soils. Highbush Chilling is the accumulated number of in the removal of thousands of acres of blueberries are woody, shallow-rooted hours between 32°F and 45°F that are citrus, stone fruits, grapes and olives perennial shrubs. Although some spe- necessary for a dormant plant to break in the San Joaquin Valley. More than cies grow taller than 20 feet, most cul- vegetative and flower buds. Most north- ever, growers are seeking new crops to tivars are 4 to 10 feet tall at maturity. ern highbush cultivars require more than plant, and many are focusing their at- In established growing regions, plants 1,000 chill hours for bud-break (Gough tention on specialty or alternative crops. reach full production within 6 to 8 years 1991). Chill hours in the San Joaquin Observational trials indicate that new and can remain productive for 20 years Valley range from 600 to 1,200 annually. southern highbush blueberry cultivars or more. Proper pruning, mulching and Previous failures at establishing blueber- are well adapted to San Joaquin Valley pest monitoring are essential to main- ries in California’s warm climate were conditions. These initial trials and other tain plant vigor and productivity. The mostly due to the utilization of northern ongoing studies will improve the likeli- San Joaquin Valley’s warm winters and highbush cultivars, which were poorly hood of establishing this crop in the semiarid valley, a region not tradition- Blueberries are acid-loving plants; therefore, most California ally known for blueberries. However, soils must be acidified for successful plant establishment. prudence is appropriate, since blueber- DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 65 TABLE 1. Estimated North American blueberry acreage, 2003

Region Acres Jack Kelly Clark Midwest Michigan 17,500 Illinois 2,950 Indiana 700 Others 150 Subtotal 21,300 West British Columbia 11,000 Oregon 3,700 Washington 2,000 California 1,300 Subtotal 18,000 South Georgia 6,000 North Carolina 5,000 Mississippi/Louisiana 2,000 Florida 1,200 Growers who are considering planting blueberies or expanding current acreage must develop Texas 1,200 sound business plans to anticipate market changes and production improvements. Morten John- Arkansas 350 son, a Kingsburg dentist and former KREC committee member, attended an open house held for UC Others 250 president Robert C. Dynes, and learned about new blueberry varieties at the center’s research plot. Subtotal 16,000 Northeast adapted to the mild winters of the San making them a potentially lucrative New Jersey 7,500 Joaquin Valley. Breeders in the southeast- specialty crop. Furthermore, reports on Eastern Canada 1,200 ern United States have developed “low- the health benefits of blueberries have New York 1,000 Others 700 chill” southern highbush cultivars by contributed to worldwide consumer in- Subtotal 10,400 crossing northern highbush species with terest (US Highbush Blueberry Council Total North America 65,700 native Florida species. These low-chill 2003). Blueberry acreage in North Source: North American Blueberry Council 2004. cultivars require only 150 to 600 chill America has increased over the last hours for bud-break (Gough 1991). decade and considerably more so during the last 5 years. In 2003, blueberry TABLE 2. Estimated highbush North American production areas blueberry crop, 2004 acreage in North America exceeded Until recently, blueberries were 65,000 acres (North American Blueberry State Fresh Processed Total grown almost entirely in the cooler Council 2004)(table 1). Production and ...... lb. millions ...... regions of the United States includ- disposition figures for 2003 show that Alabama 0.5 0.0 0.5 ing Michigan, New Jersey, Oregon and 69% of the blueberry crop was for fresh Arkansas 1.6 0.0 1.6 Washington, where winter climates and utilization rather than processing, fur- California 3.0 0.0 3.0 the natural acidic soils were uniquely ther illustrating the consumer demand– Florida 2.5 0.0 2.5 Georgia 7.2 7.8 15.0 suited for blueberry production. driven market that blueberries currently Louisiana 0.5 0.0 0.5 However, with the development of enjoy (table 2). Mississippi 1.2 1.4 2.6 improved low-chill cultivars from the The North American harvest usu- North Carolina 16.1 6.4 22.5 Texas 1.0 0.0 1.0 1970s through the 1990s, blueberry pro- ally begins in Florida in early April Others 0.1 0.0 0.1 duction has expanded to the southern and concludes in Michigan and British Total 33.7 15.6 49.3 United States and now, California. Columbia in early October (Agricultural Source: North American Blueberry Council 2004. Increased consumer demand is driv- Marketing Service 2003). The California ing the market for fresh blueberries, harvest typically begins in early May and lasts almost 8 weeks (fig. 1). Furthermore, the arrival of low-chill cultivars has expanded global plantings to Chile, Argentina and tropical Colombia, thereby ensuring fruit availability even during the winter in North America. Planting considerations Blueberries are acid-loving plants; therefore, most California soils must be acidified for successful plant establishment. The optimum soil pH for blueberry culture is 4.0 to 5.2 (Strik et al. 1993). Soil acidification is most often Fig. 1. State blueberry harvest periods that overlap with California’s. achieved using sulfuric acid, which is Source: Agricultural Marketing Service 2003. broadcast over the surface of the soil and DRAFT66 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 TABLE 3. Southern highbush blueberry cultivar characteristics

Cultivar Plant stature Productivity* Harvest period† Fruit size‡ Hand-harvest ease Biloxi Erect High Midseason 70–110 Difficult Bluecrisp Erect Moderate Midseason 65–70 Easy Emerald Erect High Early/midseason 50–80 Moderately easy Jewel Erect High Early 60–100 Moderately easy Jubilee Erect Moderate Early/midseason 80–150 Moderate Legacy Erect High Midseason 55–100 Very easy Millennia Erect Moderate Early/midseason No data Moderately easy Misty Spreading High Early/midseason 80–130 Difficult O’Neal Erect Low Early 100–130 Easy Ozarkblue Erect Moderate Late 50–70 Easy Santa Fe Erect Low Early/midseason 60–70 Easy Sharpblue Spreading Moderate Early/midseason 110–200 Moderate Southern Belle Erect Moderate Early/midseason No data Easy Southmoon Erect Moderate Midseason 60–120 Easy Star Erect Moderate Early 60–70 Very easy Reveille Very erect Low Early 100–130 Moderate * Productivity represents third-year harvest: low < 5 lb., moderate 5-10 lb., high > 10 lb. † Harvest period indicates initiation of harvest: early = initial harvest; early/midseason = 7 days later; midseason = 14 days later; late = 21 days later. ‡ Fruit size represents the number of berries per 6 oz. cup. Although fruit size is genetically predetermined, pruning and other cultural practices can affect fruit size significantly.

then ﬂood irrigated with sufﬁcient water gallon, with sulfuric acid being the least Depending on the buffering capacity of to incorporate it to a depth of 12 inches. expensive and highest in percentage ac- the soil, the acid is converted, neutral- Soil sulfur can be applied but may tive ingredient. All acids are potentially ized and used within several inches require several months to convert to hazardous materials and considerable from where it is applied on the soil. sulfate and change the soil pH. Sulfur care must be taken to minimize worker The soil reaction is summarized as: sul- is not as predictable as sulfuric acid exposure and maintain safe working furic acid plus lime gypsum plus car- for changing soil pH. Therefore, when conditions. bon dioxide plus water. What is unique applying sulfur, additional attention The broadcasting of acids to the soil, about blueberries is that a lower pH is must be given to monitoring soil pH especially sulfuric acid, is performed desirable for optimum plant vigor than and making appropriate adjustments. by companies specializing in the trans- for any other commercial crop. Citric acid and other acidic com- portation of hazardous materials and Blueberry cultivar studies pounds may be used to lower soil pH, custom application of acids, using but they are more costly. specialized application equipment. Trial I. We initiated blueberry ob- Poor water quality also affects blue- Once the acid is applied to the soil, fol- servation trials at the UC Kearney berry plant growth. Many agricultural lowed by an irrigation, the acid reacts Agricultural Research and Extension water sources contain high levels of bi- with calcium carbonate in the soil and Center (KREC) in Parlier in 1997, which carbonates (Gregory 2001; Gaskell 2002). does not present a hazard. The applica- have provided insight to key character- Bicarbonates raise pH and affect the tion of sulfur and other sulfur-based istics of numerous blueberry cultivars. uptake of nutrients by blueberry plants. soil amendments is a common prac- The results of these trials indicated that Additionally, bicarbonate content great- tice in high calcareous western soils. southern highbush blueberry cultivars er than 1.5 to 2.0 milligrams per liter can cause the precipitation of calcium or magnesium carbonate, resulting in a chalky deposit that plugs drip and

microjet irrigation systems (Gregory Jack Kelly Clark 2001). The installation of acid injection equipment may be required to maintain acidic conditions in the irrigation water. Water samples should be tested to determine if treatment is needed. Sulfuric acid (93% to 98% acid) and urea sulfuric acid (27% to 55% acid) are the most common acidifying agents for irrigation water; however, phosphoric acid (52% to 54% acid) and citric acid can also be used (Gregory 2001). Soil sulfur, acetic acid (vinegar) and citric acid are the only acidifiers that are acceptable for organic blueberry production. The ap- Field trials showed that Southern highbush blueberry cultivars are well adapted to the San proximate cost of acid materials ranges Joaquin Valley. These new cultivars, such as ‘Reveille’, above, begin flowering in late winter from approximately $1.00 to $4.00 per and open a harvest window from early May through the Fourth of July. DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 67 Blueberries are acid-loving plants; as a result, most California soils must be treated to well suited for direct sale to consumers. deep was cut on top of the raised beds. lower pH to 4.0 to 5.2, and irrigation water Although ‘Reveille’ does not produce Blueberry plants were planted in is acidified to a pH of 5.0. Left, in a Kearney field trial, overhead misters are close to the large fruit and both cultivars are less the bottom of the furrow, which was plant canopy. Right, overhead sprinklers productive than others, their sweetness then filled with pine mulch. Two drip are being tested to observe plant growth and firmness are distinct and may result lines were placed on the surface of the under a cooler temperature regime. Below, mulch, one on each side of the plant in Kearney field trials, planting beds were in consumer preference and consistent formed using border disking. Blueberry return purchases. row. The emitter spacing was 18 inches plants were then placed in furrows and cov- Trial II. In 2001, a multipurpose rep- apart with each delivering 2 liters of ered with pine mulch. licated trial was established at KREC. water per hour. Irrigation water was Prior to establishing the blueberry trials, acidified to a pH of 5.0 using urea sul- the 2-acre field was fumigated to kill the furic acid fertilizer. The trial received nut grass (Cyperus rotundus) that covered 20 pounds of nitrogen (N) per acre the entire area. In July, a fumigant mix- from a 32% urea ammonium nitrate are well adapted to the San Joaquin ture was applied, 300 pounds of methyl solution (UN32) during the first grow- Valley. We identified several key, early- bromide and 100 pounds of chloropic- ing season, followed by 60 and 90 season cultivars that will likely form rin per acre. A soil test indicated that pounds of nitrogen per acre utilizing the basis for the young industry that is the field pH was approximately 7.0. In urea sulfuric acid (US15: 15% nitrogen, developing in the state (table 3). September, 5 tons of sulfuric acid was 16% sulfur, 49% sulfuric acid)(Gregory Nearly all the cultivars established at broadcast on the surface of the soil us- 2001) in the second and third growing KREC were started from tissue culture ing specialized application equipment. seasons, respectively. and then grown for two seasons by Fall The acid was incorporated to a depth The replicated cultivar evaluation Creek Farm and Nursery in Lowell, Ore. of 10 to 12 inches with flood irrigation, included eight southern highbush cul- Currently, more than 50 cultivars are resulting in a pH ranging from 5.0 to tivars with the exception of ‘Legacy’, under observation at KREC. Although 5.5. A complete fertilizer (15-15-15) which is a northern-southern cross. the data does not provide information was broadcast applied at a rate of 400 Early-season cultivars were ‘O’Neal’, on fruit quality attributes, it is impor- pounds per acre. Rows were set 11 feet ‘Sharpblue’, ‘Misty’ and ‘Star’; midsea- tant to call attention to ‘Southmoon’ and apart. Planting beds were formed using son cultivars were ‘Legacy’, ‘Jubilee’ ‘Reveille’, a couple of cultivars that pro- border discs, then rolled to pack the soil. and ‘Southmoon’; and the lone late- duce outstanding fruit quality and are A furrow 12 inches wide and 6 inches season selection was ‘Ozarkblue’. Each

Fig. 2. Harvest periods for key commercial blueberry cultivars in the San Joaquin Valley. The initiation and termination of harvest will vary as much as 10 days, depending on local weather conditions. DRAFT68 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 trials were also UC Cooperative Extension (UCCE), Tu-

Jack Kelly Clark established, includ- lare County; R.H. Molinar is Small Farms ing an irrigation Advisor, UCCE Fresno County; and K. study, a plant spac- Wright is Research Field Assistant, and ing comparison, a K.R. Day is Tree Fruit Farm Advisor, mulch evaluation UCCE Tulare County. We thank Desmond and a pruning study. Jolly, Director, Small Farms Center, UC Although these tri- Davis, for his leadership in spearhead- als are too young to ing specialty crops research and efforts to report upon at this secure funding; William L. Peacock, Farm time, forthcoming Advisor, UCCE Tulare County, for his results will provide guidance in amending soil pH; Michael critical data that will Yang, Field Assistant, UCCE Fresno UC small farms advisor Manuel Jimenez is leading the effort to develop sound information for selecting blueberry cultivars and assist in the estab- County, and Chu Yang, U.S. Department fine-tuning production techniques. lishment of common of Agriculture Natural Resources Conser- cultural practices vation Service, for their assistance with treatment included seven plants spaced for California blueberries. Several new data collection; the UC Kearney Research 36 inches apart. The experimental de- cultivars have been introduced into the and Extension Center field staff for their sign was a randomized complete block observational collection, and because willingness to make things happen in spite with four replications. of their outstanding characteristics, of often not having the necessary equip- The trial produced a commercial crop some may actually become more im- ment; Dave Brazleton and Dick Mombell, in the second growing season. ‘Misty’ portant than those in current use. We Fall Creek Farm and Nursery, for their and ‘Star’ produced the highest yields are also studying hoop-houses (mobile technical assistance in establishing the among the early cultivars, whereas greenhouses) at KREC, which could research trials and the generous donation ‘Legacy’ was the most productive of the potentially hasten or delay fruit matu- of nearly 3,000 blueberry plants; Jim Greg- midseason-maturing cultivars (table 4). rity so that specific market periods can ory, for his technical support; Verdegaal The harvest period for ‘Star’ in 2003 and be targeted. Moreover, other research- Bros. for their donation and soil application 2004 began the first week of May and ers and growers statewide are con- of sulfuric acid on the research plot and ended after the third harvest 15 days ducting blueberry research. UC farm the irrigation acidification system; Clark later (fig. 2). ‘Misty’ had the longest advisors Mark Gaskell, Ben Faber and Hardy and Mike Taber, Wildlife Control, harvest interval (5 weeks), beginning Ramiro Lobo have established trials for their donation and installation of bird the second week of May and terminat- along the central and southern coast of netting; and Lagomarsino Farms for their ing the second week of June. The har- California, while Abdelaziz Baameur, donation of wood mulch for the studies. vest period for ‘Legacy’ lasted 4 weeks, Calvin Fouche and Mario Moratorio References beginning the third week of May and are conducting blueberry research in Agricultural Marketing Service. 2003. ending during the second week of June. Northern California. Data is not yet Fresh Fruit and Vegetable Shipments. U.S. Most other cultivars required five or available from these trials. Department of Agriculture. www.ams.usda. more harvests, 1 week apart. Yields gen- Since blueberry acreage has in- gov/fv/mncs/shipsumm04.pdf. Bervejillo JE, Jimenez M, Klonsky K. 2002. erally appear to be following the trend creased dramatically to reflect consumer Sample Costs to Produce Fresh Market Blue- of data collected from the observational demand, we assume that prices will de- berries, San Joaquin Valley South, Tulare plots, which are now in their sixth and cline sooner rather than later. Growers County. UC Cooperative Extension. BL-VS-02. seventh year of production. who are considering planting or ex- 16 p. Gaskell, M. 2002. Acid Injection in Ir- panding current acreage must develop Looking forward rigation Water: Improving pH Adjustment sound business plans, which account for for Blueberries. 3 p. www.sbceo.k12.ca.us/ Concomitant with the initiation of lower future prices and improved grow- ~uccesb1/sf1002.htm. Gough RE. 1991. The Highbush Blueberry the cultivar trial in 2001, several other ing, harvesting and packing efficiencies. and Its Management. Binghampton, NY: Staying abreast of technical advances, TABLE 4. Cultivar evaluation yields, 2003 Food Products Pr. p 60–90. and establishing and maintaining good Gregory J. 2001. Uses of Sulfuric Acid as a marketing relationships are essential to Water Amendment in Agriculture. Proceed- Cultivar 2003 2004 ings, International Irrigation Show. The Irri- minimize risks. Additionally, California ...... lb./acre ...... gation Association, San Antonio, TX. Jubilee 6,543ab 7,845ab producers should consider taking lead- North American Blueberry Council. 2004. Legacy 7,279a 9,825a ership roles in blueberry marketing and Blueberry Statistical Record Book, 2004. Misty 4,450c 9,655a promotion activities and organizations, www.nabcblues.org. O’Neal 1,678d 3,564c Strik B, Brunn C, Antonelli A, et al. 1993. Ozarkblue 2,338d 3,281c to sustain blueberry profitability. Highbush Blueberry Production. Pacific North Sharpblue 4,318c 5,921bc West Pub #215. Agricultural Communica- Southmoon 4,695c 5,619bc tions, Oregon State University, Administrative Star 6,034b 9,334a Services A422. Corvallis, OR. 73 p. US Highbush Blueberry Council. 2003. * Treatment means followed by different letters are M. Jimenez is Small Farms Advisor, and significantly different (P < 0.05). Blueberries and Antioxidant Activity. www. F. Carpenter is Research Field Assistant, ushbc.org. DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 69 RESEARCH ARTICLE ▼ The future of California raisins is drying on the vine

William L. Peacock Frederick H. Swanson ▼ Jack Kelly Clark

Scientists at the UC Kearney Research and Extension Center have developed a new method to produce dried-on- vine (DOV) raisins. Prior DOV systems required costly trellising and harvesting equipment, putting DOV out of reach for most growers. Our new, within-row-alternate-bearing DOV (WRAB DOV) method can be used with the existing trellis and no retro- ﬁtting. DOV raisins are machine harvested, reducing human contact and production costs, and improving profitability. Drying raisins on the vine eliminates the need for intensive cultivation to prepare terraces down row middles. This method also removes the problem of using and disposing of paper trays, solving an important air- quality issue for raisin growers.

he California raisin industry consists of about 4,500 growers in the south- Tern San Joaquin Valley, growing raisin grape varieties on 250,000 acres. Over 90% of the raisin crop is produced from the ‘Thompson Seedless’ variety. The 300,000 to 400,000 tons of raisins produced each year constitute about 40% of global production; in 2004, the raisin After more than a century of hand-harvesting and drying grapes on trays to produce raisins, crop had a farm-gate value of one-third California growers now have an economically viable alternative. The alternate bearing, billion dollars. dried-on-vine method (WRAB DOV) developed by Kearney scientists reduces production The traditional method of hand- costs and can be used with existing trellises. harvesting and drying grapes on trays for natural raisins has changed little is labor intensive, requires close super- have smaller wrinkles. This difference over the past hundred years. Most vision and experienced management, is the result of the drying environment. hand-harvested raisin grapes are dried and involves weather risks. In contrast, With tray-drying, the temperature on on individual paper trays placed on a dried-on-vine (DOV) raisins are me- the tray surface can exceed ambient smooth terrace prepared between vine chanically harvested, reducing the labor temperatures by 30°F to 40°F, and rai- rows. When drying is complete, the requirement. The cultivation required to sins dry in 10 to 20 days depending on raisins are rolled up in the paper trays, prepare the terrace is eliminated, along the weather. In contrast, DOV raisins are then the rolls are picked up by hand or with the problem of disposing of paper dried on the vine at temperatures closer mechanically and the raisins are dumped trays (Christensen and Peacock 2000). to ambient and it takes 30 to 40 days to into bulk containers for removal from the DOV raisins have a milder flavor and complete the drying process. field. Paper trays are usually disposed no caramelization compared to tray- The potential for drying raisins on of by burning in the field. This process dried raisins. They are also rounder and the vine was first noted by scientists DRAFT70 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 working at the UC Kearney six blocks (replications) and Research and Extension four treatments, and using five Center (KREC) in 1965. Since vine plots. The three middle then, a number of DOV sys- vines within the five vine plots tems have been developed were used for data collection. by UC researchers and grow- Treatments were WRAB DOV ers. These systems, however, with: (1) no canopy manage- require expensive trellising ment; (2) shoot thinning; and harvesting equipment (3) shoot thinning plus shoot that excludes many growers positioning; and (4) control, tra- from producing DOV raisins ditional tray-drying. Statistical (Christensen 2000). analysis was by ANOVA using We developed a DOV rai- least significant difference for sin method at KREC that has treatment mean separation. opened the door for growers All DOV and tray-drying to produce DOV raisins. The treatments were pruned to five method is based on the sepa- fruiting canes and six renewal ration of fruiting canes and spurs. Fruiting canes were renewal shoots alternating 12 to 15 nodes in length. Canes between vine sections down on the tray-drying treatments the vineyard row. We call the were tied in the traditional method “within-row-alter- Above, dried-on-vine raisins can be mechanically harvested fashion, and canes on DOV nate-bearing dried-on-vine” with a wine grape harvester. Below, hand-harvesting requires were tied using the within-row (WRAB DOV). much higher costs for labor, paper tray disposal and prepara- alternate-bearing system. WRAB DOV is applicable tion of clean middle rows. Shoot thinning DOV treat- to all raisin trellises, and ments occurred in mid-April Production and canopy management raisins are harvested from the vine and consisted of retaining eight shoots using a canopy shaker wine-grape We established a trial plot at KREC on the renewal side of the vine to be- harvester. Prior DOV systems, such as for the dual purposes of comparing come the next year’s fruiting canes. south side, overhead and open gable, WRAB DOV production with tradi- Shoots were selected based on their loca- required expensive trellising and tional tray-drying and evaluating tion. The goal was to establish a clear harvesting equipment. Start-up costs various canopy-management tech- division between the renewal side and were prohibitive for most growers, niques. It was located in a mature fruiting side of the head (trunk). Shoot especially during the recent economic raisin block trellised with a cross-arm positioning occurred in late May, around down cycle. However, the WRAB (18 inches and two wires) and 7-foot berry set, and consisted of wrapping or DOV method can be used with the ex- stakes. The experimental design was twirling five of the shoots that had been isting trellis and no retrofitting. a completely randomized block with retained on the renewal side during the Research began on the shoot-thinning operations (the WRAB DOV method in 1999 next year’s fruiting canes) down at KREC. We compared support wires. WRAB DOV and traditional Yields similar, grades higher

tray-drying, measuring Jack Kelly Clark yield, raisin quality and We found no significant harvest costs over 4 consecu- differences between the yields tive years. Canopy manage- of WRAB DOV and tray-dry- ment, summer pruning and ing for each of 4 consecutive harvesting techniques were years. The average yield dur- developed for WRAB DOV. ing that 4-year period was 2.7 Various trellis widths were tons per acre for the WRAB evaluated to determine the DOV treatment compared impact of trellis expansion with 2.8 tons per acre for the on yield and vine capacity. tray-dried treatment. DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 71 Left, with the traditional method, fruiting canes of ‘Thompson Seedless’ vines are tied in both directions. Right, with WRAB DOV, fruiting canes and renewal sections alternate down the vine row.

DOV raisins graded higher than and facilitated summer pruning. Shoot ing canes out of harm’s way so that the tray-dried raisins when at the same thinning also enhanced the develop- skirt of the canopy could be hedged higher fruit maturity. To compare grades, we ment of the flower cluster primordia prior to summer pruning. This positioning picked tray-dried fruit on Aug. 21, 2003, of retained shoots as reflected in the facilitated winter pruning and tying. and spread it on paper trays. That same increase in cane fruitfulness the fol- Trellis expansion day WRAB DOV vines were summer- lowing year (table 2). pruned to initiate drying on the vine. The cluster begins as a flower cluster Raisins will not dry on trays un- Fruit maturity was measured prior to primordia that forms in the bud during less they are fully exposed to sunlight, harvest by collecting 150 berries from the preceding season. This process be- and this puts serious constraints on each treatment, juicing and then measur- gins in April and continues through the the trellis design and vineyard layout. ing soluble solids in degrees Brix (°Brix) summer. The early season, beginning A wide trellis or narrow row-spacing with a refractometer. Raisin quality was about bloom, is a crucial period that results in shading of the terrace on determined as percentages at “B or bet- determines whether tissue differenti- which fruit is placed on trays to dry. ter” (BorB) grade, “substandard” grade ates into flower clusters or into tendrils. To increase yields, raisin trellises have (sstd.) and mold (mold). Raisin samples Climate, along with the carbohydrate gotten a little larger over the years, were submitted to the U.S. Department nutrition of the bud, plays an important but not much. Research at KREC has of Agriculture’s Agricultural Marketing role. Seasonal variation in vine fruitful- demonstrated that raisin yields will im- Service in Fresno for testing. The raisin ness can usually be attributed to climate prove 15% to 20% with a 7-foot vertical grades were 63% B or better for WRAB conditions in May of the previous year. trellis compared with a 6-foot vertical DOV raisins and 36% B or better for It can also be attributed to cultural trellis (Kasimatis 1976). In addition, a tray-dried, a 43% improvement in grade practices during the previous year that small cross-arm (18 to 24 inches) can (table 1). affected light and temperature within also improve yields and fruit maturity. Shoot thinning of WRAB DOV the canopy and carbohydrate flux in the But, if the trellis size is increased much vines separated the fruiting and re- vine (Williams 2000). more than that and row middles be- newal areas, reduced shoot congestion In our research, shoot thinning in- come shaded, the raisins will not dry. creased fruitfulness in Because of trellis limitations imposed TABLE 1. Quality of WRAB DOV raisins compared years when climatic con- by tray-drying, raisin growers have not with other methods at same fruit maturity, ditions were less than been able to capitalize on new trellis summer pruning and tray harvest (8/21/2003) ideal for flower cluster and canopy management systems. With

Raisin quality differentiation. We be- DOV production, they now can. Fruit lieve that the increased In 2002, we began evaluating the ef- Treatment maturity Mold BorB* Sstd.† cane fruitfulness that re- fect of different trellises (vertical and °Brix ...... % ...... Control: standard tray-dried 18 0.10 36 11 sulted from shoot thin- “T” trellises) on ‘Thompson Seedless’ DOV: ning was the effect of WRAB DOV raisin production. The trial Shoots thinned & positioned 18 0.30 63 5 improved carbohydrate was located at KREC in a 2.5-acre block Shoots thinned only 17 0.20 48 4 nutrition in the retained of mature ‘Thompson Seedless’. The No canopy management 17 0.30 57 4 shoots. vineyard block was originally trellised Mean separation — LSD ‡ ns ns 17 ns .05 Shoot positioning did with 7-foot stakes and 1.5-foot cross- * BorB = B or better. USDA maturity standard for (must grade 35% or above to pass). not affect cane fruitful- arms with two support wires, but was † Sstd = substandard. USDA standard for maturity (grades below 17.1%). ness. However, the shoot retrellised to accommodate this experi- ‡ LSD.05 = least significant difference with a confidence of 95%. positioning placed fruit- ment. The experiment was designed as DRAFT72 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 TABLE 3. WRAB DOV yields increased by expanding width of trellis (summer pruned, 8/13/03; harvested, 9/26/03) TABLE 2. Shoot thinning WRAB DOV increases cane fruitfulness Berry Soluble Raisin weight solids moisture Raisin Raisin Total flower clusters per vine Trellis treatment (8/13/03) (8/13/03) (9/26/03) quality yield* Treatments 2001 2002 2003 g °Brix % % BorB tons/acre Control: standard tray-dried 39 75 42 Vertical & 1 wire 1.9 17.2 14.8 46 1.96 DOV: Vertical & 2 wires 1.8 17.6 14.4 40 2.06 Shoots thinned only 48 73 54 18" cross arm & 2 wires 1.9 17.7 15.0 57 2.54 No canopy management 36 73 37 36" cross arm & 3 wires 2.0 17.5 14.3 49 2.76 48" cross arm & 4 wires 1.9 17.7 14.1 55 3.46 Mean separation — LSD.05* 9 ns 10 Mean separation — LSD † ns ns ns ns 0.44 .05 * LSD.05 = least significant difference with a confidence of 95%. * Raisin yield adjusted to 14% moisture for comparison.

† LSD.05 = least signiﬁcant difference with a conﬁdence of 95%.

a completely randomized block with six similar for all cross-arm widths (table acre vineyard and $125 for a 3-ton-per- blocks (replications) and five treatments 3). A yield increase with no lowering of acre vineyard. and using 40 vine plots. Five vines per fruit maturity indicates that the wider WRAB DOV production costs in- plot were used for data collection. trellises increased the vine’s capacity clude shoot thinning and positioning All trellises utilized 7-foot stakes. for production. to separate the fruiting and renewal Trellis treatments were: (1) vertical, one sections, summer pruning, head fruit Harvesting costs and methods wire on top; (2) vertical, two wires (top removal, machine harvest and trellis and 14 inches below); (3) 1.5-foot cross- WRAB DOV harvest costs were cal- repair. The cost of summer pruning and arm and two wires; (4) 3-foot cross-arm culated for 2- and 3-ton-per-acre vine- head fruit removal varies considerably and three wires; and (5) 4-foot cross-arm yards. This typifies the range in raisin between vineyards. Summer pruning and four wires. yield across the growing region (table costs vary with vineyard age, vigor and Vines for all treatments were 4). Harvest costs for WRAB DOV are vine architecture, and with how well the pruned to five fruiting canes per vine. fixed on a per-acre basis; therefore, in- fruiting and renewal vine sections were Canes were tied using the WRAB creasing yield proportionately decreases separated by shoot thinning. WRAB DOV system. Shoots were thinned the harvest cost per ton. Tray-drying DOV growers do not have the option of and positioned in the spring. Summer costs are fixed on a per-ton basis. For delaying summer pruning beyond late pruning occurred in mid-August. cost comparison, the harvest cost for August if they are to successfully dry Head fruit was harvested and hung tray-drying raisins is about $300 per the raisins on the vine. Vines must be on foliage wires 7 days after summer ton; whereas, the WRAB DOV harvest summer pruned no later than Aug. 20 in pruning. Raisins were hand-harvested cost per ton is $187.50 for a 2-ton-per- order to successfully dry raisins to 16% and weighed, and a subsample moisture or below (USDA mois- was collected for moisture and ture requirement). It takes about TABLE 4. WRAB DOV vine preparation and harvesting costs raisin quality measurements. 6 weeks for raisins to dry to 16%

Raisin yield was adjusted to Vine preparation Vineyard production moisture when vines are summer 14% moisture based on the and harvest cost 2 tons/acre 3 tons/acre pruned in mid-August. The dry- moisture content of raisin $/acre ...... $/ton ...... ing season is essentially over by samples. Shoot selection and mid-October. Raisin yield dramatically positioning (spring) 75.00 37.50 25.00 It is important that green fruit increased with the width of the Summer pruning 100.00 50.00 33.33 (head fruit) be removed prior Harvest green clusters cross-arm, and the results for (hang on wire) 75.00 37.50 25.00 to mechanical harvest, which is 2002 and 2003 were similar. In Mechanical harvest* 125.00 62.50 41.67 a major expense. Head fruit is 2003, the 1.5-foot, 3-foot and Trellis repair after found behind summer-pruned 4-foot cross-arms increased yield machine harvest† 50.00 25.00 16.67 canes, on spurs or on canes that (Winter pruning credit)‡ (50.00) (25.00) (16.67) by 27%, 38% and 73%, respec- Total cost§ 375.00 187.50 125.00 were missed during the summer tively, compared with the verti- * DOV raisins can be hand-harvested for about $75.00 per ton. pruning operation. Head fruit cal trellis. The vertical trellis (no † Trellis damage resulting from mechanical harvesting varies from should be harvested within 1 to cross-arm) was the least produc- little to significant depending on the age and condition of trellis. 10 days of summer pruning and We estimated repair cost at $50/acre. tive. The width of the cross-arm ‡ Winter pruning was $50 per acre less than the cost of placed on trellis wires to dry. If had no significant effect on berry pruning tray-dried vines. head fruit is to dry on the vine weight, soluble solids or raisin § Tray-drying harvest cost averages about $300 per ton. successfully, it must be placed on quality. Raisin moisture was the wire no later than Aug. 20. DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 73 We found no significant differences between yields of dried-on-vine and tray-dried raisins for each of 4 consecutive years.

raisins with a variety of canopy shaker greatly enhance the probability of wine-grape harvesters. Our harvest successful vine drying. cost is based on the use of a contract A ‘Selma Pete’ vineyard on ‘Freedom’ wine-grape harvester. Contract harvest- rootstock is currently being established ing varies depending on location and at KREC. Row spacing and trellis de- acreage. Harvester costs would be much signs that maximize raisin quality and lower for growers who own machines. production will be tested. Mechanizing Raisins are machine harvested summer pruning is an additional objec- much more easily and faster than wine tive. Vines are bilateral, cordon-trained grapes. The dry capstems of the raisins and cane-pruned in order to facilitate are easily detached from the rachis. summer pruning by machine. In ad- DOV raisins harvest predominantly dition to this project, a trial has been as individual raisins rather than as initiated to evaluate the performance clusters. After rainfall, however, the of ‘Selma Pete’ grafted to ‘Thompson capstems rehydrate and mechanical Seedless’ and using WRAB DOV. harvest is more difficult. Typically, the We have completed our fourth year harvesting ground speed is about of research and development of the sys- 3 miles per hour (mph) in the morn- tem, and have extended new informa- ing and 4 mph later in the day. Picking tion to the industry through newsletters, head and fan rotations per minute news releases, seminars and industry Dried-on-the-vine raisins grade higher than (rpm) are increased as the day goes on, meetings. Numerous field days at KREC paper tray-dried raisins. They also have a and both should be evaluated every and in growers’ vineyards have intro- milder flavor, no caramelization, are rounder few hours and adjusted accordingly. duced raisin growers to WRAB DOV. and have smaller wrinkles — the result of a slower drying process that is 30°F to 40°F The fans are adjusted to remove leaves Growers are accepting the system as a cooler than paper trays on the ground. and some substandard raisins. The way of cutting production costs, and picking head, ground speed and fan they recognize the potential for increas- are adjusted so that harvest efficiency ing yield by expanding the trellis. In is maximized while damage to the trel- 2003, about 30,000 tons of DOV raisins Alternatively, growers can harvest head lis is kept at a minimum. Mechanically were produced using this method. fruit and place it on trays to dry or haul harvested raisins can be delivered it to a winery. The amount of head fruit directly to the packinghouse without will depend on the cultivar, the year shaking across a screen to remove sand and vineyard management practices. and other debris, as is often required W.L. Peacock is Farm Advisor, UC Coop- For ‘Thompson Seedless’, five to 10 with tray-dried raisins. erative Extension, Tulare County, and F.H. clusters of head fruit per vine is typical. Trellis damage caused by the ma- Swanson is Director, UC Kearney Research Growers may opt to remove head fruit chine will vary depending on age and and Extension Center, Parlier. The authors as flower clusters in April, which is less construction material. Damage is great- gratefully acknowledge financial support expensive but also reduces yield. est the first year of machine harvesting from the California Raisin Marketing Head fruit that was missed is har- and then diminishes in subsequent Board. vested as green fruit by the mechanical years. We budgeted $50 per acre for trel- harvester along with the raisins, and this lis repair, but we also credited a $50 per References increases the average raisin moisture in acre savings in winter pruning cost. Christensen LP. 2000. Current develop- the bin. Equilibration is complete after ments in harvest mechanization and DOV. DOV research, outreach continues In: Christensen LP (ed.). Raisin Production a few weeks. An average of one green Manual. UC DANR Pub 3393. p 252–63. cluster per vine will raise the average Most of the ongoing DOV research Christensen LP, Peacock WL. 2000. The raisin moisture in the bin by two to three focuses on varietal development. raisin drying process. In: Christensen LP (ed.). Raisin Production Manual. UC DANR Pub percentage points. Growers can opt to ‘Selma Pete’ is a high-producing 3393. p 207–16. hand-harvest WRAB DOV raisins rather cultivar that matures 2 weeks earlier Kasimatis AN. 1976. Increasing growth than use a wine grape harvester. With than ‘Thompson Seedless’; conse- and yield of ‘Thompson Seedless’ vines by hand-harvesting, the worker leaves quently, ‘Selma Pete’ can be summer trellising. Cal Ag 30(5):14–5. Williams LE. 2000. Bud development and the head fruit on the vine so it is much pruned earlier. ‘Selma Pete’ also dries fruitfulness of grapevines. In: Christensen LP less of an issue. At KREC, we have on the vine more quickly than other (ed.). Raisin Production Manual. UC DANR successfully harvested WRAB DOV DOV cultivars. These characteristics Pub 3393. p 24–9. DRAFT74 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 REVIEW ARTICLE ▼ Orchard-system configurations increase efficiency, improve profits in peaches and nectarines

Kevin R. Day Theodore M. DeJong R. Scott Johnson ▼ Photos: Jack Kelly Clark

Simply put, a fruit tree can be viewed as a solar collector that converts sunlight into fruit. The more efficiently this is done, the greater the potential yield and profit. Consequently, growers face an important question when planting an orchard — what planting system to use? While varieties can be changed rather easily through graft- ing, the spacing, rootstock and conformation aspects of an orchard are typically permanent until that orchard is removed entirely, usually only after 15 to 20 years. These aspects can have profound effects on orchard productivity. Research conducted at the UC Tree form and height are two key factors in Kearney Research and Extension Cen- determining how efficiently stone fruit orchards produce fruit and grower profitability. ter on orchard systems — including Kevin Day, UC Cooperative Extension tree fruit higher-density plantings and pruning farm advisor in Tulare County, above, is one of the principal UC scientists involved in studying techniques that enhance light inter- different tree systems. The Quad-V orchard ception — has allowed growers to shown is a popular high-density system. Right, the traditional “open vase” peach tree is less make better-informed decisions when uniform and thus more costly to maintain. planting new orchards.

he productivity of an orchard de- UC Kearney Research and Extension pends in part on how well it collects Center (KREC) for more than 30 years, sunlight.T As such, “light interception” in order to help growers develop proﬁt- is a function of the density, height able and sustainable orchards. and shape of the trees, which in turn Production in orchard systems incorporates the number, angle and production slowly because the trees orientation of their branches. These Since the inception of the fresh- must grow for many years before they characteristics are the primary com- shipping tree fruit industry shortly after reach full size. One of the basic axioms ponents of what is called a “planting the California Gold Rush (during the of planting-system design is that a tree system.” The ideal orchard planting 1860s and 1870s) the state’s dominant should ﬁll its allotted space as quickly system can vary based on numerous orchard system has been the open vase, as possible, and having done so, be factors, including geographic location, with trees trained into a wide “cone” maintained easily within that space. variety and species, soil type, rootstock, tree shape at relatively ample spacings Growers were able to reduce spac- and local cultural and economic con- within the orchard. Originally, trees were ings somewhat in the 1950s due to cerns. However, each system has inher- planted on wide, 22-to-25-foot spacings the introduction of chemical herbi- ent qualities that, if understood, can be (70 to 90 trees per acre) in both directions cides, which reduced and sometimes used to help growers meet their goals to allow for easy access by horses, mules even eliminated the need for cross- for the orchard. UC pomologists have and the primitive mechanized equip- cultivation. Cross-cultivation is culti- been studying and elucidating these ment that was then available. However, vating across the rows of the orchards planting-system characteristics at the such wide-spaced systems came into instead of just down the row; it was DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 75 Photos: Jack Kelly Clark Kelly Jack Photos:

Just because a tree is tall does not ensure that it is inherently more productive or intercepts light more efﬁciently than a shorter tree.

rendered unnecessary when herbicides Kearney was planted in 1972 (Gerdts were introduced that could control et al. 1979). This trial tested four tree weeds between trees, thereby allow- varieties (three peaches and one nectar- ing growers to plant trees closer to- ine, ranging from early- to late-season gether down the row. Tree densities rose in maturity) in three different training slightly to 100 to 120 trees per acre, and systems: the standard open vase (19- efficiencies improved because orchards feet-by-22-feet spacing) versus two reached full production more rapidly. high-density systems (central leader Closer plantings mean that trees do [8-feet-by-15-feet spacing] and paral- not have to grow as large as those that lel-V [10-feet-by-15-feet spacing]). The are wide-spaced. Therefore, they can results of this demonstration block con- reach their ultimate “design size” more firmed that the high-density central- quickly, and consequently also reach leader and parallel-V systems did in- full production more quickly. The trees deed have greater cumulative yields are closer together but also smaller, so than the standard open-vase system that each tree produces less on a per- through the first 7 years of orchard life, The first high-density or “hedgerow” tree basis but per-acre yields are usually when all the trees had matured (table 1). orchard systems were introduced into the the same. Based on these encouraging results, United States from Europe in the 1960s. Top, densities as high as 600 trees per acre In the 1960s, the first high-density another trial orchard was planted in were obtained with trees trained to take up orchard plantings were introduced 1982 (DeJong et al. 1991). This trial less space — a single upright leader (right) to California. These were based on compared open vase to central leader or a parallel-V. Increased yield in the early life of these high-density orchards was European hedgerow systems in which and parallel-V, and also included a confirmed by the first UC orchard-systems row width was reduced to 12 to 15 new type of high-density system called trial planted at Kearney in 1972. feet, and tree distance within each row perpendicular-V. This new system was reduced to 6 to 12 feet, thereby maintained a “standard” (18 feet) row TABLE 1. Cumulative fruit yields (1974–1978) for increasing tree densities from about spacing but used a close (6.5 feet) spac- initial high-density planting trials at Kearney 240 to 605 trees per acre. In addition, ing down the row, thereby achieving Research and Extension Center (peach and nectarine trees planted in 1972) smaller tree shapes were used, usually a tree density of 373 trees per acre. either upright central-leader/spindle Equipment designed for an 18-foot row Variety System* Cumulative yield forms (without the cone), or very TABLE 2. Cumulative fruit yields for four training tons/acre upright palmette or parallel-V forms systems, first 10 years after planting Springcrest Central leader 42.6 (with a much more narrow cone than Parallel-V 44.1 the open vase). It was hoped that these Variety System* Cumulative yield Open vase 23.7 high-density planting systems would in- tons/acre June Lady Central leader 54.6 crease yields — both early in the life of Flavorcrest Central leader 88.4 Parallel-V 46.4 the orchard and at maturity. They were peach Kearney-V† 110.1 Open vase 28.0 also expected to reduce labor costs since Parallel-V 96.1 Fantasia Central leader 76.3 smaller trees mean that many orchard Open vase 107.4 Parallel-V 58.8 Royal Giant Central leader 145.9 Open vase 42.0 operations such as pruning, thinning and harvesting can be performed either nectarine Kearney-V 186.4 O’Henry Central leader 72.3 Parallel-V 148.9 Parallel-V 65.5 mechanically or with mechanically as- Open vase 169.5 Open vase 38.3 sisted devices. * Central leader = 6.5'×18', 372 trees/acre; Kearney-V = * Central leader = 8'×15' spacing, 363 trees/acre; parallel- To test the hypotheses that high- 6.5'×18', 372 trees/acre; parallel-V = 10'×18', 242 trees/ V = 1'×15' spacing, 290 trees/acre; open vase = 22'×19' acre; open vase = 20'×18', 121 trees/acre. spacing, 104 trees/acre. density orchard plantings would in- † Kearney-V was originally called “perpendicular-V.” Source: Gerdts et al. 1979. crease yield and reduce labor costs, Source: DeJong et al. 1991. the first UC orchard-systems trial at DRAFT76 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 Jack Kelly Clark Kelly Jack

A trial orchard planted in 1982 introduced another alternative for high-density stone fruit orchards, the perpendicular V. This system maintained standard 18-feet row spacing but planted trees about 6 feet apart, affording the advantages of early high yields without the additional cost of new equipment for maneuvering in narrow row middles.

generally did not fit easily into a 12- only two scaffolds and these are not al- had four scaffolds instead of two. The to 14-foot row, often forcing growers lowed to branch — are more uniform. Quad-V retained the uniformity as- converting to the close-row systems to Because an orchard can typically pects of the Kearney-V, but allowed purchase new equipment. support only a given amount of fruit for approximately a third fewer trees The results of this trial showed that per acre, systems that use available light per acre — a significant savings. Both like central leader and parallel-V, the and labor most efficiently are gener- systems (with ‘MayGlo’ and ‘Sparkling new perpendicular-V system (later ally most profitable. Just having more May’ nectarines) quickly and efficiently known as the Kearney-V or KAC-V) branches, scaffolds or growing points filled their allotted spaces, had similar significantly improved the early yield does not inherently make trees more pro- light interception (data not shown) and (table 2). Most importantly, perpen- ductive. In the perpendicular-V orchard, therefore similar yields (table 3). The dicular-V allowed growers to adopt a every tree has exactly the same number Quad-V eventually became very popular. high-density system without changing of scaffolds and the variation between During the 1980s and 1990s, fresh- row spacings or buying new equipment. trees is reduced, thereby increasing the market stone-fruit growers were most Another benefit of this trial was the labor efficiencies. Uniformity also al- likely to use high-density systems be- discovery of the importance of tree lows growers to better estimate, plan cause the quick (5 to 9 years) varietal uniformity in orchard management. and develop the crop in an orchard; at turnover meant that fruit harvested early Open-vase orchards have a great deal of the same time, every scaffold projects in the life of the orchard was of relatively variation in tree shapes: the central trunk into the row middle, improving equip- greater value than that harvested toward of each tree typically has three or four ment usage and spray efficiency (Jack the end of the variety’s life. And while primary scaffolds (a major, permanent Dibble, UC Extension Entomologist [re- the developmental costs of high-density “branch” of a tree), and each of these tired], personal communication). plantings were higher than those of stan- then develops into as many as two or Perpendicular-V was the first high- dard plantings, this risk would likely be three secondary scaffolds, which in turn density system that was similar enough offset by the increased profit potential of can branch into perhaps eight to 14 ter- to open vase to be easily understood these high-value commodities. tiary growing points by the time the tree by growers, managers and workers. Profitability of systems explored reaches its ultimate height. In contrast, Perpendicular-V rapidly gained in trees in the perpendicular-V system — popularity in the mid-1980s and soon The aforementioned studies con- where every tree is allowed to develop became known as Kearney-V, or KAC-V. firmed that high-density orchards have The system’s primary the potential to achieve full production TABLE 3. Yields in Kearney-V and Quad-V trial at Kearney Research drawback was tree cost, earlier in their lives than standard open- and Extension Center (nectarine trees planted in 1990) because three to four vase orchards. These studies also showed times more trees were that given equitable light-interception Variety System* 1991 1992 1993 Total initially planted. To ad- characteristics, high-density orchards are ...... tons/acre ...... dress this, a variation no more productive at full maturity than Mayglo Kearney-V 1.06b† 5.36ns‡ 7.25a 13.67ns of the Kearney-V called standard-density plantings. Quad-V 0.37a 5.65 7.53a 13.55 the Quad-V was soon However, these studies did not sat- Sparkling May Kearney-V 0.72ab 5.76 8.87ab 15.35 developed and tested isfactorily answer the growers’ basic Quad-V 0.37a 6.78 10.22b 17.38 at Kearney (Day et al. question of which system is most prof- * Kearney-V = 6'×18', 403 trees/acre; Quad-V = 9'×18', 269 trees/acre. † Mean separation within columns by Duncan’s multiple range test, P ≤ 0.05. 1993). In Quad-V, trees itable. And as the California tree-fruit ‡ ns = not significant. were planted slightly industry became more sophisticated in Source: Day et al. 1993. farther apart (9 to 10 the closing decade of the 20th century, feet) down the row and it was more important to focus on eco- DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 77 TABLE 4. Cumulative yields and economic efficiency of four training systems of ‘Ross’ cling peaches after 5 years in the orchard

System* Yield Crop value Costs Proﬁt tons/acre ...... $ ...... Cordon 58.05c† 12,035 6,477 5,558 KAC-V 67.78b 14,133 5,813 8,320 HiD KAC-V 77.22a 16,149 8,125 8,024 Open vase 51.46c 10,430 4,355 6,075

* Cordon = 8'×13', 419 trees/acre; KAC-V = 6.5'×18', 372 trees/acre; HiD KAC-V = 5.5'×15', 528 trees/acre; open vase = 16'×18', 151 trees/acre. † Mean separation within columns by Duncan’s multiple Fig. 1. Relationship between fruit size and crop load for short range test, P ≤ 0.05. (limited height) and tall (standard height) ‘Summer Bright’ Source: DeJong et al. 1999. nectarine trees pruned to a Quad-V conformation.

nomics rather than on simply trying to open-vase system. Due to the detailed nectarine trees growing as either two- maximize production. record-keeping, this trial also provided leader (scaffold) KAC-Vs or four-leader Cling peaches trial. To explore the tools that growers could use to estimate Quad-Vs (6-feet-by-18-feet and 9-feet- economics of orchard systems, in 1990 relative orchard profitability given par- by-18-feet spacing, respectively). Tree a replicated block of ‘Ross’ processing ticular price, cost and yield scenarios. height was either allowed to develop (cling) peaches was planted at Kearney One surprising result of this study to the common standard of 12 to 13 feet (DeJong et al. 1999). This trial orchard was that although the limited-height or limited to 8 to 9 feet, which meant compared four planting systems with cordon system eliminated the use of that much of the hand labor could be different spacings: KAC-V (6.5 feet by ladders, this system still did not have performed without ladders. In order to 18 feet), high-density (HiD) KAC-V lower per-acre labor costs. One of the get comparable planar bearing area be- (5.5 feet by 15 feet), cordon (8 feet by 13 primary beliefs in fruit production is that tween the two system heights, the limbs feet, and height limited to 7 feet) and ladders add appreciably to the cost of la- of the shorter trees were flattened by ty- open vase (16 feet by 18 feet). The HiD bor since they are heavy and awkward to ing them to an angle of 50 degrees from KAC-V system is even more closely maneuver, and any time spent ascending horizontal, thereby achieving a shorter, planted than the KAC-V, with the goal or descending them is time lost for the flatter tree than is typical for California. of even more rapid full production. primary tasks of pruning, thinning and The results demonstrated that the The cordon system consists of a single harvesting. Since labor accounts for the labor costs for the short trees were an tall trunk, about 3 feet high; scaffolds majority of the orchard costs associated average of 20% to 30% less, depending are bent down off of the trunk in the with fruit production — often $2,000 to on the activity, than those of tall trees. In first and second growing season and $3,000 per acre annually — eliminating addition, the yield potential was similar tied to a temporary support rope that ladders should represent a potentially for short and tall trees (fig. 1), which is suspended down the row at a height significant labor savings. was somewhat surprising and defied of 4 to 5 feet. By tying the scaffolds However, a physiological analysis conventional wisdom. However, due down, earlier fruiting is induced and of the cordon systems in this experi- to the flattened limb orientation, both tree height is reduced, with the goal ment indicated that potential economic systems had similar planar volumes of maintaining a tree height in which efficiencies from lowering tree heights and virtually identical light-interception all labor operations can be performed were not realized because training cor- characteristics, making it not unreason- from the ground without a ladder. The dons to a horizontal position stimulated able to assume that yields should be orchard was 8 acres total, with four excessive vegetative growth (Grossman similar as well. Additional research will replications of each system in 0.5-acre and DeJong 1998). This both increased be necessary to explore the role of these experimental units. All associated costs pruning costs and decreased the trees’ factors in other locations and with dif- and yields were recorded annually for allocation of dry matter into fruit, re- ferent tree varieties. the first 5 years after planting. ducing fruit yields. It became clear that As noted, one of the concerns associ- In this experiment, the two KAC-V if tree heights were to be reduced, it ated with short trees is that of excess systems were the most productive and must be done in a manner that does not vigor. In this study, care was taken to profitable despite having the highest stimulate vegetative growth (vigor) at ensure that the trees were not over- establishment, development and pro- the expense of fruit growth. watered or overfertilized, and there duction costs (table 4). It is important to Nectarine trial. To better understand was no problem with excessive vigor. note, however, that this trial also vividly the relationship between tree height and However, this may not always be pos- demonstrated that the development labor costs, a study with the KAC-V sible under all growing conditions and and initial production costs of these and Quad-V systems was begun at with all cultivars. The ultimate solution high-density systems were 50% to 100% Kearney in 1995 (Day et al. 2003), with to the problem of excess vigor lies in greater than those of the traditional a replicated block of ‘Summer Bright’ developing adequate dwarfing root- DRAFT78 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 Jack Kelly Clark Kelly Jack

in the apple industry (Ferree and Carlson 1987). Next, additional research will be needed to develop sensible and successful training systems that match the growth and production characteristics of trees on these dwarﬁng rootstocks.

K.R. Day is Tree Fruit Farm Advisor, UC Cooperative Extension, Tulare County; and T.M. DeJong is Professor and Cooperative California’s tree fruit industry developed shortly after the Gold Rush of the mid-nine- Extension Specialist, and R.S. Johnson is teenth century. For many years the state’s dominant orchard system was the open vase, Pomology Specialist, Department of Plant with trees trained into a wide “V” shape and ample spacing, allowing for 70 to 90 trees per acre. Above, long-time UC technician Jim Doyle stood next to a standard peach tree Sciences, UC Davis. in the late 1970s. References Day KR, Johnson RS, Crisosto C, et al. 2003. Tree height and volume studies for stocks to fit a range of orchard needs height and form. Just because a tree fresh-shipping stone fruits. California Tree such as variety, season of ripening, soil is tall does not ensure that it is inher- Fruit Agreement Research Reports for 2002. type and pH. ently more productive or intercepts The California Tree Fruit Agreement, Reedley Calif. 5 p. www.eatcaliforniafruit.com/ light more efficiently than a shorter Maintaining competitive orchards growers-shippers/research. tree. Furthermore, fresh-shipping tree Day KR, Johnson RS, DeJong TM. 1993. To remain competitive in an increas- fruits are somewhat unique in that Evaluation of new techniques for improving ingly global market, the California fruit there is frequently an economic reward stone fruit production, fruit quality, and storage performance: High density training tri- industry must develop orchard systems for increased quality rather than just als. California Tree Fruit Agreement Annual that (1) are simple and easily under- an emphasis on total production. The Research Report. 7 p. www.eatcaliforniafruit. stood by managers and workers, (2) are Kearney research efforts have helped com/growers-shippers/research. DeJong T, Day K, Doyle J, Johnson S. 1991. of appropriate cost relative to the poten- shape grower understanding of the rela- Evaluation of training/pruning systems of tial return on investment, (3) minimize tionship between potential yield and the peach, plum and nectarine trees in Califor- reliance on ladders, which increase la- most profitable yield. nia. Acta Hort 322:99–106. bor costs and (4) ensure the production The stone-fruit industry needs the DeJong TM, Tsuji W, Doyle JF, Grossman YL. 1999. Comparative economic efficiency of of high-quality and high-value fruit. development of a proven dwarfing four peach production systems in California. Regimented systems such as the rootstock that can be relied upon to ame- HortScience 34(1):738. KAC-V and the Quad-V are quickly liorate the problem of excessive vigor Ferree DC, Carlson RF. 1987. Apple becoming the norm for many grow- in short trees. Currently, growers still rootstocks. In: Rom RC, Carlson RF (eds.). Rootstocks for Fruit Crops. New York: J ers. These systems can be successfully question whether tree heights can be Wiley. p 107–43. planted without having to alter row- dramatically reduced in a simple, effec- Gerdts M, Andris H, Beutel J. 1979. High spacings or purchase new equipment. tive and sustainable manner. Research at density goes big time. Fruit Grower:9–10. There is also a trend toward some- Kearney is now focusing on developing Grossman YL, DeJong TM. 1998. Training and pruning system effects on vegetative what reduced tree heights as growers such dwarfing rootstocks, which could growth potential, light interception and come to understand the importance potentially revolutionize production in cropping efficiency in peach trees. J Amer of light and its relationship to tree the stone-fruit industry just as they did Soc Hort Sci 123:1058–64. DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 79 RESEARCH ARTICLE ▼

Labor costs may be reduced . . . Research yields size-controlling rootstocks for peach production

Theodore M. DeJong R. Scott Johnson James F. Doyle David Ramming

▼ Photos: Jack Kelly Clark

Production costs in peaches are highly dependent on the cost of labor to prune, thin and harvest trees — costs that would drop if growers had rootstocks that decreased tree size. Collab- orating researchers from UC Davis and the U.S. Department of Agriculture’s (USDA) Horticulture Crops Research Laboratory in Parlier screened several promising clonal, size-controlling rootstocks for California peach production. In field tests, two peach scion cultivars (‘Flavorcrest’ and ‘Loadel’) on five interspecific hybrid rootstocks UC Davis pomologist Ted DeJong and a team of researchers have identified three new rootstocks for peaches to limit tree size and therefore costs for pruning, thinning and yielded positive results. After 8 years harvesting. Clockwise from top left, the industry standard Nemaguard, P30-135, Hiawatha in the orchard, they performed well and K146-43 cultivars. Hiawatha is already available through commercial nurseries while compared with trees on ‘Nemaguard’ the other two have been licensed by UC and USDA. rootstock (the California standard production costs could be substantially clusion of that experiment, we selected for peaches), with reduced trunk cir- decreased if the size of peach trees were 19 size-controlling rootstocks as having cumferences (60% to 95%), reduced reduced enough to eliminate the need commercial potential for California dormant (22% to 80%) and summer for ladders. Such benefits have been peach production. In 1996, a second (40% to 80%) pruning weights, and clearly demonstrated with apples; the trial involving the most promising eight acceptable fruit size and crop yields availability of commercially acceptable (based on ease of propagation and con- size-controlling or “dwarfing” apple sistency of tree characteristics) of those (54% to 98%), since smaller trees rootstocks has revolutionized that in- 19 rootstocks was initiated to test their will be planted at higher densities. dustry (Webster 2001). growth and production characteristics This project has identified three new Until recently, the primary factor under semicommercial field conditions. dwarfing rootstocks with commercial limiting the widespread use of size- Rootstock field trial potential for California peach produc- controlling rootstocks for peach (Prunus tion. One rootstock (‘Hiawatha’) is persica L. Batsch) production was the lack In February 1996, a rootstock field already available through commercial of commercially acceptable rootstocks trial was established at KREC. The nurseries and UC and USDA have compatible with a broad range of scion research block consisted of two peach cultivars (Rom and Carlson 1987). In scion cultivars, ‘Loadel’ (clingstone) and jointly licensed the two others for 1986, a rootstock screening experiment ‘Flavorcrest’ (freestone), June-budded commercial use. for peaches and plums was initiated at onto eight experimental and two control the UC Kearney Research and Extension rootstock genotypes. The rootstocks he annual production costs for Center (KREC). More than 120 Prunus tested were Alace, Hiawatha, Sapalta peaches grown in California are genotypes from a range of genetic (open-pollinated seedlings of Sapa, heavilyT dependent on the costs of hand backgrounds were evaluated for their a Prunus besseyi × P. salicina hybrid), labor for pruning, fruit thinning and ability to root from hardwood cuttings, K-145-5, K-146-43, K-146-44, P-30-135 harvest, which is often done from lad- size-controlling characteristics and com- (P. salicina × P. persica hybrids), K-119-50 ders because of large tree sizes (DeJong patibility with peach (‘O’Henry’) and (P. salicina × P. dulcis hybrid) and two et al. 1999). It is widely recognized that Japanese plum (‘Santa Rosa’). At the con- control rootstocks, Citation (P. salicina DRAFT80 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 TABLE 1. In-row tree spacing and trees/acre for KAC-V and TABLE 2. Trunk circumferences of ‘Flavorcrest’ and ‘Loadel’ scion cultivars at open-vase systems in rootstock trial the end of the seventh growing season (January 2003)

KAC-V Open vase Loadel Flavorcrest Rootstock Tree spacing Trees/ac (ha) Tree spacing Trees/ac (ha) Rootstock Open vase KAC-V Open vase KAC-V feet (meters) feet (meters) ...... cm ...... Nemaguard 6.5 (1.98) 418 (1,035) 16 (4.88) 170 (420) Nemaguard 62 ± 1.0* 44 ± 1.2 70 ± 0.9 50 ± 1.5 P-30-135 6.5 (1.98) 418 (1,035) 16 (4.88) 170 (420) P-30-135 58 ± 0.7 41 ± 1.3 68 ± 1.2 47 ± 1.8 K-119-50 6.0 (1.83) 452 (1,120) 14 (4.27) 194 (480) K-119-50 51 ± 1.0 37 ± 1.1 59 ± 1.4 41 ± 1.0 Alace 6.0 (1.83) 452 (1,120) 14 (4.27) 194 (480) Hiawatha 50 ± 0.8 37 ± 1.0 55 ± 1.1 40 ± 1.4 Hiawatha 6.0 (1.83) 452 (1,120) 14 (4.27) 194 (480) K-146-44 39 ± 0.4 31 ± 0.8 47 ± 1.1 32 ± 0.7 Sapalta 6.0 (1.83) 452 (1,120) 14 (4.27) 194 (480) K-146-43 40 ± 0.2 29 ± 0.8 46 ± 0.7 30 ± 0.7 K-145-5 6.0 (1.83) 452 (1,120) 14 (4.27) 194 (480) * Values represent the mean (SE) of measurements of the four replications in the K-146-44 6.0 (1.83) 452 (1,120) 12 (3.66) 226 (560) high-density KAC-V and standard-density open vase parts of the trial. K-146-43 6.0 (1.83) 452 (1,120) 12 (3.66) 226 (560)

× P. persica) and Nemaguard (P. persica except in years 1, 4 and 7 when they rootstock, fruit were harvested in sev- × P. davidiana, the California standard). were only dormant-pruned (DeJong et eral picks but the data were combined In all, we planted 36 trees of each al. 1999). We adjusted the severity of from all harvests to calculate the mean rootstock/scion combination in two pruning according to the growth char- fruit yield. We also recorded data on different training systems. Four replica- acteristics of each rootstock/scion com- crop load (fruit per tree and fruit size) tions of five trees each were planted bination to optimize crop production but do not report it here. and trained to the two-scaffold KAC-V while developing or maintaining the Rootstock-related differences system (DeJong et al. 1994), and four desired tree shape. The first significant replications of four trees each were fruit set occurred in the third leaf. We Rootstock-related differences in tree planted and trained to the standard also adjusted crop load for tree size by size and vigor were apparent after the multiscaffold open-vase system (Micke hand-thinning to maintain a minimum first year of field growth. As expected, et al. 1980)(see page 75). Between-row spacing between fruit. Because patterns ‘Nemaguard’ was clearly the most vig- spacing was 16 feet (4.88 meters) for all of fruit maturity varied somewhat with orous rootstock, followed in descending rootstock/scion/training-system com- order by K-119-50, P-30-135, Hiawatha, binations, but in-row spacing varied ac- K-145-5, Alace, Sapalta, K-146-43, cording to expectations of the final tree K-146-44 and Citation. However, in the size (table 1). fall of the first year in the field, several We randomized replication of the trees of the Citation, K-145-5, Alace and rootstock/scion combinations within Sapalta rootstocks appeared unhealthy, training-system/scion cultivar subplots. with premature leaf fall and leaf “boat- In-row tree spacing between replica- ing” and “bronzing.” During the subse- tions in the open-vase system was the quent spring several of these trees died shortest tree distance within the rep- while others appeared to recover. But lications plus one-half of the spacing by the following fall, more trees became difference between the replications. For unhealthy and died. As a consequence, example, when a ‘Nemaguard’ replica- these scion/rootstock combinations tion was planted adjacent to a K-146-43 were eliminated from the formal ex- replication, the in-row spacing between periment and we collected no further replicates was 14.0 feet (4.27 meters). data on them. This paper therefore The soil at the site was a well-drained only reports data from the remaining Hanford fine sandy loam. The trees were six rootstocks in the trial (Nemaguard, flood-irrigated to maintain 100% of the K-119-50, P-30-135, Hiawatha, K-146-43 potential evapotranspiration prior to and K-146-44). harvest and about 80% after harvest. Trunk circumference. After 7 years Fertilizer and pesticides were applied in the orchard, overall tree size, as in- according to standard horticultural prac- dicated by trunk circumference, was tices. Weeds were controlled by mowing consistently decreased across all scion/ The objectives of this research were to the row middles and applying herbi- find rootstock-scion combinations with re- training-system combinations by each cides to maintain a 4.9-foot (1.5-meter) duced trunk size, reduced pruning weights size-controlling rootstock (table 2). The weed-free strip down the tree rows. and acceptable fruit size and crop yields. trees on the two most size-controlling Trees were pruned during midsum- Above, the clingstone Loadel scion grafted rootstocks (K-146-43 and K-146-44) had onto rootstock K146-43 was one of the mer and during the dormant season more successful combinations in a trial or- trunk circumferences that were 61% to according to standard recommenda- chard, producing a tree circumference 61% 72% of the trees on ‘Nemaguard’, while tions for the two systems for each year, of current industry standard, Nemaguard. mean trunk circumferences of the oth- DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 81 Fig. 1. Comparisons of pruning weights (summer and dormant Fig. 2. Fruit yields (fresh weight) for ‘Loadel’ and ‘Flavorcrest’ season combined) for ‘Loadel’ and ‘Flavorcrest’ peach trees on peach trees on six different rootstocks in years 3 through 8 in six different rootstocks during the first 7 years in the orchard, the orchard, in (A) open-vase and (B) KAC-V training systems. in (A) open-vase and (B) KAC-V training systems.

ers ranged from 76% of 95% of trees on size-controlling rootstocks over the combinations in each system, other than ‘Nemaguard’. seventh year of pruning compared to note that annual as well as cumula- Pruning weights. Because of the dif- with the more modest differences in tive crop yields per tree on the size- ferences in size and vigor, we pruned trunk circumference, which is also a controlling rootstocks ranged from 54% the trees to maintain the optimum cumulative measurement. For exam- to 98% of ‘Nemaguard’. Crop yields of fruiting potential for each scion/root- ple, the cumulative pruning weights ‘Flavorcrest’ peaches on the K-119-50 stock/training-system combination. for trees on K-146-44 over 7 years and P-30-135 rootstocks tended to be Although there were yearly variations were 17%, 23%, 32% and 26% of trees more similar to those on ‘Nemaguard’ in the amount of brush pruned from on ‘Nemaguard’ for ‘Loadel’/KAC-V, than for ‘Loadel’ peaches with the same each combination, the effectiveness ‘Flavorcrest’/KAC-V, ‘Loadel’/vase rootstocks. Although no fruit-size data is of each rootstock in reducing vegeta- and ‘Flavorcrest’/vase, respectively, presented here, mean fruit sizes among tive growth — compared with trees on while differences in trunk circumfer- the three most vigorous cultivars were ‘Nemaguard’ — was apparent when ences ranged from 61% to 72% of trees very similar, but the three more-size- the annual pruning weights were plot- on ‘Nemaguard’. Similarly, cumula- controlling cultivars tended to have ted for each rootstock/scion/training- tive pruning weights for trees on somewhat smaller mean fruit sizes. At system combination over the 7 years of P-30-135 ranged from 57% to 70% of this time, it is not clear if the fruit size the trial (fig. 1). trees on ‘Nemaguard’, while trunk trends are a real function of the rootstock The effectiveness of the size-controlling circumferences on the same rootstock or the result of the fruit thinners’ ten- rootstocks for reducing the amount of ranged from 92% to 95% of trees on dency to leave more fruit on the smaller dry matter that needed to be removed ‘Nemaguard’. trees relative to the size of the trees. during pruning relative to trees on The relatively high variability in Yields and tree size the vigorous control (‘Nemaguard’) yield from year to year after the first was greater in the larger open-vase The patterns of tree yield during couple of years was due to variability trees than the higher density KAC-V years 3 through 8 in the orchard fol- in pruning and fruit-thinning practices system. Similarly, the effects of the lowed patterns of relative tree size in as well as the biological variability size-controlling rootstocks on reduc- each combination (fig. 2). Trees on the inherent in the combinations tested. tions in pruning weights were greater more-size-controlling rootstocks ap- However, general trends in the data in- with the more vigorous scion cultivar peared to reach full yield potential at dicate that the size-controlling rootstocks (‘Flavorcrest’, an early fresh-market about the same time as trees on the more have the potential to increase the parti- peach) compared with the weaker vigorous rootstocks in the higher density tioning of dry matter to fruit, relative to one (‘Loadel’, an early processing KAC-V system. However, they lagged vegetative growth. If training systems clingstone peach). Perhaps the most behind the vigorous rootstocks in the and tree densities can be adjusted so that interesting aspect of this data was open-vase systems. As a result, it was the total annual accumulation of dry the relatively large reductions in cu- difficult to judge the final relative yield matter in an orchard is comparable to mulative pruning weights with the potentials of the various rootstock/scion what is currently achieved with trees on DRAFT82 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 Jack Kelly Clark

‘Nemaguard’, it should be possible It is widely recognized that production costs could be to maintain or increase crop yields substantially decreased if the size of peach trees were with smaller trees using these size- controlling rootstocks. reduced enough to eliminate the need for ladders. Intensive studies of the growth characteristics of trees on the various will eventually be made available to Micke W, Hewitt AA, Clark JK, et al. 1980. Pruning Fruit and Nut Trees. UC Div of Agric rootstocks indicate that the primary California growers to reduce labor costs Sci Leaflet 21171. differences between the scions on the and improve the production efficiency Rom RC, Carlson RF. 1987. Rootstocks for size-controlling rootstocks and trees on of California peach orchards. Fruit Crops. New York: J Wiley. 494 p. ‘Nemaguard’ are related to shoot inter- Webster AD. 2001. Rootstocks for temperate fruit crops: Current uses, future po- node length and shoot extension growth tential and alternative strategies. Acta Hort rate (Weibel et al. 2002). Furthermore, 557:25–34. these factors appear to be related to T.M. DeJong is Professor and Cooperative Weibel A, Johnson RS, DeJong TM. 2002. differences in diurnal patterns of stem Extension Specialist, and R.S. Johnson is Comparative vegetative growth responses of Pomology Specialist, Department of Plant two peach cultivars grown on size-controlling water-potential (Basile et al. 2003), root vs. standard rootstocks. Amer Soc Hort Sci hydraulic conductance (Basile, Solari, et Sciences, UC Davis; J.F. Doyle was Staff 128:463–71. al. 2003) and the dormant-season starch Research Associate, Kearney Agricultural storage capacity of the various rootstocks Center; and D. Ramming is Research Hor- (Solari and DeJong, unpublished data). ticulturist, USDA Horticultural Crops Research Laboratory, Parlier. Commercial applications References Jack Kelly Clark Three rootstocks from this trial are Basile B, Marsal J, DeJong TM. 2003. Daily currently being recommended for shoot extension growth of peach trees grow- commercial use as size-controlling ing on rootstocks that reduce scion growth rootstocks for California peach and nec- is related to daily dynamics of stem water potential. Tree Physiol 23:695–704. tarine production. ‘Hiawatha’ is a pub- Basile B, Marsal J, Solari LI, et al. 2003. lic domain cultivar and is already being Hydraulic conductance of peach trees grafted commercially propagated. K-146-43 and on rootstocks with differing size-controlling P-30-135 are being licensed jointly by potentials. Hort Sci Biotech 78:768–74. DeJong M, Day KR, Doyle JF, et al. 1994. UC and USDA for commercial use and The KREC Perpendicular “V” (KAC-V) orchard will be marketed as “CONTROLLER 5” system for peaches and nectarines. HortTech and “CONTROLLER 9,” respectively. 4:362–7. DeJong TM, Tsuji W, Doyle HF, et al. These are anticipated to be the first 1999. Comparative economic efficiency of in a series of size-controlling peach four peach production systems in California. rootstocks developed at KREC that HortSci 34(1):73–8. DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 83 REVIEW ARTICLE ▼

Methyl bromide alternatives . . . Soil solarization provides weed control for limited-resource and organic growers in warmer climates

James J. Stapleton

Richard H. Molinar Jack Kelly Clark Kris Lynn-Patterson Stuart K. McFeeters Anil Shrestha ▼

Organic farmers and limited-resource growers in the San Joaquin Valley and other agricultural areas in Cali- fornia — many of whom are ethnic minorities — encounter limited options and environmental constraints when seeking economically viable pest management methods. Over the past 8 years, we have conducted weed research and implementation Soil solarization is a “perfect fit” for small-scale specialty crop growers like Ong Lee Yang projects on soil solarization at the (right), according to Richard Molinar, Fresno County small farms advisor (middle). Central Val- ley strawberry growers can take advantage of hot summers to tarp their fields in July and UC Kearney Research and Extension August between production cycles. Interpreting for the Hmong farmer is Michael Yang (left), Center and on farms in the surround- a UC small farms program representative. ing San Joaquin Valley. In the Kear- ney studies, small-scale solarization must depend on high-value specialty in the San Joaquin Valley and other ag- in parsley reduced weed biomass crops, specialized marketing programs ricultural areas confront limited choices 94% to 99% over the untreated or specific market windows. In many and environmental constraints when control. Furthermore, in an on-farm San Joaquin Valley counties, minori- seeking economically viable pest man- ties, including Asians, Latinos, blacks, agement options. Many specialty crops study, solarization provided effective American Indians and others, operate have few labeled pesticides, due to the weed control for strawberries at a almost 50% of the small farms. Fresno high development and support costs much lower cost than methyl bro- County’s farmers are more diverse than and low returns for the manufacturers. mide, with comparable yields. This those in any other California county, Organic growers are at an additional research has provided guidelines and with a large proportion of Asian and disadvantage due to the restrictions technical support for growers wish- Latino farmers. The Asian farmers are on pesticides allowable under organic ing to implement solarization and primarily Hmong, Lao and other groups certification programs. Also, many related techniques for nonchemical that have emigrated to the United States of the farms are located at the urban- since 1979. Although the total number of agricultural interface, and the use of pes- soil disinfestation in a wide variety small farms in California decreased by ticides and fumigants is further restricted of specialty crops. 9.5% between 1997 and 2002, the num- in fields close to occupied buildings. In ber of minority farm operators increased general, weed management is the most ore than 80% of California farms by 52% (USDA 2004), with the largest pervasive problem for San Joaquin Valley are small family operations, mak- proportional increases in Latinos (65%) specialty crop and organic growers. ingM less than $250,000 in annual gross in- and American Indians (70%). Strawberries have been an impor- come, according to the U.S. Department Although only about 2.5% of all tant specialty crop for San Joaquin of Agriculture’s definition. Of these, 85% California small farms are registered or- Valley small farmers, with the majority gross less than $100,000 annually. Clas- ganic, statewide farmland in production of the acreage located in Fresno and sified as limited-resource farms, these for the organic market totals more than Merced counties. The Fresno County comprise 72% of all California farms. 175,000 acres (CDFA 2002). Limited- Agricultural Commissioner reported To survive economically, small farms resource growers and organic farmers 137 acres of strawberries worth nearly DRAFT84 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 All of the solarization treatments were equally effective in providing weed management, with weed numbers reduced by 86% to 94% and weed biomass reduced by 94% to 99% over the untreated control.

$1.5 million in 2002, albeit less than disease control, the increased solubility developed threshold treatment dos- 1% of the statewide total. The cultiva- of nutrients, and changes in the micro- ages for estimating weed management tion of strawberries in the San Joaquin bial composition of the soil (Stapleton, by soil heating (Stapleton, Prather, et and Sacramento valleys is quite differ- Elmore, et al. 2000). Soil solarization can al. 2000). In a series of experiments, ent from that of the major strawberry be a safe and effective method for con- we subjected the seed of six impor- production areas along the California trolling soil pests, and its effectiveness tant weed species — barnyardgrass coast, with a short, split, fall-spring can be improved by combining it with (Echinochloa crus-galli), London rocket harvest season and most fruit destined other treatments such as fertilizers, cru- (Sisymbrium irio), common purslane for processing and roadside sales, rather ciferous crops and other chemical treat- (Portulaca oleracea), black nightshade than fresh-market shipping. Most San ments including metam sodium. (Solanum nigrum), annual sowthistle Joaquin Valley strawberry farmers are In this report, we describe solarization (Sonchus oleraceus) and tumble pigweed Hmong immigrants who produce much technology for weed management. This (Amaranthus albus) — to timed heat of the crop at the urban-agricultural project, conducted at the UC Kearney treatments at 102, 108, 114, 122, 140 and interface, often on rented land in close Research and Extension Center (KREC) 158°F (39, 42, 46, 50, 60 and 70°C). The proximity to occupied buildings. over the past 8 years, consisted of labora- weed species were selected to represent Historically, most strawberry fields tory development, small-plot experimen- a range of thermal sensitivities and in the San Joaquin Valley are fumigated tation and on-farm validation of data in summer versus winter growing habits. every 2 to 3 years, depending on weed San Joaquin Valley specialty crops. Percentages of viability were deter- pressure and the availability of funds, mined 14 days after removal from the Preliminary laboratory studies while coastal plantings are usually fu- heat treatments. migated every year. However, many of As a first step, earlier laboratory At 158°F (70°C), the seeds of all spe- the strawberry fields in the San Joaquin work done at KREC from 1997 to 1999 cies were dead within 20 minutes, and at Valley are close to shopping centers and residential homes, so growers may find fumigation impractical. Pesticide regulations require that growers maintain buf- fer zones between fumigation areas and occupied dwellings (Carter et al. 2005).

Also, while most fumigations in the Photos: Jack Kelly Clark past were done with methyl bromide/ chloropicrin, the regulatory phase-out of methyl bromide has increased the cost of the remaining supply to the point of being prohibitive. In 2003, many San Joaquin Valley strawberry fields were fumigated with metam sodium, a moderately effective alternative fumigant that is significantly less expensive than methyl bromide (Richard Molinar, UC Farm Advisor, personal communication). An alternative to chemical fumigation is soil solarization, a hydrothermal soil-disinfestation process that utilizes clear plastic mulch to trap solar radiation in moist soil. Solarization during the hot summer months can increase soil temperatures to levels that can kill soilborne disease, nematodes and weeds (Elmore et al. 1993). As with methyl bromide, plants often grow faster and Fig. 1. Estimated lower threshold temperatures and times for iso- produce higher yields when grown in thermal inactivation of seed of six weed species from laboratory solarized soil, as a result of weed and experiments (adapted from Stapleton, Prather, et al. 2000). DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 85 One of the challenges facing many small-scale farmers in California is their close proximity to urban areas. This strawberry field is adjacent to a baseball field at Sunnyside High School in Fresno. Solarization affords a safe, nonchemical alternative for dealing with certain pest problems.

140°F (60°C) all species were dead within for their particular geographic locations. 3 hours. At 122°F (50°C), complete seed To facilitate decision-making, we col- destruction occurred between 4 hours laborated with the Kearney Agricultural (annual sowthistle) and 4.7 days (tumble Center (KAC) Geographic Information pigweed). At 114°F (46°C), thermal death Systems (GIS) unit to create statewide occurred at a range of 15 hours (an- air-temperature maps, using historical nual sowthistle) to 13 days (tumble pig- temperature databases obtained from weed). At 108°F (42°C), barnyardgrass, the National Oceanic and Atmospheric tumble pigweed and common purslane Administration’s National Climatic germinated inside the jars during the Data Center. These maps include both Fig. 2. Air-temperature maps of California in July, showing (A) mean daily maxima (30-year heat treatment. Barnyardgrass, tumble monthly air-temperature maxima (fig. average); and (B) mean number of days in the pigweed and common purslane were 2A), and mean number of days warmer month with maxima greater than or equal to not studied at 102°F (39°C), since 108°F than minimum thresholds (a 95°F [35°C] 95°F (10-year average). Raw data source: Na- tional Climatic Center, NOAA. (42°C) had no effect on their viability (fig. minimum is depicted in fig. 2B), which 1). Additionally, the portion of this labo- can be accessed (www.uckac.edu/iwgss) ratory study conducted at 140°F (60°C) by users who wish to estimate the suit- and 158°F (70°C) was used to assist in ability of their area for solarization. developing guidelines for the weed dis- Within the next few months, soil tem- infestation of container nursery soil us- perature models will be added to the ing a specialized solarization technique Web site, to provide additional decision (Stapleton et al. 2002). support for users (fig. 3). At the present time, however, users should conduct Developing guidelines using GIS tests with soil thermometers or other Solarization is a knowledge-based, temperature-sensing equipment to as- rather than product-based soil disinfes- sess the potential for using solarization tation method. As such, end users are on their own land and for their particu- largely without the benefit and availabil- lar climatic niches. ity of the trained consultants and prod- Small-plot field studies uct support personnel associated with Fig. 3. Typical diurnal soil-temperature curves chemical pesticides. Many growers, pest Several small-plot studies were con- during solarization in the San Joaquin Valley, control advisors and gardeners are often ducted at KREC to support the weed- at three depths. unsure as to the suitability of solarization seed inactivation studies conducted in DRAFT86 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 TABLE 1. Effects of solarization treatments on weed management and marketable yield of parsley foliage

Weed control Parsley yield Treatment* Number Dry wt. Weeding rate Fresh wt. No./0.25 m2 g/0.25 m2 Person-min./2 m row kg/2 m row A 8.0a† 8.7a 0.4a 1.3b B 17.3a 8.6a 0.5a 1.1b C 14.7a 43.1a 0.4a 1.6b D 16.0a 19.6a 0.3a 1.2b E 18.7a 19.1a 0.6a 1.9b F 13.3a 30.6a 0.2a 2.9a G 12.0a 30.9a 0.7a 1.0bc Untreated control 133.3b 721.5b 8.7b 0.1c * A = 1 mil polyethylene on 40-inch bed, buried-drip irrigation; B = 0.6 mil high-density monolayer + UV inhibitor on bed, buried drip; C = 1.4 mil nylon five-layer virtually impermeable film on bed, buried drip; D = 1 mil polyethylene, on multiple bed (three), buried drip; E = 1 mil polyethylene on flat ground, left flat, buried drip; F = 1 mil polyethylene on flat ground, beds formed after Solarization is an effective tool against many shallowly distributed treatment; G = 1 mil polyethylene on bed, surface drip. soilborne nematodes and diseases such as Verticillium wilt, as well † Values followed by different letters are statistically different (LSD test; P < 0.05). as most weeds. The $150 to $300 per acre cost for a row application, above, is much cheaper than methyl bromide fumigation.

the laboratory. In the study described (Calandrinia ciliata), groundsel (Senecio On-farm comparisons near Fresno here from the 2003-2004 growing sea- vulgaris) and annual bluegrass (Poa son, variations of solarization tech- annua) were the most numerous of the To test and compare the herbicidal niques (three plastic formulations; emergent weeds, and redmaids and and strawberry fruit yield effects of so- single bed, multiple bed and flat ground common chickweed (Stellaria media) larization and standard soil fumigants application; surface versus subsurface comprised the bulk of the weed bio- under commercial field conditions, two drip irrigation) were compared in a ran- mass. Results showed that all of the on-farm field experiments were con- domized complete block design to an solarization treatments were equally ducted in the Fresno-Clovis area of the untreated control for weed management effective in providing weed manage- San Joaquin Valley from 1997 to 1999. efficacy and effects on yield of parsley ment (P < 0.05), with weed numbers Field histories and pre-experiment soil (Petroselinum crispum cv. Italian dark- reduced by 86% to 94%, and weed assays confirmed that weeds were the green plain leaf). biomass reduced by 94% to 99%, as only major soilborne pest problem of Beds, where used, were formed and compared with the untreated con- concern. The first experiment (A) was shaped on 40-inch centers in an east- trols (table 1). Similarly, the timed located in the midst of an urbanized west orientation on the Hanford fine hand-weeding showed that all of the area, with residential housing less than sandy loam soil. Three replications of solarization treatments reduced the 100 feet from the edge of the field, and each of the eight treatments were done, labor time necessary to maintain com- was in the third year since the previ- and soil temperatures were continu- mercial weed control in the plots by ous fumigation using methyl bromide. ously monitored in one replication of 92% to 97%. Plot design was a randomized complete each treatment. Each replication was This data clearly demonstrated that block with three replications. Each repli- three beds wide by 30 feet long. Plastic for specialty and organic crops grown in cate consisted of three beds (double-row was laid on July 9, 2003, irrigated via the San Joaquin Valley where chemical planted) on 54-inch centers, 130 feet the surface or subsurface drip systems, herbicides are not available or allow- long. Bed orientation was north-south, and removed on Sept. 4. Following able, solarization can provide excellent and soil type was Greenfield coarse plastic removal, parsley was planted on control of winter weeds. In terms of the sandy loam. Oct. 2. A 6.6-foot (2-meter) row length yield of the parsley foliage, the untreated The preplant soil-disinfestation of each replication was subjected to control was so choked with weed growth treatments included: (1) methyl bro- timed hand-weeding on Jan. 23, 2004. that little parsley could be harvested. In mide/chloropicrin (applied by a com- Additionally, subsamples (2.7 square a commercial situation, the field would mercial applicator on July 30, 1997, feet = 0.25 square-meter quadrats) of have been abandoned with weed growth using an 80/20 mixture at 300 pounds emergent weeds from each plot were this extensive. All of the plots receiving per acre plus plastic tarps left on 2 counted and separated by species on solarization treatments provided an eco- weeks); (2) methyl bromide/chloropic- Feb. 19. To assess the effects of treat- nomic yield of parsley foliage, ranging rin as above plus plastic left on only 5 ments on the yield of parsley foliage, from 6.7-fold to more than 20-fold in- days; (3) solarization with clear plastic two cuttings were made on Feb. 12 and creases over the untreated control. Yields for 4 weeks (July 26 to Aug. 26); (4) March 22. from each of the solarization treatments metam sodium (Vapam, 42% a.i.) at At the time of the initial evaluation were significantly different from the 40 gallons per acre (applied via drip on Jan. 23, 2004, Conyza sp., henbit untreated control, except the one testing irrigation as a bed treatment; applica- (Lamium amplexicaule), swinecress surface drip rather than subsurface drip tion rate expressed as the broadcast (Coronopus didymus), redmaids irrigation (table 1). rate injected through drip lines on Aug. DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 87 Jack Kelly Clark

TABLE 2. Effects of soil solarization and fumigation treatments on weed management and marketable yield of strawberry, Clovis

Strawberry yield Weed control Marketable Treatment* Weeding rate Weed density fresh wt. Person-min./40 row ft. number/m2 kg/40 row ft. Experiment A Metam sodium + solarized 7.6a† nd‡ 42.0 Solarized 8.9a nd 41.7 MBC (+ 14-day solarized) 12.9a nd 40.6 MBC (+ 5-day solarized) 13.4a nd 43.9 Metam sodium 14.1a nd 40.5 Untreated control 26.9b nd 30.9 Experiment B§ kg/30 row ft. In 2002, more than 65 “minor” or specialty veg- Solarized (+ mulch) nd 2.5a 36.5a etable and fruit crops worth more than $75 mil- Metam sodium nd 2.0a 32.8ab lion were grown on 17,000 acres in Fresno County. Solarized (− mulch) nd 1.3a 29.7b Among the producers of those crops is Will Scott, Jr. Metam sodium + solarized nd 1.3a 28.4bc (left) and his brother Melvin (on tractor), who grow Untreated control nd 41.5b 23.5c turnips, peanuts, squash and other crops, and truck * MBC = 80/20 methyl bromide/chloropicrin at 300 lb. per acre; solarized = solarization them to Oakland for sale at a local farmers market. for 4 weeks (July 26–Aug. 26); metam sodium = Vapam (42% a.i. @ 40 gal./acre). Scott is working with Cooperative Extension in ﬁeld † Values followed by different letters are statistically different (LSD test; P < 0.05). trials to demonstrate solarization to fellow mem- ‡ nd = no data collected. bers of the African American Farmers Organization § Solarized = solarization for 4 weeks (Aug. 19–Sept. 18). he helped found.

12) plus solarization for 4 weeks; (5) transplanted through it after solariza- The same weeds that were compara- metam sodium plus plastic left on only tion in one of the treatments. Following tively resistant to chemical fumigation 48 hours; and (6) the untreated control. the soil disinfestation treatments, (cheeseweed [Malva parvifolia], bur- Soil moisture was applied by preirriga- ‘Chandler’ strawberry plants were set clover [Medicago sp.], Spanish clover tion. Strawberry (Fragaria × ananassa out on Sept. 18 at an in-row spacing of [Lotus purshianus], red and white stem cv. Chandler) plants were set out on 12 inches, two rows per bed, and the filaree [Erodium sp.] and birdsfoot tre- Aug. 28 and drip-irrigated. Plant spac- fertilization and insect management foil [Lotus corniculata]) also were more ing down the row was 12 inches, and a practices of the grower were followed. tolerant of solarization. The weeds in standard fertilizer and insect manage- Soil temperatures were monitored in the untreated control were much more ment program was followed according both experiments, and the data collected variable, and included the above weeds to the grower’s preferences. Yields included weed management parameters plus shepherdspurse (Capsella bursa- were taken from 40-foot lengths of the and marketable berry yields. pastoris), cudweed (Gnaphalium sp.), com- middle beds only. mon chickweed, panicled willow herb Weeding costs, person hours The second experiment (B) also was (Epilobium brachycarpum), London rocket, located in a residential area, on Ramona Experiment A. All plots in experiment annual bluegrass, puncturevine (Tribulus sandy loam soil. The site had been A were hand-weeded on four different terrestris), prickly lettuce (Lactuca serriola) fumigated with methyl bromide/chlo- dates (Oct. 6 and Nov. 10, 1997; Jan. 23 and and crabgrass (Digitaria sp.). ropicrin one season earlier. Bed spacing Feb. 17, 1998), based on the weediness of Experiment B. As only a single sea- was 54 inches from center to center, and the untreated control, which was moder- son had passed after the previous soil treatment plots were 30 feet long. Again, ate at the time of each weeding. The time fumigation with methyl bromide, weed the plot was laid out as a randomized taken to hand-weed a 40-foot-long strip of growth was relatively light in experi- complete block, but with four replica- each replication was recorded and totaled. ment B, even in the untreated controls. tions of each treatment. Treatments were All treatments required 48% to 72% (P < For this reason, timed hand-weedings the same as in experiment A, except that 0.01) less time to weed than the untreated were not made, and weediness in the methyl bromide/chloropicrin fumiga- control (table 2). None of the costs for experimental plots was expressed as the tion was not included, and single-bed solarization and/or chemical fumigant number of weeds per 30 feet of bed row. replications were used. Soil in planting treatment were different from each other. As with the previous experiments, all beds was solarized for 4 weeks later in When the hand-weeding labor cost, soil disinfestation treatments provided the year than in experiment A (Aug. estimated at $7.90 per hour, was extrapo- better weed control than the untreated 19 to Sept. 18, 1998) using clear, 1-mil lated to an entire field, use of the soil dis- control, but none of them differed sig- (0.025 mm) polyethylene film. Metam infestation treatments would have saved nificantly from each other (table 2). sodium (Vapam; 42% a.i.) was applied the grower $127 (metam sodium alone) The predominant weeds were in the same way as in experiment A. The to $190 (metam sodium plus solariza- subjected to analysis of variance sepa- film was left on the ground and plants tion) per acre, compared to the control. rately. Results showed that the control DRAFT88 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 of cheeseweed was improved by all sodium application plus solarization more effective and cost more than so- soil disinfestation treatments by about were not different from the untreated larization alone. 50% over the control. All other an- control (table 2). Most of the higher nual weeds, including yellow blossom yields resulted from the first five har- sweetclover (Melilotus officinalis), chick- vests. The yield results are somewhat weed, annual bluegrass, shepherds- different from those of experiment A, J.J. Stapleton is Integrated Pest Manage- purse, crabgrass and spotted spurge and may have resulted from the solar- ment Plant Pathologist, UC Statewide IPM (Euphorbia maculata), were reduced by ization process starting about 4 weeks Program, UC Kearney Agricultural Center nearly 100% by the various treatments. later in the year and resulting in fewer (KAC); R.H. Molinar is Small Farms Ad- None of the treatments provided sat- solarization heat units. In addition, the visor, UC Cooperative Extension, Fresno isfactory control of yellow nutsedge harvest season was terminated at least County; K. Lynn-Patterson is GIS Analyst, (Cyperus esculentus). a week early because of an unseason- and S.K. McFeeters is GIS Assistant, Geo- able hailstorm in June. graphic Information Systems Facility, KAC; Marketable yield of strawberries and A. Shrestha is Integrated Pest Manage- Benefits to users Experiment A. Yield data was taken ment Weed Ecologist, UC Statewide IPM twice weekly for 12 weeks in experi- The results of the KREC field study Program, KAC. We thank Michael Yang, ment A, 3 weeks during the short fall with parsley, along with the two on- Ruth Dahlquist, Carol Adams and Husein season, then 9 weeks in the spring. farm experiments with strawberry, Ajwa for technical assistance with aspects As the harvest data was collected, it showed that solarization is an effica- of these studies; growers Touxia Thaoxachay became apparent that as air tempera- cious weed control option for fall/ and Howard Yang for their cooperation; and tures increased in late May and June, spring specialty and organic crops in Trical for the methyl bromide/chloropicrin production dropped off and the differ- the San Joaquin Valley. Also, there are application. This work was supported, in ences in yield among the different soil economic advantages to using solariza- part, by grants from the UC IPM Research treatments became less marked and tion: the $150 to $300 per acre cost of Grants Program, the UC Center for Pest more variable. Over the entire season, using solarization (row application) is Management Research and Education, and increases in marketable yields from much cheaper than methyl bromide the California Strawberry Commission. the soil treatments ranged from 32% to fumigation. End users should be aware We respectfully dedicate this report to the 42% (P < 0.08), as compared with the that certain weeds, such as yellow and memory of Carol Adams, Principal Statisti- untreated control. As with the weed purple nutsedge (C. rotundus), are not cian, UC Riverside. management data, no differences consistently controlled by solarization. References among the five solarization or fumi- The advantages of solarization Carter CA, Chalfant JA, Goodhue RE, gation treatments were found. Apart include ease of use by the grower, McKee GJ. 2005. Costs of 2001 methyl bro- from weed growth, the only appar- relatively low treatment costs, and mide rules estimated for California straw- ent pest problem during strawberry no hazards to the grower, workers or berry industry. Cal Ag 59:41–6. [CDFA] California Department of Food production was root damage caused public, which is important at the urban- and Agriculture. 2002. State organic crop by the feeding of Hoplia callipyge beetle agricultural interface. Solarization is ac- and acreage report. California Organic In- grubs, which occurred in the untreated ceptable for use in organic production, spection Services. www.cdfa.ca.gov/is/fveqc/ organic.htm. control plots only. Care was taken and no permits or pesticide reporting Elmore CL, Roncaroni JA, Giraud DD. 1993. during harvest to select strips from is required. As an option, the film can Perennial weeds respond to control by soil untreated control plots that were not be kept in place after treatment as a bed solarization. Cal Ag 47(1):19–22. affected by the insect-feeding damage. mulch to improve the cost/benefit ratio. Stapleton JJ. 2000. Soil solarization in Experiment B. various agricultural production systems. Crop Berries were harvested On the other hand, disadvantages Protect 19:837–41. twice weekly for 11 harvests in experi- include the unavailability of land for Stapleton JJ, Elmore CL, DeVay JE. 2000. ment B. Total yield per plot was taken 3 to 4 weeks during the summer, and Solarization and biofumigation help disinfest soil. Cal Ag 54(6):42–5. and culls separated out for marketable maintenance of the plastic (patching Stapleton JJ, Prather TS, Dahlquist RM. yields. As opposed to experiment A, holes when necessary). Solarization 2000. Implementation and validation of a significant differences in yield (P < 0.05) must be timed soon after the spring thermal death database to predict efficacy were observed among some of the treat- harvest is completed but before plant- of soil solarization for weed management in California. UC Plant Protect Quarterly ments (table 2). Soil disinfestation treating for the next crop. Furthermore, 10(3):9–10. www.uckac.edu/ppq. ments increased berry yields 21% to 55% little expert consultation is available Stapleton JJ, Prather TS, Mallek SB, et over the untreated control. Solarization (as opposed to chemical pesticide rep- al. 2002. High temperature solarization for with the plastic film left in place as a resentatives). Combining solarization production of weed-free container soils and potting mixes. HortTech 12:697–700. mulch during plant growth resulted in with chemical fumigants such as me- [USDA] US Department of Agriculture. 2004. the highest marketable berry yield. tam sodium is another attractive option 2002 Census of Agriculture. National Agricultur- However, yields following metam for commercial users, but may be no al Statistics Service. www.nass.usda.gov/census. DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 89 RESEARCH ARTICLE ▼ Mulches reduce aphid-borne viruses and whiteflies in cantaloupe

West Side of the San Joaquin Valley or in combination and can only be Charles G. Summers (John LeBoeuf, Pest Control Advisor, distinguished from each other serologi- Jeffrey P. Mitchell California Melon Research Advisory cally. We did not attempt to distinguish James J. Stapleton Board, personal communication). While between the viruses in this study. ▼ susceptible to a number of diseases and Recently, the silverleaf whitefly insect pests, by far the most important (Bemisia argentifolii Bellows and Perring) problem over the past several years has emerged as a serious late-season We compared reflective plastic and has been the complex of aphid-borne pest, resulting in a 13% decrease in wheat straw mulches with conven- viruses, primarily cucumber mosaic cantaloupe acreage in Fresno County tional bare soil for managing aphid- virus (CMV), watermelon mosaic virus (Jetter et al. 2001). Whiteflies damage (WMV) and zucchini yellow mosaic vi- cantaloupe by sucking the juices out of borne virus diseases and silverleaf rus (ZYMV), which vary in severity by the plants, which can kill young plants whitefly in cantaloupe. The occur- season (Hartz et al. 1996). Disease sever- and severely stunt older ones, resulting rence of aphid-borne virus diseases ity increases as the growing season pro- in almost no fruit set. While silverleaf was significantly reduced with both gresses, and fall is the worst time of the whitefly transmits a number of viruses mulches as opposed to bare soil, and year for all of the viruses. The viruses (Gemini viruses) in other parts of the reflective plastic performed better kill and stunt plants, reducing yield. United States, no whitefly-borne viruses than wheat straw. Silverleaf whitefly These diseases are transmitted by have been found so far in California. several aphid species (Kennedy et al. Currently, there are no cantaloupe numbers, both adults and nymphs, 1962) that are commonly found in the varieties resistant to the aphid-borne were reduced equally by plastic San Joaquin Valley, and they are char- viruses (CMRAB 2003). In addition, mulch and wheat straw, and were acterized by leaf symptoms including insecticides offer little relief because significantly lower than with bare severe distortion (crinkled, puckered the viruses are acquired by the aphids soil. Reflective plastic produced ma- and misshapen), yellowing, and light- and transmitted to the plants within ture melons sooner and more cartons and dark-green mottling (mosaic symp- seconds, long before the aphid vector per acre than the other production toms). These viruses may occur singly acquires a lethal dose of insecticide systems. The reflective plastic system also produced a greater number of large-size melons, which are favored

in the late-season market. Plants Jack Kelly Clark grown over straw mulch produced higher overall yields, including large- size melons, than those grown over bare soil.

phid-borne viruses and silverleaf whitefly can completely devastate Acantaloupe crops, causing serious economic losses to growers. The California Melon Research Advisory Board (2003) lists the management and control of aphid-borne viruses and whitefly as a top pest-management research priority. At the UC Kearney Research and Exten- sion Center (KREC), we studied the use of reflective plastic mulch and straw mulch to manage aphid-borne viruses and silverleaf whitefly in cantaloupes Kearney-based entomologist Charlie Summers, left, has been studying the use of mulches to without the use of pesticides. limit damage to melons from silverleaf whitefly and virus-carrying aphids. Reflective plastic Late-season cantaloupes are grown mulch with a lattice network cut down the center, right, can be applied following machine- on approximately 5,000 acres on the planting. The plants emerge through the holes in the lattice network. DRAFT90 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 When grown over reflective plastic mulch, cantaloupes can produce both acceptable yields and sizes even under heavy pressure from aphid-borne viruses and silverleaf whitefly, without multiple insecticide applications.

(Gibson and Rice 1989). Insecticides openings down the center and can be may actually enhance the spread of applied following machine planting; the aphid-borne viruses by stimulating vec- plants then emerge through the open- tor activity (Ferro et al. 1980). Many in- ings. (Reflective plastic mulch is slightly secticides stimulate the aphid’s nervous more expensive than black plastic system, causing it to move from plant mulch, but the latter does not work to to plant very rapidly. This results in the repel aphids or whiteflies.) infection of more plants than would oc- As part of a conservation tillage study, cur in those visited by a nonintoxicated we also found that wheat straw mulch aphid, which settles down and feeds on can help manage aphid-borne viruses one plant before moving to another one. and whitefly in cucurbits. In zucchini This occurs before the insecticide has a squash grown over straw mulch, yields lethal impact on the aphid. In contrast, were as high and the incidence of aphid- whitefly infestations can be somewhat borne virus diseases was no greater than relieved by imidacloprid, a systemic in plants grown over reflective plastic insecticide. However, the development mulch (Summers et al. 2004b). Plants of resistance to imidacloprid and other grown over straw mulch produced higher insecticides among whiteflies is a major yields than those grown over plots that concern (Prabhaker et al. 1998; Elbert had received a preplant application of and Nauen 2000; CMRAB 2003). imidacloprid. Straw mulch also deterred colonization by silverleaf whitefly and Mulches reduce crop viruses reduced the incidence of squash silver- Reflective, metalized plastic mulch, leaf (Summers et al. 2004b). formed by adhering a thin coat of alu- Field study, sampling protocols minum ions to a sheet of polyethylene, has been shown to help control other In studies at KREC, we compared types of aphid-borne viruses as well as the effectiveness of reflective plastic and whiteflies. This control is due to the fact wheat straw mulches for the manage- that reflective plastic mulch reflects ul- ment of aphid-borne viruses and sil- traviolet (UV) wavelengths, unlike black verleaf whitefly in cantaloupe. We also or clear plastic mulches. Flying aphids compared both strategies to conven- and whiteflies are repelled by these UV tional bare soil production. wavelengths. The outcome is to delay The study field was prepared for and reduce the incidence of aphid-borne planting using conventional procedures: viruses. Stapleton and Summers (2002) disking, preirrigation, fertilizer applica- showed that the onset of virus disease tion (500 pounds per acre of 15-15-15 symptoms was delayed by 3 to 6 weeks [nitrogen-phosphorus-potassium]), in plants grown over this mulch, which herbicide application (soil incorporated was critical for normal flowering and bensulide [Prefar] at 6.5 quarts per acre) fruiting. In addition, reflective plastic and bed shaping (60-inch beds). The mulch delayed and reduced the severity reflective plastic mulch was applied us- of silverleaf whitefly infestations in zuc- ing standard mulch-laying equipment. chini squash, pumpkins and cucumber Surface drip-tape was laid down the (Summers and Stapleton 2002). This center of each bed under the plastic. mulch was as effective as a preplant ap- Drip tape was also placed down the plication of imidacloprid in managing center of all remaining beds. The wheat Reflective mulch, top, is made from a thin coat of aluminum adhering to a sheet of whiteflies. straw was spread by hand. To accom- polyethylene. Unlike black or clear plastic Reflective plastic mulch can be ap- modate seeding, holes were cut every mulches, UV light is reflected back into the plied with ordinary mulch-laying 30 inches into the plastic mulch and the sky and canopy, repelling insects and boost- equipment or by hand, and holes are straw was “scratched” aside every 30 ing plant growth. Wheat straw mulch, middle, also reduced virus diseases and whitefly then cut into the mulch to accommodate inches down the center of the beds. infestations over plants grown on bare soil hand-planting. In addition, a version Each treatment consisted of three with no mulch, bottom. of this mulch has a lattice network of beds with two unplanted beds between DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 91 Photos: Jack Kelly Clark

Left, a complex of different mosaic viruses can cripple crop production by slip (when the melon separates from mulch confers a growth advantage to stunting plant growth and reducing the stem with a very slight pressure). plants. yield or killing cantaloupe plants out- Harvesting occurred over a 10- to 14- right. Middle, silverleaf whitefly has Aphid numbers and virus incidence emerged as a serious late-season pest, day period. Melons were sorted by size, contributing to a 13% decline in Fresno and the number in each size category In 2002 and 2003, the cotton/melon County cantaloupe acreage. Right, the was determined. Then weights in each aphid (Aphis gossypii) was the only cotton/melon aphid is a highly efficient vector of three mosaic viruses (cucum- size category were taken. The number aphid species present. This aphid is ber, watermelon and zucchini yellow). of cartons per acre for each size category a highly efficient vector of all three was then calculated. viruses. In 2002, there appear to have Statistical analysis. All data presented been two aphid flights (a large number in the text and figures were analyzed by of winged aphids flying for a period analysis of variance. Means followed by of time) after seedling emergence, treatments. Plots were 220 feet long and the same letter(s) are not significantly in mid-August and mid-September. replicated five times in a randomized different at P = 0.05, using Fisher’s pro- During mid-August 2002, the number complete block design. Three seeds were tected LSD. of winged aphids per leaf was signifi- planted per hill, and following seedling cantly higher on plants grown over bare Plant growth compared emergence, the stand was thinned to one soil than on those grown over plastic or plant per hill for an average of 88 plants During the first 2 weeks of the 2003 straw mulch (fig. 2A). The higher aphid per bed. ‘Top Mark’ melons were planted study, plant growth was identical across counts in plants grown over bare soil re- on July 21, 2002, and ‘Ovation’ were all three production systems (reflective sulted in a significantly higher incidence planted on July 31, 2003. plastic mulch, wheat straw mulch and of virus disease in late August and Biomass. Biomass was sampled in bare soil)(fig. 1). However, at 2 weeks early September (fig. 2B). At the same 2003 as a measure of plant growth. the plants grown over the reflective time, significantly lower aphid counts Beginning 1 week after seedling emer- plastic mulch began a rapid growth in plants grown over straw and plastic gence, one plant from a guard row of spurt; at 3 weeks, they had accumulated mulch resulted in lower virus incidence. each plot (one of two rows on either twice as much dry matter as plants The reflective plastic mulch maintained side of the data-collection row) was grown on bare soil, and more than three virus incidence below 10% through selected at random, cut at the soil sur- times as much by 4 weeks. mid-September. face and placed in a paper bag. It was The large increase in weight per In 2003, a major aphid flight occurred then returned to the laboratory, dried at plant observed on Sept. 21 reflects the in early August and populations of 160°F and weighed. earlier development of fruit in plants Insects and disease. Following grown over plastic. Similarly, plants seedling emergence, 10 plants in the grown over straw mulch also accu- middle of each center row were marked mulated dry matter more rapidly than with surveyor’s flags. Beginning ap- those grown over bare soil. However, proximately 2 weeks after seedling this dry matter increase was not as rap- emergence, the newest fully expanded id as that in plants grown over reflective leaf on each marked plant was carefully plastic. In earlier studies, we found that turned over and the winged aphids and compared to straw mulch and bare soil, adult silverleaf whiteflies were counted. reflective plastic reflects a significantly At approximately 4 weeks after emer- higher rate of photosynthetically ac- gence, a 3-week-old leaf from each tive radiation (PAR) back into the plant marked plant was removed, placed in a canopy (Summers et al. 2004a). This re- locking plastic bag and returned to the flected PAR is intercepted and absorbed laboratory. A 1-square-inch plug was by the canopy, resulting in increased removed from each leaf and the number photosynthesis, which in turn results in of silverleaf whitefly nymphs present increased plant growth. While not as ef- was counted. The 10 marked plants ficient as reflective plastic, straw mulch were visually examined weekly for vi- still reflects twice as much PAR back rus disease symptoms. into the canopy as bare soil (Summers et Fig. 1. Biomass accumulation in cantaloupe Yields. Melons from the center row al. 2004a). We believe that this reflected plants grown under three production of each plot were harvested at full PAR from the plastic and the straw systems, 2003. DRAFT92 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 Fig. 2. Populations of (A) winged aphids and (B) virus disease Fig. 3. Populations of (A) winged aphids and (B) virus disease incidence and in cantaloupe plants grown under three incidence in cantaloupe plants grown under three production production systems, 2002. systems, 2003.

winged aphids were very high a week The number of whitefly nymphs per and the bare ground plots, although after seedling emergence. Maximum square inch of leaf surface closely paral- adult densities were just the reverse. aphid numbers again occurred in plants leled the adult counts, with populations Adult densities were higher in 2003 be- grown over bare soil (fig. 3A). The in- in plants grown over reflective plastic cause the temperatures in August and cidence of virus-infected plants closely and straw mulch significantly (P < 0.05) September were considerably warmer, followed that of winged aphids per leaf, below those in bare soil. This trend per- with daily maximums 3°F to 5°F higher with the highest percentage of infected sisted throughout the season (fig. 4B). than in 2002 (National Weather Service plants grown over bare soil (fig. 3B). The overall density of nymphs in 2003 2004). This resulted in an additional Disease incidence in plants grown over was double that in 2002 for both mulches one-half generation of whitefly (eggs bare soil increased rapidly beginning in were laid and immature insects devel- early September and peaked near 100% oped but did not reach the adult stage) by early October. The infection rate in 2003. Unlike squash and pumpkin, in plants grown over straw mulch re- cantaloupe does not show symptoms of mained under 50%, while those grown squash silverleaf. over reflective plastic reached only 15%. Earlier, greater yields with mulch Whitefly populations Melon plants grown over reflec- In both 2002 and 2003, adult white- tive plastic mulch produced ripe fruit fly numbers were significantly higher 7 to 10 days earlier than those grown in plants grown over bare soil (fig. 4). over either straw mulch or bare soil. Whitefly numbers per leaf in 2002 were In 2002, yields (cartons per acre) were approximately twice those observed significantly lower in all size categories in 2003 with both mulches and bare in all three production systems. There ground. Whitefly numbers were sig- were no large-size melons (#12) in any nificantly (P < 0.05) fewer, however, in production system in 2002. Among the plants grown over both reflective plastic remaining sizes, production was signifi- and straw mulch in both years. While cantly (P < 0.05) higher in plants grown whitefly densities increased as the over plastic mulch, followed by those season progressed, numbers in plants grown over straw mulch. Both produc- grown over reflective plastic and straw tion systems resulted in significantly mulch remained low (fig. 4A). Even in higher yields than the conventional bare mid-September, the number of adults soil system (fig. 5). Fig. 4. Populations of silverleaf whitefly per leaf in plants grown over these (SLWF) (A) adults and (B) nymphs in canta- While yields were significantly mulches was less than those in bare soil loupe plants grown under three production higher in all sizes in 2003, the same gen- in mid-August (fig. 4A). systems, 2002. eral trend was observed in 2002. Total DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 93 Jack Kelly Clark

Fig. 5. Cantaloupe yields in cartons per acre, 2002 and 2003.

production was highest in plants grown Reductions in both the incidence over plastic and second highest in straw. of virus diseases and the severity of UC technicians Albert Newton (left) and Yields from plants grown over straw whitefly infestation in plants grown Matt Milton conduct an aphid count at an were only equal to those from the bare over these mulches contributed to the early cantaloupe trial using plastic reflective soil control in the largest and smallest higher yields. Plants grown over these mulch (silver) and spray mulch (white). sizes (#12 and #23). In all other size mulches also produced more large-sized categories, yields from the straw mulch fruit, which are at a premium late in maize dwarf mosaic virus in sweet corn. J plots were significantly (P < 0.05) higher the season. In our studies, these higher Econ Entomol 73:730–4. than bare soil. cantaloupe yields and larger sizes were Gibson RM, Rice AD. 1989. Modifying accomplished without the use of insec- aphid behaviour. In: Minks AK, Harrewijn P Fewer insecticide sprays needed (eds.). Aphids: Their Biology, Natural Enemies ticides. We are currently working with and Control. Amsterdam: Elsevier. p 209–24. When grown over reflective plastic growers to increase the adoption of Hartz TK, Mayberry KS, Valencia J. 1996. mulch, cantaloupes can produce both this strategy for growing cantaloupes Cantaloupe production in California. UC acceptable yields and sizes even under in situations where aphid-borne virus DANR Pub 7218. 3 p. Jetter KM, Alston JM, Farquharson RJ. heavy pressure from aphid-borne vi- diseases and silverleaf whiteflies are 2001. The case of silverleaf whitefly in Cali- ruses and silverleaf whitefly, without problems. fornia. UC Ag Issues Center. http://aic.ucdavis. multiple applications of insecticide. The edu/oa/whitefly.pdf. Kennedy JS, Day MF, Eastop VF. 1962. A plastic mulch must be present when Conspectus of Aphids as Vectors of Plant the plants emerge from the soil, other- Viruses. London: Commonwealth Institute of wise they may become infected with C.G. Summers is Entomologist, Department Entomology. 114 p. one or more virus diseases while in the of Entomology, UC Davis; J.P. Mitchell is National Weather Service. 2004. http://www.wrh.noaa.gov/Hanford/climo/ cotyledon stage. In our experiments, Extension Specialist, Department of Plant local.shtml. the reflective mulch reduced the land- Sciences, UC Davis; and J.J. Stapleton is In- Prabhaker N, Toscano NC, Henneberry TJ. ing of winged aphids and delayed the tegrated Pest Management Plant Pathologist, 1998. Evaluation of insecticide rotations and incidence of aphid-borne virus diseases UC Kearney Agricultural Center. All authors mixtures as resistance management strategies for Bemisia argentifolii (Homoptera: by 2 to 4 weeks. The reduced incidence are located at the UC Kearney Research and Aleyrodidae). J Econ Entomol 91:820–6. of aphid landing resulted from the Extension Center, Parlier. The UC Statewide Stapleton JJ, Summers CG. 2002. Reflec- reflection of UV light from the mulch IPM Program supported portions of this tive mulches for management of aphids and aphid-borne virus diseases in late-season can- surface. The UV light repels incoming research. We are grateful for the assistance of taloupe (Cucumis melo L. var. cantalupensis). aphids, preventing them from landing Albert S. Newton and Ryan Smith. Crop Protec 21:891–8. and transmitting the viruses. Wheat Summers CG, Mitchell JP, Stapleton JJ. References straw mulch also reflects certain UV 2004a. Management of aphid borne viruses [CMRAB] California Melon Research Advi- and Bemisia argentifolii (Homoptera: Aley- wavelengths, preventing aphids from sory Board. 2003. Pest Management Strategic rodidae) in zucchini squash using UV reflec- landing. Plan — Cantaloupe, Honeydew, and Mixed tive plastic and wheat straw mulches. Environ Both mulches also reduced the inci- Melon Production in California. http://pest- Entomol 33:1644–51. dence and severity of silverleaf whitefly data.ncsu.edu/pmsp/pdf/CAMelon.pdf. Summers CG, Mitchell JP, Stapleton JJ. Elbert A, Nauen R. 2000. Resistance of 2004b. Non-chemical insect and disease colonization. As with winged aphids, Bemisia tabaci (Homoptera: Aleyrodidae) to management in cucurbit production systems. the reflected UV light repels the adult insecticides in southern Spain with special Acta Hort 638:119–25. whitefly, leading to fewer colonizing reference to neonicotinoids. Pesticide Mgt Sci Summers CG, Stapleton JJ. 2002. Use of 56:60–4. UV reflective mulch to delay the colonization adults. This leads to lower numbers of Ferro DN, Mackenzie JD, Margolies DC. and reduce the severity of Bemisia argentifo- immature whiteflies compared with 1980. Effect of mineral oil and a systemic lii (Homoptera: Aleyrodidae) infestations in plants grown over bare soil. insecticide on field spread of aphid-borne cucurbits. Crop Protec 21:921–8. DRAFT94 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 RESEARCH ARTICLE ▼ Large bugs damage pistachio nuts most severely during midseason

Kent M. Daane Glenn Y. Yokota Rodrigo Krugner Shawn A. Steffan Paul G. da Silva Robert H. Beede Walter J. Bentley Gary B. Weinberger ▼

”Large bug” damage to pistachio nuts varies by season, as well as among insect species and development stages, with larger bugs typically causing more damage than smaller bugs. We investigated pistachio damage by three large bug species (leaffooted bug, redshouldered stink bug and flat green stink bug) at different development stages and throughout the season, using field surveys and cage Raksha Malakar-Kuenen, a postdoctoral researcher, whacks a dormant pistachio limb with studies. Before fruit set occurs in June, a mallet to dislodge overwintering stink bugs onto a beating tray, one of the primary field monitoring methods. California pistachios, once considered virtually pest free, are now un- most damaged nuts are dropped from der attack from a variety of insects, especially “true” bugs of the Hemiptera order. the cluster without reducing fruit load. The midseason period (June to July) is the most critical because the Significant crop loss will curs. Early in the season, when the nuts are small (less than 10 millimeters in damaged nuts remain in the cluster. occur only when early-season diameter), feeding punctures through After shell hardening, the kernel is bug densities are so high the fruit pericarp (the outer wall of the largely protected from bug feeding. that the number of dropped nut, comprised of the outer epicarp, the fleshy middle mesocarp and the inner hough once considered virtually nuts exceeds the level endocarp) quickly result in darkened Tpest-free, California pistachios are that the tree will naturally areas of the hull or epicarp lesions now attacked by a variety of insects, compensate. (Uyemoto et al. 1986; Bostock et al. 1987), especially the Hemiptera or true bugs. and the damaged nuts often drop from Most are native pests that built resident the cluster (Purcell and Welter 1991). populations as pistachio orchard acre- bug (Acrosternum hilare [Say]), Uhler’s In midseason, fruit load is set but shell age increased. These pests are com- stink bug and Chlorochroa uhleri (Stål) lignification (hardening) is not complete. monly grouped as “small” and “large” species. All of these bugs use piercing- The damaged nut remains in the cluster bugs. The small bugs (adults about one- sucking mouthparts to feed directly and the resulting epicarp lesion can stain quarter inch) include several species on the nut. While small bugs are often the outer shell, lowering market value. of Miridae and Rhopalidae, most im- abundant and can cause damage early During this time, the kernel is also devel- portantly Calocoris norvegicus (Gmelin), in the season, they pose little threat after oping and feeding punctures can result Phytocoris relativus (Knight) and Lygus shell hardening (Michailides et al. 1987; in necrotic spots on the nut meat (kernel hesperus (Knight). The large bugs (adults Purcell and Welter 1991). Large bugs, necrosis), aborted nuts or fungal contam- about one-half inch) include some spe- on the other hand, have larger, stronger ination (such as stigmatomycosis). cies of leaffooted bugs (Coreidae), such mouthparts and may continue to dam- Therefore, both the bug species pres- as Leptoglossus clypealis (Heidemann); age kernels until harvest time (Michai- ent and the seasonal period will affect and stink bugs (Pentatomidae), such as lides et al. 1987). pest control decisions. We investigated the redshouldered stink bug (Thyanta There are also seasonal differences pistachio damage by three large bug pallidovirens [Stål]), the flat green stink in the type of feeding damage that oc- species (leaffooted bug, redshouldered DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 95 Field guide to pistachio pest insects

Monitoring pistachio orchards is essential to determine the type of insect pest present and the nature of potential damage. Mid- season is the most critical period, but damage can occur early and stink bug and ﬂat green stink bug) late in the season as well. The insects in this guide are among at different development stages and the most common. throughout the season. Our work can improve pest control decisions by de- scribing seasonal periods when large bug feeding results in greater crop loss. LARGE BUGS Pistachio orchard studies Large bugs (adults approximately 1/2 inch |————| ) have larger, stronger mouthparts and may continue to damage kernels until harvest. Field surveys. To compare seasonal changes in nut damage with changes Redshouldered stink bug in pest species, we sampled nine orchards in the San Joaquin Valley in 1998. To sample bugs in the pistachio trees, we took 350 beating-tray samples per orchard every 2 to 3 weeks from April to November. For a beating tray sample, a cloth tray is held under a Small nymph Large nymph Adult* section of the pistachio tree, and when the branch above is struck with a mal- Flat green stink bug let, the dislodged insects are caught on the tray. To sample bugs in the cover crops, we took 350 sweep-net samples per orchard every 1 to 2 weeks from March to September. For this, a cloth insect net was swept through the cover crop, using 50 continuous sweeps while walking through the cover crop for each Small nymph Large nymph Adult bag of collected insects (seven sections Leaffooted bug of each orchard were sampled). Feeding damage was determined by recording the number of epicarp lesions in 700 pistachio nut clusters per orchard every 7 to 14 days from May to September. Cage studies — seasonal damage. In 1998, we conducted cage trials at the UC Kearney Research and Extension Nymphs emerging Medium nymph** Adult** from egg mass Center. After bud-break (when plant dormancy ends), pistachio branches with nut clusters were isolated in 3-gallon All photos by author except *(Jack kelly Clark) and **(Richard E. Rice) Clark) and **(Richard E. kelly All photos by author except *(Jack (11.4-liter) organdy cages. The number of nuts per cluster was recorded, and then a single bug was introduced for a SMALL BUGS 7-day feeding period. After that, the bugs were removed and the numbers of total, Small bugs (adults approximately 1/4 inch |——| ), sometimes called dropped and damaged (epicarp lesion) “plant bugs,” are often more abundant and can cause damage early nuts were recorded. The cages were then in the season. Adults pose little threat after shell hardening. resealed until harvest time, when the numbers of total, dropped and damaged nuts were again recorded. The nuts were then dissected and the kernel condition (clean, necrotic, stigmatomycosis- affected or aborted) was recorded. The trials were conducted at three Calocoris (adult) Lygus bug (adult) Phytocoris (adult) seasonal periods that correspond to changes in fruit susceptibility to bug damage: early season, as the fruit load is

Photos: Jack Kelly Clark Kelly Jack Photos: being set (May 1 to 8); midseason, dur- DRAFT96 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 Pistachio photos: Richard E. Rice Richard E. Pistachio photos:

Above right, Gary Guelce, a research technician at KREC, examines pistachio kernels ing shell hardening (June 10 to 17); and branches were isolated with organdy for evidence of damage. The most critical late season, after shell hardening (Aug. cages, as described. At the beginning period for potential kernel damage occurs 13 to 21). We included the small bug of the season, each cluster has more midseason, when large bug mouthparts can easily penetrate hardening shells. Damaged Calocoris in some of the early trials as a nuts than it will carry to harvest time, kernels may not become apparent until comparable marker to previously pub- and there will be a natural nut drop to harvest. However, generalizing about bugs lished studies. The early-season treat- set the cluster load at about 15 to 20 and nut damage is difficult because of regional and seasonal variations. Damage to ments were adult redshouldered stink nuts per cluster. After the natural nut the interior of the pistachio nut can range bug (RSSB), flat green stink bug (FGSB) drop was nearly complete (May 16), we from blanks, top left, which can be caused and Calocoris. The midseason treatments recorded the number of nuts remain- by large or small bugs early in the season, were adult redshouldered stink bug, ing in the cage and then randomly as- to late season necrosis, bottom left, caused primarily by the larger bugs. flat green stink bug and Calocoris, and signed cages to treatments. the small (second or third instars) and To begin each trial period, a single large (fourth or fifth instars) stages of bug was placed into each cage for a redshouldered stink bug and flat green 7-day feeding period. Every 2 to 3 stink bug. The late-season treatments weeks thereafter, the cages were briefly Statistical analysis. The results were adult redshouldered stink bug, opened and we recorded nut condition are presented as means per treatment flat green stink bug and leaffooted bug, in seven categories: (1) new feeding (± SEM) and compared using analysis and small (second or third instars) and wounds (small puncture with extrud- of variance (ANOVA), with treatment large (fourth or fifth instars) stages of ing fluid), (2) old feeding wound (dried means separated with Tukey’s HSD redshouldered stink bug and flat green puncture, no epicarp lesion), (3) new test. When needed, data were trans- stink bug. We also did a no-insect con- epicarp lesion, (4) old epicarp lesion, formed (√ x) to normalize the variance. trol treatment. For each trial, treatments (5) dropped nuts with bug damage, In the cage study of hidden damage, were set in a complete randomized (6) naturally dropped nuts and (7) no levels of kernel necrosis in each bug block design, with five replicates (cages) damage. We repeated the inoculation treatment were adjusted to the control per treatment (130 cages total). Blocks procedure with new bugs and cages (Abbott 1925). were individual or adjacent trees. every 2 to 3 weeks, for a total of seven Bugs found in field surveys Cage studies — “hidden” damage. trial periods with initial start dates of We call damage after shell hardening May 22, June 8 and 22, July 10 and 26, Overall, insect collections using is complete “hidden,” because epicarp and Aug. 9 and 21. At harvest time the beating tray were low (less than lesions will not form even though some (mid-September), nuts were evaluated 0.2 bugs per sample). In the surveyed of the bug’s probes can successfully for external and internal damage. We orchards, Phytocoris was the most abun- penetrate the shell to feed on the ker- tested redshouldered stink bug, flat dant small bug in the canopy, with three nel. In 2001, we further quantified bug green stink bug and leaffooted bug seasonal peaks in late April, mid-June damage after the midseason period adults and a no-insect control with 10 and late August. Flat green stink bug by inoculating clusters with different cages (replicates) for each treatment was the most common large bug in the bug species every few weeks. Pistachio (210 cages total). canopy and was found from mid-May DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 97 Field studies of pistachio nut damage and drop included a stink bug Fig 1. (A) Average (± SEM) number of small and large bugs collected feeding trial. Bottom, former UC lab assistant Cody Anderson ties from cover crops in nine sampled orchards in the San Joaquin Val- off a 10-gallon organdy cage during dormancy to isolate pistachio ley shows that small bugs, primarily Calocoris, were most common clusters prior to insect damage. Top, former UC staff research associ- early in the season, while large bugs, most commonly stink bugs, ate and study co-author Shawn Steffan opens one of the cages to were most common in June. (B) Average (± SEM) total and damaged inspect midseason nut condition. nuts per cluster in the sampled orchards.

until harvest. Flat green stink bug com- tions in small and large bug species. For more than 24 hours for visibly darkened monly overwinters in the pistachio example, while Neurocolpus longirostris epicarp lesions to form (Bostock et al. orchard and is often the first large bug (Knight) may be one of the more dam- 1987). The result is that insect feeding found each year. We also collected red- aging bugs, it is also rare; and while on nuts in their earliest development shouldered stink bug from July through Uhler’s stink bug may be common in period is easily overlooked. Later, in harvest. There were no leaffooted bugs orchards on the West Side of the San late April and early May as the fruit collected in the beating tray samples; Joaquin Valley, the redshouldered stink load establishes, insect-damaged nuts however, we observed these bugs in the bug and flat green stink bug are more (epicarp lesions) typically remain in the canopy from July through harvest. dominant on the East Side. cluster for a short time. This visible sign From sweep-net samples of the of insect feeding can be used to monitor Nut drop and damage ground covers, we identified 29,873 bug activity. specimens of bug pests. Most bugs were When the nut cluster is formed in The number of visible epicarp lesions collected in spring (fig. 1A), and were April, it has more nuts than it will carry increased in late May and then declined, composed primarily of Calocoris (63%) to harvest. Therefore, the large number leveling off to about four per 100 nuts and Lygus (21%). Large bugs were less of dropped nuts per cluster observed (less than one per cluster) in mid-June common, collected most often in June, in May resulted primarily from a natu- (fig. 1B). In July and August, there was and composed primarily of redshoul- ral drop as fruit load was set (fig. 1B). essentially no change in the number of dered stink bug and flat green stink Nevertheless, there was also an im- lesions (fig. 1B), even though there was bug. The data on the seasonal changes pact from insect feeding. We observed an increase in the number of large bugs in bug species in monitored orchards is Phytocoris and Calocoris feeding on (fig. 1A). This is because insect wounds presented in the following discussion on newly formed nuts in April and most no longer cause epicarp lesions during nut damage. However, it is difficult to of these damaged nuts dropped within fruit maturation and shell lignification generalize about bugs and nut damage 24 hours, without any visible signs of (hardening), when peroxidase activity because of seasonal and regional varia- insect damage. This is because it takes in the pericarp declines (Bostock et al. DRAFT98 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 1987). Therefore, most lesions found after mid-July were the result of earlier feeding wounds. We suggest that the subsequent feeding by large bugs presents potential “hidden” damage, since kernel necrosis may occur without the external sign (epicarp lesion) of insect feeding. Therefore, epicarp lesions cannot be used to monitor insect activity or damage after shell hardening. The relationship between epicarp lesions in pistachio nuts and insect feeding was first reported for the leaffooted bug by Bolkan et al. (1984), and was further clarified for large bugs by Rice et al. (1985) and for small bugs by Uyemoto et al. (1986). Michailides et al. (1987) categorized the seasonal succession of Fig. 2. Average (± SEM) number of epicarp lesions and dropped nuts after a 7-day exposure bug species in a Sacramento County pis- period to different bug species (RSSB = redshouldered stink bug, FGSB = flat green stink tachio orchard and compared damage bug) or development stages, in (A) early season (May 1–8), (B) midseason, during shell hard- levels among bug species. The results ening (June 10–17) and (C) late season, after shell hardening (Aug. 13–21). In each graph, dif- from our field-sampling build upon ferent letters above each bar indicate a significant difference between treatments (Tukey’s HSD test, P < 0.05). these studies and show that the early- season feeding by small and large bugs is minimized because the damaged and dropped nuts will typically not affect fruit load. This results from early-season plant compensation of fruit load (fewer nuts are dropped naturally) in response to insect damage, which was first veri- fied with Phytocoris (Beede et al. 1996). We also confirmed that while large bugs may be present in the orchard after shell hardening is complete, there will not be an increase in epicarp lesions, as first detailed by Bostock et al. (1987). Size and species affect damage Initial damage. After the 7-day feeding period in the cage studies, the numbers of dropped nuts in the early- season trial were higher in all insect treatments other than the control (fig. 2). In the midseason trial, only the adult redshouldered stink bug and adult and large nymph flat green stink bug treatments were significantly higher than the control, and there were no Fig. 3. Average (± SEM) levels of epicarp lesions and internal nut damage (kernel necrosis) treatment differences in the late-season at harvest time for different bug treatments (RSSB = redshouldered stink bug, FGSB = flat trial (fig. 2). The pattern of dropped green stink bug) during (A) early season (May 1–8), (B) midseason, during shell hardening (June 10–17) and (C) late season, after shell hardening (Aug. 13–21). In each graph, different nuts among treatments in the midsea- letters above each bar indicate a significant difference between treatments (Tukey’s HSD son trial also suggests that bug size and test, P < 0.05). One replicate (cage) of the midseason Calocoris treatment was dropped from species affect damage levels. In both the analysis as an outlier. DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 99 ▲ Fig. 4. Amount and type of external nut damage from a leaffooted bug exposed for a 7-day feeding period at mid- and late-season periods (A–F). Arrows indicate the date when the cages were inoculated. Each stacked bar represents averages for the number of nuts that showed the damage sign.

the redshouldered stink bug and flat readily formed)(F = 60.54, df = 2, 12, P green stink bug treatments, dropped < 0.001; F = 12.99, df = 2, 12, P < 0.001; nuts increased from the small nymph respectively). (and Calocoris) to adult stages. Adult In the early-season trial, the number redshouldered stink bug and flat green of epicarp lesions at harvest time was stink bug were tested in each trial quite low (less than 1.5 per cluster) period, and we used changes in these and was similar across all treatments insects’ damage levels to compare (fig. 3). Most damaged nuts dropped seasonal changes. For both the adult from the cluster, as was evident from redshouldered stink bug and flat green collected nuts in the cage bottom with stink bug, significantly more insect- feeding puncture wounds or epi- damaged nuts were dropped in the early- carp lesions. Combined with data on than in the midseason trial, and in dropped nuts (fig. 2), the results sug- the mid- than in the late-season trial gest that most insect-damaged nuts in (F = 14.80, df = 2, 12, P = 0.001; F = 26.00, the early-season period do not remain df = 2, 12, P < 0.001; respectively). in the cluster, verifying there is crop The number of epicarp lesions compensation for early-season damage formed in the early-season trial was by redshouldered stink bug, flat green significantly greater in all insect treat- stink bug and Calocoris. In contrast, in ments than the control, but not different the midseason treatment differences among tested insect species (fig. 2). In in epicarp lesions at harvest time were the midseason trial, bug species and pronounced (fig. 3), with more dam- size had an impact on the formation of age associated with the larger insects. epicarp lesions. As with the number of In the late-season trial, there were no dropped nuts, there were more epicarp treatment differences in the number of lesions in treatments with larger insects, epicarp lesions in the stink bugs tested, with the redshouldered stink bug large while there was a significant difference nymph and adult treatments signifi- in the leaffooted bug treatment. The cantly higher than the control. In the few lesions found may have been the late-season trial there were no treatment result of other pathogens that contami- differences. As with nut drop, differ- nated the insect feeding wounds. ences in the adult redshouldered stink The most critical measure of insect bug and flat green stink bug treatments crop damage in pistachio nuts is kernel were used to compare seasonal periods. necrosis. In the early-season trial, the We found a significant reduction in levels of kernel necrosis were low and epicarp lesions for both adult redshoul- not different among treatments, again a dered stink bug and flat green stink bug result of damaged nuts dropping from in the late-season trial compared to the the cluster (fig. 3). In the mid- and late- early- and midseason trials (F = 7.189, df season trials, there was more damage = 2, 12, P = 0.009; F = 8.80, df = 2, 11, P = in treatments with larger insects, as 0.005; respectively). previously described. Comparing trial Crop damage. At harvest time the periods, kernel necrosis in the redshoul- impact of hemipteran feeding on crop dered stink bug and flat green stink bug damage is more evident. Across the trial treatments was significantly higher in periods, adult redshouldered stink bug the midseason trial than in either the and flat green stink bug feeding resulted early- or late-season trials (F = 11.32, df in significantly more epicarp lesions at = 2, 11, P < 0.001; F = 17.29, df = 2, 11, P harvest time in the midseason trial than < 0.001; respectively). in either the early-season (in which dam- These results for the early- and aged nuts are dropped) or late-season midseason trials are comparable to trial (in which epicarp lesions are not those of previous studies (Michailides DRAFT100 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 Fig. 5. Average (± SEM) levels of epicarp lesions for (A) redshouldered stink bug, (B) flat green stink bug and (C) leaffooted bug were significantly different among different feeding dates. For each insect, different letters above each bar indicate a Fig. 6. Average (± SEM) levels of kernel necrosis for redshouldered significant difference between inoculation stink bug, flat green stink bug and leaffooted bug for different dates (Tukey’s HSD test, P < 0.05). 7-day feeding periods.

et al. 1987; Rice et al. 1985). However, had visibly evident old epicarp lesions) Hidden damage from feeding the results for the late-season trial remained in the cluster until harvest time disagree with those of earlier studies The experiment was designed to (fig. 4A). The pattern of feeding damage on one critical point. While we found better understand the transition period in the second trial (inoculation on June 8) that larger bugs were better able to between the visible signs of feeding was similar to the first trial but had two penetrate the hardened pistachio shell damage (epicarp lesion) and “hid- important differences: there was now lit- and feed on the kernel, we also found den” crop loss (kernel necrosis) in the tle fruit drop, and some of the new feed- significantly less kernel damage in the mid- and late-season periods. Figure 4 ing wounds did not form epicarp lesions late season, suggesting that the hard- shows the amount and type of external due to shell hardening (fig. 4B). ened shell provides some protection nut damage for leaffooted bug; we had The third trial (inoculation on June 22) from even the largest bug tested, adult similar results with redshouldered stink marks a period of considerable change leaffooted bugs. bug and flat green stink bug. in the expression of insect damage. Most Still, there was some kernel damage, As with the previous cage study, the important is that new and old feeding and a comparison of feeding locations seasonal pattern of insect damage pro- wounds did not lead to epicarp lesions for provides an indication of how these vided the most useful information. In many weeks, if at all (fig. 4C). This pattern large bugs are able to penetrate the the first trial (inoculation on May 22), becomes more evident in the fourth, fifth pistachio shell. Michailides et al. (1988) insect feeding quickly resulted in new and sixth trials (figs. 4D, 4E, 4F), when suggest that late-season feeding by the epicarp lesions. The number of new epi- epicarp lesions rarely formed. To illustrate leaffooted bug was successful when carp lesions per cluster was significantly the change in damage levels during the the insect’s mouthparts penetrated the different among tested insects, ranging time when shell hardening is completed, shell near the “Achilles heel” of the pis- from most to least severe in leaffooted we compared the average number of old tachio — the region near the peduncle bug (20.7 ± 1.7), redshouldered stink bug epicarp lesions (those that formed 2 to 4 (the nut’s stem). To test this observa- (8.4 ± 2.1) and flat green stink bug (2.1 weeks after inoculation) across inoculation tion, we regressed the treatment means ± 0.9)(F = 33.58, df = 2, 27, P < 0.001). periods and showed a significant reduc- of kernel necrosis (which indicated that Fruit load was not complete during the tion between the June 8 and 22 inoculation the bug had successfully penetrated the May 22 inoculation period and some of periods for redshouldered stink bug, flat kernel) against epicarp lesions at the the insect-damaged nuts dropped from green stink bug and leaffooted bug (fig. 5). Achilles heel and epicarp lesions else- the cluster, with significantly more nut Levels of kernel necrosis were low where. Indeed, the results confirmed drop per cluster in the leaffooted bug in the May and early-June inoculation that kernel necrosis was significantly (5.3 ± 1.2) than in either redshouldered treatments, with levels increasing in and positively related to epicarp le- stink bug (1.8 ± 0.6) or flat green stink later treatments to a peak in late July, sions at the Achilles heel (y = 3.247x + bug (0.6 ± 0.4)(F = 7.737, df = 2, 27, P = followed by a slight decrease in August 0.610, r2 = 0.93, P < 0.001). 0.002). Most of the damaged nuts (which (fig. 6). We suggest that the lower lev- DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 101 the developing nuts should be monitored for insect damage, and the pistachio canopy and orchard floor should be monitored K.M. Daane is Associate UC Cooperative for small and large bugs. Extension (UCCE) Specialist, and G.Y. The midseason period, as the pista- Yokota, R. Krugner, and S.A. Steffan were chio shell is hardening and the fruit load Staff Research Associates, Division of Insect is set, is the most critical period since the Biology, UC Berkeley (currently, Krugner large bug mouthparts can easily pen- is Graduate Student, UC Riverside, and etrate the shell and most of the damaged Steffan is Project Manager, Utah State nuts remain in the cluster. During this University); P.G. da Silva was Postgradu- period, not all damaged nuts will have ate Student, Division of Insect Biology, UC the externally visible epicarp lesions, and Berkeley (and currently is Associate Profes- some lesions may require up to 2 weeks sor, College of Marin); R.H. Beede is Farm to develop. Therefore, the damaged ker- Advisor, UCCE Kings County; W.J. Bentley nel may not be apparent until harvest, is Areawide Farm Advisor, UC Statewide when nuts are processed and graded. IPM Program, UC Kearney Agricultural In the late-season period when the Center; and G.B. Weinberger is owner, shell has hardened, bug damage was Weinberger & Associates, Visalia. We thank significantly reduced in our studies (but the California Pistachio Commission, UC see Michailides et al. 1987). We suggest Statewide IPM Program and Western Re- that mid- and late-season insect sam- gion SARE program for funding; and Lou- The number of surface lesions to still-soft pling should focus on large bugs in the ise Ferguson, UCCE Specialist, Department pistachio shells can be a good tool for moni- pistachio canopy, especially the adult of Pomology, UC Davis, for technical advice toring insect feeding activity early in the leaffooted bugs, which are most capable with pomology horticulture. Farm managers season. of penetrating the hard pistachio shell. at Sherman Thomas Ranch, Nichols Farm, Therefore, it is helpful to properly iden- Agri-World and Paramount Farms provided tify small and large bugs and monitor field sites. Comments from two anonymous their corresponding damage. reviewers greatly improved the manuscript. Accurately sampling bug densities is difficult. Because reliable sampling References els found in May and June, when the methods and economic action thresh- Abbott WS. 1925. A method for comput- shell hardening is not yet complete, is olds that correlate to economic crop ing the effectiveness of an insecticide. J Econ the result of an increase in aborted nuts loss have not yet been developed, Entomol 18:265–7. (data not provided). Throughout all managers should use a variety of sam- Beede RH, Rice RE, Daane KM, et al. 1996. Relation of Phytocori relativus to lecanium inoculation periods, adult leaffooted pling tools (sweep nets, beating trays scale infestations on pistachios. In: California bugs caused more damage than the and visual inspection) to keep abreast Pistachio Industry Annual Report, Crop Year adult stink bugs tested. As suggested of changes in insect densities. In addi- 1995–96. California Pistachio Commission, Fresno, CA. p 107–18. by Rice et al. (1985) and Michailides et tion, the number of epicarp lesions can Bolkan HA, Ogawa JM, Rice RE, et al. al. (1987), it is clear that adult leaffooted be a good tool for monitoring insect 1984. Leaffooted bug implicated in pistachio bugs can feed on the kernel throughout feeding activity early in the season, epicarp lesion. Cal Ag 38(3-4):16–7. the season. Still, these bugs were caged when lesions may form within 48 Bostock RM, Thomas CS, Ogawa JM, et al. 1987. Relationship of wound-induced peroxi- for 7 days on a single cluster and dam- hours of a wound. However, be more dase activity to epicarp lesion development age levels were less than 20%, and we cautious when monitoring lesions in maturing pistachio fruit. Phytopathol suspect that the hardened shell signifi- during the midseason period, since 77:275–82. cantly reduces insect feeding. there can be a 2-week period between Michailides TJ, Ogawa JM, Rice RE. 1988. Sites of epicarp lesions and kernel necrosis in the initiation of insect feeding and the Practical applications relationship to symptoms and phenology of development of lesions. After shell pistachio fruit. J Econ Entomol 81:1152–4. We showed that in the early-season hardening is complete, insect-dam- Michailides TJ, Rice RE, Ogawa JM. 1987. Succession and significance of several hemip- period, before crop load is set, insect- aged nuts will not be readily visible terans attacking a pistachio orchard. J Econ damaged nuts are dropped from the clus- and when found will indicate feeding Entomol 80:398–406. ter; due to the plant’s natural compensa- that probably occurred weeks or even Purcell M, Welter SC. 1991. Effect of Calo- tion for these dropped nuts, such insect months before. Therefore, insecticide coris norvegicus (Hemiptera: Miridae) on pistachio yields. J Econ Entomol 84:114–9. feeding will not result in crop loss in most applications that target epicarp lesions Rice RE, Uyemoto JK, Ogawa JM, Pem- years and orchards. Significant crop loss may be applied long after the insect berton WM. 1985. New findings on pistachio will occur only when early-season bug damage occurred. For this reason, if problems. Cal Ag 39(1):15–8. Uyemoto JK, Ogawa JM, Rice RE, et al. densities are so high that the number of bugs are found in the orchard after 1986. Role of several true bugs (Hemiptera) dropped nuts exceeds the level for which shell hardening, the best way to assess on incidence and seasonal development of the tree will naturally compensate. For crop damage is to inspect the kernel pistachio fruit epicarp lesion disorder. J Econ this reason, from mid-April through May for signs of insect damage. Entomol 79:395–9. DRAFT102 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 RESEARCH ARTICLE ▼ Early harvest delays berry skin browning of ‘Princess’ table grapes

Pablo M. Vial Carlos H. Crisosto Gayle M. Crisosto ▼

Table grapes commonly suffer from tissue browning during harvest, packing, storage and shelf life, resulting in lower prices and reduced access to markets. We evaluated the development of browning symptoms in ‘Prin- cess’ table grapes. The berries had high skin browning but very low ﬂesh browning incidences. The most skin browning was found in highly mature grapes and appeared after 3 weeks of cold storage. Skin browning was directly related to fruit maturity, but vineyard location had a greater impact on the incidence of skin brown-

ing than maturity. In all locations, the Top and bottom right, fresh-market table grapes are vulnerable to browning of skins skin browning susceptibility of ‘Prin- and flesh during harvesting, packing, storage and shelf life. Research has shown that cess’ table grapes rapidly increased this browning can be reduced in ‘Princess’ table grapes, left, by harvesting when soluble solids range between 16.0% and 18.0%. when the berries reached a titratable acidity of less than or equal to 0.60% cultivar developed and released by the as “internal browning” for ‘Thompson and/or a soluble solids concentration USDA‘s Agricultural Research Service Seedless’. The ‘Princess’ berry browning greater than or equal to 18.0%. Based in 1999 (Ramming 1999). ‘Princess’ symptoms are frequently expressed on on this work, we recommend harvest- resulted from the cross of ‘Crimson white table grape cultivars, including ing ‘Princess’ at a soluble solids con- Seedless’ with ‘B40-208’ in 1988. ‘Italia’, ‘Regal Seedless’ and others. In the centration between 16.0% and 18.0%. ’B40-208’ is a white, seedless selection few cases where internal browning has and is a complex hybrid whose parents been reported on ‘Thompson Seedless’, include ‘Italia’, which is well known the browning started parallel to the vas- able grapes commonly suffer from to exhibit berry browning symptoms. cular system in the center of the berry variations of tissue browning in- According to the California Agricultural and never developed on the skin as it cludingT stem browning (Crisosto et al. Statistics Service, in 2003 there were does in ‘Princess’. 2001), internal flesh browning (Nel- 1,329 acres (325 acres nonbearing) plant- We investigated if the development son 1969) and berry (skin and flesh) ed in the state. In 2000, we conducted a of postharvest berry browning problems browning (Crisosto, Badr, et al. 2002; preliminary postharvest evaluation of in ‘Princess’ was related to cluster ma- Vial 2003) during harvest, packing, ‘Princess’ and observed various berry turity parameters such as soluble solids storage and shelf life. Table grapes browning symptoms similar to those concentration (SSC), titratable acidity that suffer from browning disorders seen in ‘Italia’. (TA), the SSC/TA ratio and juice pH. normally have a shorter postharvest Berry browning occurred either as an Maturity and berry browning shelf life and may not be utilized for irregular shape and scattering on the sur- long-distance markets, which are often face of the berries restricted to the skin, To study the relationship between the most profitable. In general, table which we called “skin browning,” or as grape maturity and berry browning inci- grapes with browning problems garner partial or total browning restricted to the dence, ‘Princess’ table grapes were har- lower prices than grapes without them. flesh, which we called “flesh browning.” vested during the 2001 and 2002 seasons We studied postharvest berry brown- These berry browning symptoms were at three soluble solids concentration (SSC) ing in ’Princess’ (originally known as different from those described in a 1992 ranges: low (13% to 16%), moderate (16% ‘Melissa’), a white, seedless, table grape UC DANR bulletin (Luvisi et al. 1992) to 18%) and high (greater than 18%). DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 103 During the 2001 season, ‘Princess’ table grapes were harvested at three different maturities at California State University, Fresno, from research plots in a vineyard comprised of 6-year-old, cane-pruned vines. ‘Princess’ table grapes were harvested at different maturity levels from three San Joaquin The vines were supported by a wide Valley vineyards. Researchers determined that vineyard location and management practices had a greater influence on tissue browning than maturity in this cultivar. Trellis systems, “V” trellis system, and vine and row nitrogen fertilization, canopy management and rootstocks could play important roles in spacings were 7 feet (2.3 meters) and controlling excess sunlight and hence browning problems. 12 feet (3.7 meters), respectively. A drip irrigation system was installed at planting time in 1996. The entire (2.4 meters) between vines, with drip two-bud spurs and six to eight 15- block received a gibberellic acid (1.0 irrigation; and clusters were tipped bud canes per vine) on a “V” trellis gram per acre) bloom-thinning treat- and the trunks girdled using a 3/8- system. The vineyard was not treated ment at 80% bloom. Standard cultural inch knife immediately after berry set. with gibberellic acid, which is used to practices of irrigation, pest manage- Twelve healthy grapevines were ran- reduce berry set and/or increase size. ment and canopy management were domly selected and labeled at each site The vines were adjusted to similar applied to the entire block. Twelve for the study (Dokoozlian et al. 2001). crop loads (approximately 20 clusters healthy vines were selected and la- In 2002, the ‘Princess’ grapes were per vine). Vine rows were oriented beled for this experiment, with each harvested in Parlier on July 23, Aug. 1 east-west. vine serving as a replicate. Four clus- and Aug. 16; Delano on July 19, July 30, In Arvin, 8-year-old ‘Princess’ vines ters were harvested from each vine on Aug. 12 and Aug. 27; and Arvin on July were grown on Freedom rootstock in July 19, July 27 and Aug. 2, 2001, and 17, July 26 and Aug. 8. sandy loam soil. Vine rows were ori- each cluster was labeled to identify In Parlier, 5-year-old ‘Princess’ ented north-south. Vines were pruned its date of harvest and vine number. vines were grown on their own root- using six to eight 12-bud canes and During the 2002 season, ‘Princess’ stock in fine sandy loam soil. Six trellised to an open gable system. table grapes were harvested at the canes, along with four to six two-bud Gibberellic acid was applied twice. same three levels of maturity from spurs, were retained on each vine at First, 1.5 grams per acre was applied three commercial vineyards located in pruning. Gibberellic acid was applied at 80% bloom to reduce fruit set, then major table grape production regions of at 1 gram per acre near full bloom to 20 grams per acre was applied at fruit the San Joaquin Valley: Parlier (Fresno reduce berry set. Vine rows were ori- set (0.2 to 0.3 inches [6 to 8 mm berry County), Delano (Tulare County) and ented east-west. size]) to increase berry size. Clusters Arvin (Kern County). These vine- In Delano, 8-year-old ‘Princess’ were tipped and the vines were ad- yards were carefully chosen based on vines were grown on their own root- justed to similar crop loads (approxi- their similar age, vigor (moderate to stock in clay loam soil. Vines were mately 35 clusters per vine). high) and management practices. At bilateral-cordon trained and were During both seasons, four clusters all three sites, the spacing was 12 feet pruned using a combination of spurs were harvested from each replica- (3.7 meters) between rows and 8 feet and canes (approximately eight to ten tion (48 clusters per harvest date per location total) on each harvest date. Clusters were harvested in the morn- Table grapes that suffer from browning disorders normally ing (7 a.m. to 10 a.m.) and labeled have a shorter postharvest shelf life and may not be utilized with a code that included the harvest for long-distance markets, which are often the most profitable. date, location, vine number and cluster position. Harvested clusters were placed into plastic boxes with cardboard pads in the bottom to reduce DRAFT104 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 Left, clusters of ‘Princess’ table grapes were harvested between 7 a.m. to 10 a.m., labeled with a code indicating date, location, vine number and cluster position and placed in plastic boxes with cardboard pads. From the vineyards, grapes were taken in an air-conditioned vehicle to the F. Gordon Mitchell Postharvest Center at KREC for visual inspection and analysis, right.

abrasion damage and were immedi- predominant organic acid in grapes. In the 2002 season, clusters from ately transported to the F. Gordon At the same time that these mea- each harvest date were removed from Mitchell Postharvest Center at the surements were taken, labeled clusters cold storage 1, 3, 5 and 7 weeks after UC Kearney Research and Extension from each harvest date were carefully harvest for visual browning evalua- Center in an air-conditioned vehicle. packed using a plastic pad that slowly tions. At 1, 3 and 5 weeks after harvest, released sulfur dioxide (SO ; 7 grams of incidences of berry skin browning and Quality evaluation at harvest 2 sodium metabisulfite)(Tedmark, South flesh browning were visually evalu- During both seasons, each cluster Africa) — combined with a perforated, ated. Flesh browning incidence was the was visually evaluated for skin brown- polyethylene box liner (1/4-inch hole, percentage of clusters with one or more ing upon arrival at the postharvest 3-inch center) — to reduce water loss berries showing symptoms. At about facility. When more than 15% of the and assure Botrytis cinerea control 7 weeks after harvest (7 weeks at 32°F berries were discolored (skin brown- without causing bleaching (Crisosto et [0°C] plus 2 days at 68°F [20°C]), all ber- ing), clusters were considered visually al. 1994). Clusters were placed inside ries were removed and weighed, and unacceptable. After the visual quality a plastic cluster bag and packed in skin browning incidence was expressed evaluation, five berries per cluster were 15.7-by-19.7-inch (40-by-50-centimeter) as a percentage of cluster weight. Flesh carefully removed to determine firm- fiberboard boxes as is done commer- browning and internal browning were ness, soluble solids concentration, ti- cially. The slow release, one-phase also expressed as a percentage of cluster tratable acidity and juice pH (Crisosto, sulfur-dioxide-generating pad was weight after each berry was cut in half Garner, et al. 2002), which are physical used in the top of each box, above the and examined internally. and chemical parameters used to assess cluster plastic bags but inside the box Since harvest dates were different at berry quality. liner. Finally, the boxes were labeled each location, the interaction between These five berries from each repli- and stored at 32°F (0°C) and 80% rela- harvest date and location was not stud- cation were pooled (for a total of 60 tive humidity. ied. In both seasons, harvest date was berries for each set of 12 experimental used independently as a main treatment Storage quality evaluation vines) and pressed through cheese- within each location. Twelve vines were cloth to extract the juice. Soluble In the 2001 season, clusters from the used as replicates and four clusters from solids concentration was measured three harvest dates were removed from each replicate were harvested as experi- with a temperature-compensating cold storage at 12 weeks after harvest mental units. Data analysis was done by refractometer (model ATC-1, Atago for visual browning evaluations. The ANOVA, whereas mean comparison was Co., Tokyo, Japan). Juice titratable number of berries in the sample with carried out by LSD (P < 0.005) using SAS. acidity and undiluted pH were mea- skin browning covering more than 25% Harvest date and maturity sured with an automatic titrator of the berry’s surface was recorded. If (Radiometer, Copenhagen, Denmark) more than 15% of the berries in the sam- In Parlier, there were no significant at a final pH of 8.2 and reported as ple had skin browning, the cluster was differences in soluble solids concen- percentage tartaric acid, which is the deemed “unacceptable” (cull). tration among samples collected on DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 105 the first two harvest dates (17.2% (from 19.2 to 37.5). Juice pH increased TABLE 1. Soluble solids concentration (SSC), titratable acidity (TA), SSC/TA ratio and juice pH and 17.7%), while samples col- significantly between the second and of ‘Princess’ table grapes lected on the third harvest date had third harvest dates (from 3.4 to 3.7). a significantly higher soluble solids Harvesting late resulted in an in- Vineyard location concentration (19.7%) than those col- crease in soluble solids concentration and harvest date SSC/TA (2002) SSC TA* ratio pH lected on the first two dates (table and a reduction in the titratable acid- ...... 1). Titratable acidity decreased sig- ity, thus the SSC/TA ratio increased in Parlier % 7/23 17.2 0.70 24.7 3.2 nificantly between the first and third the mature grapes. 8/1 17.7 0.70 27.8 3.3 harvest dates (from 0.70% to 0.50%). Harvest maturity and storage time 8/16 19.7 0.50 42.1 3.6 The SSC/TA ratio also increased sig- P value < 0.0001 < 0.0001 < 0.0001 <0.0001 nificantly during this period (from In both seasons, skin browning was LSD0.05† 0.6 0.07 3.3 0.045 Delano 24.7 to 42.1), but did not change related to harvest date and in turn, 7/19 13.8 1.00 14.4 N.A significantly between the first two grape maturity, but was very low at 7/30 15.2 0.70 23.1 3.3 sampling dates. Similarly, juice pH harvest for all three maturities. Flesh 8/13 17.0 0.50 36.8 3.5 8/27 18.9 0.40 48.6 3.7 increased between the first and third browning was so low that it was not P value < 0.0001 < 0.0001 < 0.0001 < 0.0001 harvest dates (from 3.2 to 3.6). commercially important (< 2.0%), and

LSD0.05 0.46 0.04 1.74 0.05 In Delano, the soluble solids con- internal browning was not observed at Arvin centration increased significantly be- all. Skin browning was related to grape 7/17 15.6 0.80 19.2 N.A. 7/26 16.6 0.60 27.1 3.4 tween the first and third harvest dates maturity, because after 12 weeks of 8/8 18.4 0.50 37.5 3.7 (from 13.8% to 18.9%)(table 1), as did storage, grapes from the early harvest P value < 0.0001 < 0.0001 < 0.0001 < 0.0001 the SSC/TA ratio (from 14.4 to 48.6). had significantly less skin browning LSD 0.63 0.04 2.29 0.05 0.05 During this period, titratable acidity than grapes harvested later (fig. 1). * Titratable acidity (TA) expressed as tartaric acid. decreased significantly (from 1.00% to Significant changes in skin browning † LSD = least significant difference at the 5% level. 0.05 0.40%). Juice pH increased significantly between the second and third harvest dates (from 3.3 to 3.7). TABLE 2. Skin browning and flesh browning In Arvin, the soluble solids concen- o o after 7 weeks of storage at 32 F (0 C) for tration increased significantly between ‘Princess’ table grape berries the first and third harvest dates (from Location and 15.6% to 18.4%)(table 1). During this harvest date Skin Flesh period, titratable acidity decreased sig- (2002) browning* browning† nificantly (from 0.80% to 0.50%) and the ...... % cull clusters ...... SSC/TA ratio increased significantly Parlier 7/23 0.0 0.1 8/1 23.5 0.5 8/16 58.2 0.8 P value < 0.0001 0.5932

LSD0.05‡ 12.3 1.3 Delano 7/19 0.3 0.1 7/30 3.1 0.0 8/13 33.0 1.0 8/27 55.5 2.0 P value < 0.0001 < 0.0015

LSD0.05 12.6 1.14 Arvin 7/17 0.1 0.3 7/26 0.0 0.3 8/8 14.4 1.0 P value < 0.0001 0.0700

LSD0.05 5.05 0.69 * Clusters with more than 15% discolored (skin browning) berries were considered visually unacceptable (culls). † Percentage of clusters having one or more berries Fig. 1. Relationship between ‘Princess’ table Fig. 2. Relationship between harvest date with ﬂesh browning. Berries were cut longitudinally to grape harvest date and (A) soluble solids and the development of berry skin browning observe ﬂesh browning. concentration (SSC) measured at harvest and in ‘Princess’ table grapes grown in (A) Parlier,

‡ LSD0.05 = least significant difference at the 5% level. (B) skin browning measured after 12 weeks (B) Delano and (C) Arvin, during 5 weeks of of storage at 32ºF (0ºC), 2001 season. storage at 32ºF (0ºC), 2002 season. DRAFT106 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 incidence occurred when the soluble solids concentration increased from about 18% to 19% (fig. 1A). In Parlier, skin browning incidence was low after a week of cold storage, varying from 0% to 10.4% depending on the 2002 harvest date (fig. 2). After 3 weeks, skin browning incidence increased from 6.3% to 31.8%, and after 5 weeks reached 8.3% to 45.8%. Similarly, in Delano the incidence of skin browning was low after a week of cold storage, but increased dramatically after 3 weeks for the second harvest (35%) and reached up to 64.6% after 5 weeks for the fourth harvest. In Arvin, skin browning incidence was Fig. 3. Relationship between harvest date and substantially lower than in Parlier and the development of berry flesh browning in Fig 4. Relationship between ‘Princess’ table ‘Princess’ table grapes grown in (A) Parlier, grape berry skin browning and (A) soluble Delano but followed a similar pattern (B) Delano and (C) Arvin, during 5 weeks of solids concentration (SSC) and (B) titratable of development, increasing with time storage at 32ºF (0ºC), 2002 season. acidity (TA), 2002 season. in cold storage. After 7 weeks in cold storage, skin browning expressed as a percentage of crease significantly during the 2002 after 3 weeks at 32°F (0°C) was directly cull clusters increased significantly in harvest period (table 2). Flesh brown- associated with increases in fruit har- grapes from all three locations (table 2), ing incidence was so low (about half a vest maturity. ‘Princess’ table grapes increasing from the first to the last har- berry per cluster) that it did not have that were harvested at low soluble vests from 0% to 58.2% in Parlier, 0.3% commercial implications and was not solids concentrations exhibited lower to 55.5% in Delano, and 0.1% to 14.4% related to maturity. In general, ’Princess’ skin browning incidence than those in Arvin. Soluble solids concentration, table grapes collected from the three harvested at values above about 18%. SSC/TA ratio and pH were significantly locations in California during the 2002 Skin browning increased sharply when positively correlated with skin browning, season developed skin browning but soluble solids concentration was greater while titratable acidity was significantly not flesh browning during storage. than 16.0% to 18.0% (fig. 4A). High negatively correlated (data not shown). In contrast, our group reported a values of titratable acidity concur with Furthermore, the flesh browning inci- significantly higher flesh browning a low incidence of skin browning, and dence in grapes at all three locations was incidence in 2001 than 2002 (Crisosto, maturity was strongly correlated with low after 3 weeks of cold storage but in- Badr, et al. 2002). The differences can titratable acidity. Grapes harvested at creased dramatically after 5 weeks (fig. 3). be explained by the vineyard condi- titratable acidity values between 0.60% There were no significant differ- tions in the 2002 study, which were and 1.00% showed significantly lower ences between harvest dates in a spe- carefully chosen for vines with well- skin browning incidence than those cific location and the duration of cold balanced vigor and with healthy and harvested at titratable acidity values be- storage, but there was a clear trend shaded canopies. During the 2001 low 0.60% (fig. 4B). The degradation of of increasing flesh browning during season, the ‘Princess’ table grapes organic acids, such as tartaric, citric and storage on a specific harvest date. It were grown in sun-exposed and low- malic, occurred along with fruit matu- is important to note that flesh brown- vigor vineyards and subsequently ration. SSC/TA ratios below 25 were ing during the first 5 weeks of cold showed more browning problems. associated with considerably lower skin storage was measured visually and is Significant development of skin browning than those above 25 (table 1). therefore subjective. However, even in browning occurred during cold stor- However, vineyard location and these evaluations, flesh browning was age of ‘Princess’ table grapes from all management were more important not a major problem and only reached three vineyards. Skin browning was than maturity in tissue browning in a maximum of 12.5% among all loca- observed after 3 weeks in cold storage ‘Princess’ table grapes. There are many tions after 5 weeks in cold storage. and it was strongly correlated with ma- possible reasons for this. First, the phe- After 7 weeks in cold storage, flesh turity. This data agrees with our previ- nolic concentration, type of phenolic browning incidence expressed as a ous work (Crisosto, Badr, et al. 2002), in compounds and polyphenoloxidase percentage of cull clusters did not in- which the incidence of skin browning (PPO) activity vary for the same cultivar DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 107 Davis Krauter

P.M. Vial is Research Associate, C.H. Crisosto is Postharvest Physiologist, and G.M. Crisosto is Staff Research Associate, Department of Plant Sciences, UC Davis, located at the UC Kearney Research and Ex- tension Center, Parlier. We thank Sayed A. Badr, Department of Viticulture and Enol- ogy, California State University, Fresno, for his help and advice on this work.

References Crisosto CH, Badr SA, Garner D, et al. 2002. Screening for orchard factors that influence ‘Princess’ table grapes berry browning during cold storage. Research Report to California Table Grape Commission. Fresno, CA. Crisosto CH, Garner D, Crisosto G. 2002. High carbon dioxide atmospheres affect stored ‘Thompson Seedless’ table grapes. HortScience 37:1074–8. Crisosto CH, Smilanick JL, Dokoozlian NK. 2001. Table grapes suffer water loss, stem browning during cooling delays. Cal Ag Consumers have come to expect unblemished table grapes in the 55(1):39–42. produce section. Postharvest research is helping growers to supply Crisosto CH, Smilanick JL, Dokoozlian N, fresh, attractive produce for the marketplace. Luvisi DA. 1994. Maintaining table grapes post-harvest quality for long distance markets. In: International Symposium on Table among locations, and from year to year skin browning incidence was more im- Grape Production, Anaheim, CA. Am Soc Enol (Sapis et al. 1983). The browning capac- portant than maturity. Flesh browning Viticul. p 95–9. Dokoozlian N, Peacock B, Ebisuda N, Ma- ity for a specific cultivar and among and internal browning incidences were cias A. 2001. Influence of vine training and locations can also be affected by man- not commercially important (< 2.0%). pruning system on ‘Princess’ table grapes, agement practices such as irrigation, The skin browning susceptibility of 2001–02. California Table Grape Commission Viticulture Research Report, Vol XXX. 5 p. fertilization, rootstock, trellis system, ‘Princess’ table grapes increased when Luvisi DA, Shorey H, Smilanick J, et al. pruning systems and canopy manage- berries were harvested at titratable acid- 1992. Sulfur Dioxide Fumigation of Table ment (Sapis et al. 1983; Wissemann and ity levels less than 0.60% and/or soluble Grapes. UC DANR Bull 1932. 21 p. Lee 1981). For example, trellis system, solids concentrations greater than or Nelson KE. 1969. Controlled atmosphere storage of table grapes. Proc Natl CA Res nitrogen fertilization, canopy manage- equal to 16.0%; grapes harvested at an Conf, Michigan State Univ. Hort Rpt 9:69–70. ment and rootstocks could play impor- advanced stage of maturity (> 18.0% Ramming D. 1999. New table grape vari- tant roles in controlling excess sunlight SSC) were more susceptible to tissue eties. Dinuba Table Grape Seminar, Feb. 24, and hence browning problems. browning. To maximize storage poten- 1999. California Table Grape Commission, Fresno, CA. tial and taste, ‘Princess’ grapes should Growing location is important Sapis JC, Macheix JJ, Cordonnier RE. 1983. be harvested at a soluble solids concen- The browning capacity of grapes. II. Brown- Skin browning incidence at harvest tration between 16.0% to 18.0%. ing potential and polyphenol oxidase activities in different mature grape varieties. Am J was low but its level depends on the Skin browning was highly influenced Enol Vitic 34:157–62. level of physical abuse during harvest- by vineyard location or management; Vial P. 2003. Relationship between fruit ing operation. The skin browning in- ‘Princess’ table grapes grown under the maturity and berry browning potential in cidence reached its highest expression specific management conditions of the several table grape cultivars. M.S. thesis, De- partment of Pomology, UC Davis. 68 p. after 3 weeks in cold storage and was plot located in Arvin had two to three Wissemann KW, Lee CY. 1981. Character- strongly related to maturity and vine- times less skin browning incidence than ization of polyphenoloxidase from Ravat 51 yard location. The effect of location on those grown in Delano and Parlier. and Niagara grapes. J Food Sci 46:506–8. DRAFT108 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 RESEARCH ARTICLE ▼ Reduced-risk fungicides help manage brown rot and other fungal diseases of stone fruit

James E. Adaskaveg Helga Förster W. Doug Gubler Jack Kelly Clark Beth L. Teviotdale David F. Thompson ▼

New reduced-risk fungicides are highly effective in managing both pre- and postharvest diseases of stone fruit crops in California, and they have replaced most previously registered materials. These fungicides have a low impact on the environment, high speciﬁcity to target organisms, and low potential for groundwater contamination and human health risks. In stone fruit, they can be successfully used to manage brown rot blossom blight in a new delayed-bloom fungicide application program for low- precipitation years. In our studies, we found that fungicide treatments applied 1 to 14 days before harvest were also effective against preharvest brown rot and protected fruit from fungal decays initiated during harvest. Practices such as mixtures and rotations can be implemented to Project Scientist Helga Förster and Staff Research Associate George Driever run nectarines prevent resistance from developing through an experimental packingline at the F. Gordon Mitchell Post Harvest Center at Kear- and to ensure the lasting efﬁcacy of ney, to evaluate the performance of new reduced-risk fungicides under realistic postharvest conditions. these reduced-risk fungicides.

1996, the U.S. Congress unani- and in turn fewer risks to human health; pesticide discovery and registration mously passed the Food Quality low toxicity to nontarget organisms (Hewitt 1998; Uesugi 1998). INProtection Act (FQPA). Among other (such as bees, birds, fish and plants); At the same time, however, the things, the law formalized the U.S. En- low potential for groundwater contami- ongoing reregistration of older fungi- vironmental Protection Agency’s (EPA) nation; low use rates; and compatibility cides and other pesticides — mandated Reduced-Risk Pesticide Program (initi- with integrated pest management (IPM) by Congress with amendments to the ated in 1993) and mandated that EPA practices (Adaskaveg et al. 2002). Federal Insecticide, Fungicide, and continue to enhance it (EPA 2003, 2004). Concurrently, agrochemical compa- Rodenticide Act (FIFRA) in 1988 — made The FQPA expedited EPA’s review and nies were on the verge of developing a it financially prohibitive for agrochemi- registration decision-making process for plethora of new fungicides and fungi- cal companies to reregister fungicides pesticides that are classified as less risky cide classes, many of which qualified for in the low-profit postharvest market. to human health and the environment reduced-risk status. The simultaneous Postharvest fungicides that were not re- than existing conventional products. The development of these new fungicides registered after 1996 included benomyl advantages of reduced-risk pesticides by several manufacturers was unparal- (Benlate), thiophanate-methyl (Topsin- may include: low mammalian toxicity, leled in the history of fungicide or other M), triforine (Funginex) and iprodione DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 109 Jack Kelly Clark Infections of wounds that occur in the field at harvest are effectively stopped by postharvest treatments, typically done the same day.

(Rovral). Our research goal at the UC residue studies for determining toler- Kearney Research and Extension Center ances or maximum residues on “spe- (KREC) was to evaluate new reduced- cialty” or “minor-use” crops (generally, risk fungicides for potential pre- and those grown on 300,000 acres or less postharvest use on stone fruit crops, in nationwide) such as stone fruit. order to proactively identify effective Several reduced-risk fungicides new fungicides and change the way were included that have extremely low

they can be used. mammalian toxicity (LD50 values from The most important preharvest blos- 2,000 to more than 5,000 milligrams per som and fruit disease of stone fruit kilogram [mg/kg]) and are not known crops in California is brown rot caused or suspected as carcinogens (table 1). by Monilinia fructicola and M. laxa These materials are either derivatives of (Ogawa and English 1991). On fresh- naturally occurring compounds (such as market peaches, plums and nectarines, fludioxonil [Scholar] and pyraclostrobin M. fructicola is the primary cause of [Cabrio]) or were discovered by ran- blossom blight and pre- and postharvest dom chemical synthesis and screening fruit decay. Other diseases caused by for biological activity (such as boscalid the brown rot fungi include green shoot [Endura], fenhexamid [Elevate] and and mature shoot blights. Shoot blights, pyrimethanil [Scala or Penbotec]). We however, only occur in very wet envi- evaluated cyprodinil (Vangard), fenhex- ronments and with high inoculum lev- amid, pyrimethanil and the premixture els. Gray mold caused by Botrytis cinerea of boscalid and pyraclostrobin (Pristine) and Rhizopus rot caused by Rhizopus in preharvest studies, and fludioxonil stolonifer also result in postharvest fruit and all the other compounds except cy- losses every year. Thus, all three of these prodinil in postharvest studies. postharvest decays reduce crop yields For all data reported in the figures, and render commodities unmarketable values followed by the same number (Eckert and Ogawa 1988). are not significantly different based on Our trials with reduced-risk fungi- an analysis of variance and LSD mean- cides at KREC focused on these diseases. separation procedures of SAS version 8.2. This work was done in cooperation Brown rot blossom blight management with fungicide manufacturers and state and federal regulatory agencies includ- While brown rot–infected blossoms ing the Interregional Research Project on the tree rarely reduce crop load sig- No. 4 (IR-4 Project), which conducts nificantly, they are important inoculum

TABLE 1. Conventional and reduced-risk fungicides for management of pre- and postharvest decays of stone fruit

Year of federal registration Common name Trade name Class Rates* Preharvest Postharvest oz. a.i./100 gal Reduced risk Boscalid/pyraclostrobin† Pristine Anilide/strobilurin 5.6 2004 Expected 2005 Cyprodinil Vangard Anilinopyrimidine 3.75, 7.5‡ 2000 Not planned Fenhexamid Elevate Hydroxyanilide 12 2002 2004 Fludioxonil Scholar Phenylpyrrole 4 Not planned 2003 Pyrimethanil Penbotec Anilinopyrimidine 11.4 Expected 2006 Expected 2006 Conventional Dicloran Allisan, Botran Dicarboximide 15.6–27.6 Top above, George Driever inoculates fruit Propiconazole Orbit SBI-triazole 1.8 with an aqueous solution of fungal spores. Tebuconazole§ Elite SBI-triazole 3.6 Above, an untreated control shows obvious * Rates are ounces of active ingredient per 100 gallons of water/acre (preharvest) or 200,000 lbs. fruit (postharvest). signs of a brown rot infection (top), com- † Boscalid and pyraclostrobin (Pristine) are marketed as a premixture. pared with fruit inoculated 14 to 16 hours ‡ Cyprodinil was applied at 3.75 oz. a.i./100 gallons water/acre in the brown rot blossom blight control trial (fig. 1) before fludioxonil treatment (middle) and and at 7.5 oz. a.i./100 gallons water/acre in the preharvest study (fig. 2). fruit inoculated after fludioxonil treatment § Only registered for use on sweet cherry. (bottom). DRAFT110 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 Fig. 1. Efficacy of reduced-risk, delayed-bloom fungicide applications for management of brown rot blossom blight in ‘Elegant Lady’ peaches with natural rain only (0.39 inches in 2003 and 0.79 inches in 2004), and natural rain plus simulated rain. Average of 2003 and 2004 data is shown. Conventional fungicide is shown in red type.

sources for fruit infections. The manage- wet conditions — ment of blossom blight involves integrat- such as high relative ing orchard sanitation with the judicious humidity — which use of fungicides. Important sanitation may occur in practices include the removal of mum- California during mified fruit from trees and orchard wet springs. Without a postharvest fungicide treatment, fruit usually cannot floors after harvest as well as brown rot Similar trends be shipped to distant markets or displayed in the market at shelf cankers during pruning. Previously, UC were obtained for temperatures without risking decay. Commercial, low-volume postharvest fungicide applicators include the “wigwag,” top, and guidelines suggested a two-application all treatments in controlled droplet applicator, bottom, which are among the more program of fungicides at the phenological both years. With popular methods because there is little to no fungicide runoff. blossom stages of pink bud (5% bloom) simulated rain, and full bloom (80% bloom). The current the reduced-risk materials were effec- are mature and rain occurs at harvest updated guidelines (www.ipm.ucdavis. tive in reducing brown rot incidence as time (similar to stone fruit production in edu/PHG) are based in part on the re- compared with the untreated control, high rainfall regions) or improper irriga- search presented here. They indicate that but some of them were more effective tion practices create favorable environ- a delayed, 20% to 40% bloom treatment under ambient conditions (natural rain ments for disease. Decay may develop should be made followed by a second ap- only)(fig. 1). With boscalid/pyraclos- from conidia (spores) contaminating plication at 80% to 100% bloom, if heavy trobin or propiconazole, no disease was fruit surfaces or from recent infections rain or other weather conditions (such as found under simulated or natural rain or quiescent (latent) infections that dense fog and warm temperatures) are conditions. In addition, in years (2001 occur with brown rot and gray mold. conducive to fungal diseases. and 2002) when natural rainfall was low Inoculum from mummified fruit, twig In 2003 and 2004, we compared the ef- during the bloom period, no disease cankers or blighted blossoms commonly ficacy of the new reduced-risk fungicides was detected in any of the treatments contaminates fruit surfaces during the with that of older fungicides (which gen- evaluated in our trials, whereas in the growing season. Quiescent infections erally require higher application rates) in control, 1.5% of the blossoms were dis- (in which the fungus enters plant tissue a stone fruit orchard at KREC. A single eased. Although this blossom blight in- but does not continue to grow or cause delayed-bloom application (20% to 40% cidence may seem low, it is a moderate disease until later) are initiated much full bloom) was done. Although blossom disease level considering the amount of earlier in the season. Growth of the infections could have already occurred at new inoculum that can be produced to pathogen, however, does not continue this bloom stage, our intent was to evalu- contaminate developing fruit in the cur- because fruit are immature and resistant ate the fungicides for their protective rent growing season. The reduced-risk to fungal decay. As fruit ripen, rapid and postinfection activity. In addition to fungicides performed as well as the con- decay may result before or after harvest natural rain (0.39 inches in 2003 and 0.79 ventional products tested, and one ap- even when environmental conditions inches in 2004 during the 2-week bloom plication was enough to reduce brown at harvest time are not conducive to period when the trial was conducted), rot pressure in years when conditions infection. Still, quiescent infections are simulated rain was provided by two were less conducive to disease. considered only a minor cause of fruit high-angle overhead sprinkler irrigations decay in most years (Emery et al. 2000). Preharvest treatments of 6 to 8 hours each, within 5 days after In general, preharvest fungicide treat- fungicide application. This was done to In California’s semiarid climate, ments reduce inoculum (preventing in- find out how treatments would perform brown rot fruit decay before harvest is fections that later sporulate or inhibiting under high rainfall and subsequent mi- generally less severe than postharvest sporulation of existing infections) or pre- croclimate alterations associated with decay of untreated fruit, unless the fruit vent quiescent and active infections on DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 111 fruit before harvest. Furthermore, these the reduced-risk treatments can protect against wound materials (boscalid/ infections that occur during harvesting pyraclostrobin, fen- operations. Fruit injuries may occur from hexamid, cyprodinil contact with plant debris, soil particles and pyrimethanil). or equipment surfaces, or from improper Decay incidence af- handling by harvesters. Preharvest ter wound inocula- fungicide treatments can reduce the inci- tions on unwashed dence of postharvest fruit decay, which fruit was also sig- is especially important when fruit is ex- nificantly reduced Fig. 2. Efficacy of reduced-risk preharvest fungicides to manage natural incidence of brown rot fruit decay. Treatments were applied ported to countries that do not allow the by all treatments using an air-blast sprayer (100 gal/acre) at 14 days and 1 day before use of postharvest fungicides. for both brown rot harvest for ‘Red Diamond’ nectarines, and at 7 days and 1 day be- In all of our evaluations we tried to and gray mold (fig. fore harvest for ‘Elegant Lady’ peaches. Conventional fungicides are simulate standard commercial fruit- 3A), but the efficacy shown in red type. handling practices as closely as possible. of the reduced-risk In general, stone fruit are harvested, materials was generally lower than in still highly active against brown rot. stored and shipped at low temperatures, our studies on the natural incidence of However, cyprodinil and pyrimeth- and then marketed in grocery stores decay. anil were still very effective against and ripened by consumers at ambient In additional studies, preharvest- gray mold decay (fig. 3B). temperatures. Preharvest fungicide treated fruit were washed postharvest These studies on preharvest fungi- applications were evaluated over sev- over a brush bed on an experimental cide applications demonstrated several eral seasons from 2001 to 2003 in ‘Red packingline using chlorine water characteristics of the new group of Diamond’ nectarine and ‘Elegant Lady’ (100 parts per million [ppm] sodium fungicides. First, some of the new fungi- peach orchards at KREC. Treatments hypochlorite), rinsed with plain wa- cides — particularly boscalid/pyraclos- were made at 14 days and 1 day before ter and treated with a postharvest trobin — performed as well as the SBI harvest, or at 7 days and 1 day before fruit coating, again similar to com- materials for managing natural decay. harvest, using an air-blast sprayer mercial practices, and fruit were then SBI fungicides set the standard for effec- calibrated for 100 gallons per acre on wound-inoculated. This washing step tive preharvest treatments of stone fruit four or five single-tree replications for further reduced the efficacy of the after iprodione was cancelled for pre- each treatment in a randomized plot. reduced-risk materials against brown harvest use in 1998. In addition, the new Harvested fruit were evaluated either rot decay, and this was correlated reduced-risk materials generally were for the natural incidence of decay or with a reduction of fungicide resi- less effective when fruit were wounded for decay protection, after we manu- dues in fruit. In contrast, the SBI fun- after treatments, indicating that there ally wounded and inoculated the fruit gicide treatment (tebuconazole) was is little penetration into the fruit and with decay pathogens. For both evaluations, harvested fruit were refrigerated for 1 week at 33°F to 37°F and then transferred to an incubation room maintained at 68°F (approximately room temperature). Fruit were wounded (using a small, beveled-edged nail that simulated a fingernail scratch) and inoculated with conidia of the brown rot fungus (M. fructicola) or gray mold fungus (B. cinerea). In our studies, brown rot was the main natural decay that developed on the incubated fruit. On both stone fruit cultivars, all fungicides evaluated Fig. 3. Efficacy of reduced-risk preharvest fungicide applications for management of brown significantly reduced the incidence of rot and gray mold fruit decay in ‘Elegant Lady’ peaches after wound inoculation. Treatments were applied using an air-blast sprayer (100 gal/acre) at 7 days and 1 day before harvest. decay (fig. 2), including the sterol bio- After harvest, fruit were left (A) unwashed or (B) washed, and waxed on an experimental synthesis inhibiting (SBI) fungicides packingline and wound-inoculated with conidia of either decay fungus. Conventional fungi- (propiconazole and tebuconazole) and cide is shown in red type. DRAFT112 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 Fig. 4. Efficacy of reduced-risk postharvest fungicide applications Fig. 5. Efficacy of reduced-risk postharvest fungicide applica- to manage fruit decays of ‘Red Diamond’ nectarines. Treatments tions to manage fruit decays of ‘Red Diamond’ nectarines. (postinfection, 12 to 14 hours after inoculation; and preinfection, Treatments (postinfection, 12 to 14 hours after inoculation; and before inoculation) were done in a diluted emulsified mineral oil– preinfection, before inoculation) were done in a diluted emulsi- based fruit coating using a low-volume controlled droplet applicator fied mineral oil–based fruit coating using a high-volume T-jet (for rates, see table 1). Conventional fungicide is shown in red type. application system (for rates, see table 1).

demonstrating that these materials are more importantly, during or after har- improve appearance and prevent water mainly wound-protectants. vest. The main goals of a postharvest loss from healthy, ripening fruit. Furthermore, fungicide residues on decay management program are to: Fruit were either: (A) inoculated, the fruit surface can be removed to a avoid fruit injuries, keeping the fruit incubated for 14 hours at 68°F, treated large degree by washing, as shown by healthy and nonsenescent; remove with fungicides and incubated for de- the reduced decay control that we found pathogen inoculum from the surface cay development at 68°F; or (B) treated, in our experiments (fig. 3). Although by sanitation; inhibit the pathogen in inoculated and then incubated. These growers and packers find this less desir- infections that may occur at harvest; schedules were used to obtain infor- able, consumers want less pesticide resi- and protect the fruit from infections mation on the post- (such as wound due on their fruit. Pesticides that have during postharvest handling, ship- protection) and preinfection activity of extremely low mammalian toxicity and ping and marketing. In wet years the fungicides, respectively. We evalu- are easily removed by washing will be conducive to disease, a large portion ated the efficacy of the treatments as the more acceptable to the consumer than of the crop may be destroyed by post- incidence of decay compared with the previously registered products. harvest decay. Without a postharvest untreated control. fungicide treatment, fruit usually can- To control brown rot and gray mold, Postharvest fungicide applications not be shipped over long time peri- fenhexamid, boscalid/pyraclostrobin, Postharvest decay fungi infect ods (2 to 3 weeks) to distant markets pyrimethanil and fludioxonil showed stone fruit tissue through wounds or displayed in the market at shelf excellent activity as postinfection treat- that occur either before harvest or, temperatures without decay developments, while fenhexamid and pyrimeth- ing, making it difficult to ensure anil were not effective against Rhizopus TABLE 2. Efficacy (+++ = most effective that high-quality fruit reaches rot (figs. 4, 5). The efficacy of the fun- to – = ineffective) of conventional and reduced- the consumer (Adaskaveg et al. gicides as preinfection treatments was risk postharvest fungicides as wound-protection 2002). generally lower and inconsistent for treatments of stone fruit Postharvest fungicides were fenhexamid, boscalid/pyraclostrobin evaluated on an experimental pack- and fludioxonil. These fungicides are Brown Gray Rhizopus Fungicide rot mold rot ingline at KREC. This packingline mainly wound-protection treatments Reduced risk includes a brush wash bed, a dry- that are highly effective in preventing Boscalid/ ing area with sponge rollers, and decay from infections when initiated up pyraclostrobin +++ +++ +++ low- and high-volume fungicide to 16 hours before treatment. Infections Fenhexamid ++ +++ – Fludioxonil +++ +++ +++ application equipment over brush of wounds that occur in the field at Pyrimethanil ++ +++ – and roller beds. The setup is similar harvest are effectively stopped by post- Conventional to commercial treatment systems, harvest treatments, typically done the Dicloran + + +++ albeit downscaled. We determined same day. Our data also indicates that Iprodione* +++ +++ +/+++† Tebuconazole‡ +++ ++ + the spectrum of activity of the fun- the new reduced-risk fungicides, par- * Iprodione was cancelled for postharvest use in 1996. gicide treatments, as well as the ticularly boscalid/pyraclostrobin and † Only highly effective against Rhizopus rot when used optimum application methods and fludioxonil, have a spectrum of activity in a fruit coating. compatibilities with the most com- and efficacy comparable to the cancelled ‡ Only registered for use on sweet cherry. monly used fruit coatings, which iprodione (table 2). DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 113 microbial contaminants from growing most important role of the older mate- in the fungicide solution, a sanitizer rials will be their inclusion in resistance must be added and the fruit must be management programs with the newer thoroughly washed before treatment. products. With appropriate strategies, Fludioxonil is particularly suited for this the new reduced-risk tools should be type of application because it is very available for years to come. stable in sodium hypochlorite solutions at 100 parts per million (ppm) active chlorine, while the recirculating application system makes this expensive mate- J.E. Adaskaveg is Associate Professor, and rial more cost-effective. In our studies, H. Förster is Project Scientist, Depart- drench applications were significantly ment of Plant Pathology, UC Riverside; more effective wound-protection treat- W.D. Gubler and B.L. Teviotdale (retired) Fig. 6. Postinfection activity of fludioxonil are Cooperative Extension Specialists, De- treatment (14 to 16 hours after inoculation) ments than low-volume spray applica- to prevent fruit decays of ‘Casselman’ plums, tions (fig. 6). In addition, we observed partment of Plant Pathology, UC Davis; with low-volume controlled droplet applica- that fruit treated with aqueous fungi- and D.F. Thompson is Staff Research As- tions (CDA)(rate is per 10 gallons water, per sociate, UC Riverside. We gratefully ac- 200,000 pounds fruit) on a roller bed, and cide drench applications over a roller drench applications in aqueous solutions bed followed by a CDA application with knowledge George Driever, Staff Research (rates are per 100 gallons water per 200,000 a carnauba-based fruit coating retained Associate, for his contributions to this pounds fruit) followed by CDA, both with study; and appreciate financial support diluted carnauba fruit coating. most of their natural bloom, for a higher market value. from the California Tree Fruit Agreement and agrochemical companies (Arvesta, Resistance management is key BASF, Bayer, Janssen Pharmaceutica and Reduced-risk fungicides have an Syngenta Crop Protection). Application methods compared unparalleled safety profile and are References Postharvest application methods equivalent or superior in their efficacy Adaskaveg JE, Förster H. 1999. Fungicides were evaluated to maximize fungicide to previously and currently registered and their stewardship in a new century of efficacy and minimize disposal issues older fungicides for management of pre- production agriculture. Nut Grower 19:5–7. and postharvest diseases in stone fruit. Adaskaveg JE, Förster H, Sommer NF. and costs. Among the application meth- 2002. Principles of postharvest pathology ods used commercially, low-volume and Cyprodinil, fenhexamid and boscalid/ and management of decays of edible horti- ultra-low-volume controlled droplet pyraclostrobin are fully registered for cultural crops. In: Kader A (ed.). Postharvest applications (CDA; 1 to 25 gallons of preharvest use (table 1). Fludioxonil Technology of Horticultural Crops (4th ed.). UC DANR Pub 3311. Oakland, CA. p 163–95. solution per 200,000 pounds of fruit) are was registered for postharvest use on Eckert JW, Ogawa JM. 1988. The chemical currently the most popular because all stone fruit in 2003. Due to its light- control of postharvest diseases: Deciduous there is little or no fungicide runoff as sensitivity with degradation in ultra- fruits, berries, vegetables and root/tuber violet light and nonpersistence in the crops. Ann Rev Phytopathol 26:433–69. compared with high-volume applica- Emery KM, Michailides TJ, Scherm H. tion methods (generally 100 gallons environment, fludioxonil will not be 2000. Incidence of latent infection of imma- per 200,000 pounds of fruit). Fungicide considered for a preharvest registration. ture peach fruit by Monilinia fructicola and runoff cannot be easily disposed of in Because the new materials belong to relationship to brown rot in Georgia. Plant Dis 84:853–7. the sewer systems of most municipali- different chemical classes with modes [EPA] US Environmental Protection Agency. ties. In peaches and nectarines, the of action different from the older fun- 2004. The Food Quality Protection Act (FQPA) low-volume fungicide treatment can gicides, resistance management pro- Background. www.epa.gov/oppfead1/fqpa/ be applied on a brush bed to the wet, grams can be designed that are based backgrnd.htm (accessed 2/8/05). EPA. 2003. Reducing Pesticide Risk. www. washed fruit, dispersing it evenly over on mixtures and rotations of materi- epa.gov/pesticides/controlling/reducedrisk. the surface. Treating smooth-skinned als (Kendall and Hollomon 1998). In htm (accessed 2/8/05). plums is more problematic because addition, good stewardship of these Hewitt HG. 1998. Fungicides in Crop Pro- single-site mode of action compounds tection. New York: CAB Internat. 221 p. the waxy fruit surface often prevents Kendall SJ, Hollomon DW. 1998. Fungicide sufficient uniform coverage. In addi- should include proper application resistance. In: Hutson D, Miyamoto J (eds.). tion, removal of the waxy bloom on procedures (Adaskaveg and Forster Fungicidal Activity-Chemical and Biological plums by brushing may decrease their 1999) that leave adequate fungicide Approaches to Plant Protection. Chichester, Eng.: J Wiley. p 87–108. desirability in some markets. residues on the fruit and the appropri- Ogawa JM, English H. 1991. Diseases of As an alternative for plums, we eval- ate disposal of fungicide runoff and Temperate Zone Tree Fruit and Nut Crops. UC uated recirculated, high-volume drench fungicide-treated culls. Reduced-risk DANR Pub 3345. Oakland, CA. 461 p. fungicides will not completely replace Uesugi Y. 1998. Fungicide classes: Chem- applications over a roller bed. Although istry, uses and mode of action. In: Hutson D, this method uses a large volume of fun- the older fungicides in the near future, Miyamoto J (eds.). Fungicidal Activity- gicide solution, any runoff is collected but safer chemical control options will Chemical and Biological Approaches to Plant and recirculated for reuse. To prevent be available in many situations. The Protection. Chichester, Eng.: J Wiley. p 23–56. DRAFT114 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 REVIEW ARTICLE ▼ Conventional and molecular assays aid diagnosis of crop diseases and fungicide resistance

Themis J. Michailides David P. Morgan Zhonghua Ma Yong Luo Daniel Felts Mark A. Doster Heraclio Reyes ▼

For the past decade, we have been developing techniques for monitoring pre- and postharvest diseases of tree fruit, nuts and vines at the UC Kearney Research and Extension Cen- ter (KREC). We have also advanced new methods to monitor pathogen resistance to fungicides, which growers can now use to make decisions on disease management. Although accurate, the conventional techniques are time-consuming and only provide results after 5 to 21 days. Molecular methods offer the possibility of faster, more reliable and efficient tests. We have developed such methods to monitor, diagnose and quantify crop pathogens. We have also used these new molecular techniques to answer complex questions on the biology of Kearney scientists, including post-doctoral associate Zhonghua Ma, above, are develop- tree fruit and nut pathogens, the ori- ing advanced diagnostic tools to more quickly and accurately predict pre- and postharvest diseases of tree fruits, nuts and vines. For instance, spore-trap tapes in the field capture gin of their inoculum sources, changes tiny fragments of DNA from airborne fungal spores, which can be identified within hours in in their population structures and the laboratory molecular assays, bottom, while conventional methods require a week or more. epidemiology of the diseases they cause. We are now working on mo- ing season — at harvest and during and how to spray fungicides and which postharvest storage — and to predict resistance-management programs to lecular techniques that could supple- resistance to fungicides. Both conven- employ in the field. ment the conventional ones we have tional and molecular methods can pro- Currently, molecular methodology developed for vine diseases. Private vide powerful decision-making tools for requires costly, specialized reagents diagnostic laboratories have been us- growers, enabling them to predict the and enzymes and expensive special ing a number of these conventional emergence of latent disease, identify the equipment (PCR and RT-PCR ma- techniques and plan to adopt some of sources and structure of fungal popula- chines) and is two or three times more the molecular ones in the near future. tions, and detect the emergence of pes- expensive than the conventional meth- ticide resistance in fungal populations. odology. Presently, none of the specific Although the conventional techniques molecular methods are available to the ur research at the UC Kearney can be accurate and less expensive, only average grower due to prohibitive costs Research and Extension Center minimal information concerning a few and requirements for specialized lab O(KREC) seeks to expand epidemiologi- isolates becomes available 1 to 3 weeks facilities, equipment and specific train- cal knowledge of fungal diseases of after testing. This can be a critical period ing. Nor can UC research laboratories tree fruit, nuts and vines in order to for growers, who must make disease run samples for growers on a fee-per- predict disease risk during the grow- management decisions such as when sample basis. However, when afford- DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 115 ‘Howard Sun’ plum fruit show quiescent (small black specks) and latent (invisible) infections by M. fructicola, to compare conventional and molecular diagnosis techniques. Fig. 1. Linear regression between incidence able, portable molecular instruments Although increasingly accurate of latent infections (ILI) and percentage of branches with fruit rot (PBFR) caused by and simple protocols are developed, weather predictions are available M. fructicola on prune, detected by the ONFIT we expect the routine, accurate and through the National Oceanic and technique. Each dot represents an average quick diagnosis of many crop diseases Atmospheric Administration (NOAA), value of multiple locations and inoculations. to be possible, even in the field. Private other aspects of the disease triangle re- diagnostic laboratories have been quire a large database of information. adopting molecular methods for de- The pathogen’s spore inocula can be tecting and identifying plant diseases, quantified by trapping spores, or predict- itself, environmental conditions, effec- and we recommend that they adopt the ed based on disease incidence in previ- tive cultural manipulations, knowledge methods described here. ous seasons (historical disease data). The of pathogens’ sensitivity to fungicides, For example, we have learned that most susceptible stage of the crop can be and the proper selection and timing of latent infections are correlated with sub- determined experimentally by periodic fungicide sprays. If growers had access sequent disease emergence in the field inoculations with the pathogen. to timely information on the presence of or postharvest. Although conventional In many plant diseases, latency is disease, the structure of fungal popula- methods can detect latent infections, they an important epidemiological stage. tions and the presence of fungal resis- are based upon a 1- to 3-week process In latent infections, the host and para- tance to fungicides, they could make of subjecting infected tissues to tissue- site coexist for a period with minimal correct decisions on resistance manage- damaging agents (such as paraquat) or damage to the host; latency involves ment programs to avoid failures of dis- conditions (freezing), followed by the in- an asymptomatic parasitic phase that ease control in the field or a buildup of cubation of samples. Additionally, there eventually gives rise to visible symp- resistance in the pathogen’s population. are many variations in the type, number, toms if conditions are favorable for Conventional techniques take time duration and sequence of these process- disease development (Verhoeff 1974). If es. Molecular techniques can provide the latent infections are at high levels and The accurate identification and early basis for the efficient, accurate and rapid develop into active symptoms, then a detection of plant pathogens are the cor- detection of pathogen inoculum — and disease epidemic can occur. Latent in- nerstones of successful disease manage- are already being used to supplement fections of grapes, kiwifruit, stone fruit ment. The morphological identification critical conventional methods. and nut crops remain inactive or may of plant pathogens is often difficult and not survive until these fruit start to time-consuming and requires extensive Predicting disease risk mature and environmental conditions knowledge of taxonomy and experience The dynamics of plant disease de- become favorable for disease develop- in recognizing detailed fungal features. velopment include: (1) the absence or ment. In most cases, the incidence of Direct agar plating technique presence and quantity of the pathogen’s latent infections correlates with disease (DAPT). This technique isolates fungal inoculum, (2) the stage and susceptibil- incidence in the field at harvest of tree plant pathogens from symptomatic ity of the crop and (3) the environmental fruit and nut crops (Michailides et al. plant tissues. The agar medium com- conditions that are conducive to disease. 2000) or with the incidence of decays monly used for the DAPT in our labora- These three factors are continuously that develop in storage (Michailides tory is acidified potato dextrose agar changing and make the development and Morgan 1996). (APDA) adjusted to an acid pH of 3.5 of accurate predictive models difficult, The management of tree fruit dis- by amending 2.5 milliliter of lactic acid complex and time-consuming. eases depends on the level of disease (25% strength) per liter of medium. The DRAFT116 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 Kiwifruit

results to determine needs for sorting mold postharvest; and B. dothidea and and repacking fruit, to minimize sec- Alternaria species, which cause blight ondary spread of disease in storage and diseases in pistachio. The test takes to plan for fruit marketing. If growers advantage of the fact that killing the spray only when needed (only vineyards fruit and leaf tissues at a stage when with high incidence of latent infection), they do not favor disease development they reduce cost, increase revenue and triggers the development of latent in- reduce environmental contamination. fections into active disease symptoms The only disadvantage of the technique or accelerates the growth of hidden is that it is time-consuming. plant-tissue colonists. Our laboratory Bud monitoring of Botryosphaeria The conventional BOTMON technique can developed the ONFIT technique as an reveal Botrytis cinerea in sepals of kiwifruit (BUDMON). In the last two decades, alternative to the use of the herbicide plated in Petri dishes containing acidified we have seen more diseases caused by paraquat, which triggers the same potato dextrose agar. Botryosphaeria dothidea. In pistachios events. Freezing and incubation elimi- (Pistacia vera), it caused severe epidem- nate the use of this toxic substance. acid pH is inhibitory to the majority of ics in 1998 with major yield losses. While this is an improvement, the test bacteria, but allows most fungal patho- B. dothidea produces a multitude of still requires up to 7 days (Luo and gens to grow when the Petri plates are spores in flasklike structures (pycnidia) Michailides 2003), during which an or- incubated at 68°F to 77°F (20°C to 25°C) that overwinter on the tree. Rains dur- chard could incur significant damage. for 4 to 7 days. The DAPT can also be ing summer, fall and winter spread the Molecular assays quick, accurate used to isolate latent infections from as- pathogen spores from infected parts ymptomatic fruits and nuts using parts of the trees to newly formed buds. As We have developed several molecu- of tissues and contact areas (Michailides soon as buds develop, B. dothidea can lar methods that can supplement and and Morgan 1997). infest them in latent form, allowing may someday replace the slower con- Botrytis monitoring (BOTMON). them to appear healthy, or can infect ventional techniques. The polymerase This technique detects latent infec- and kill them (Michailides and Morgan chain reaction (PCR), which revolution- tions by Botrytis cinerea of kiwifruit 2004). We developed a technique based ized molecular biology when it was (Actinidia deliciosa) sepals in the field. on DAPT, which is used to reveal latent first described in 1985, has been used The incidence of latent infection is a infections caused by B. dothidea in floral to identify pathogens and determine good predictor of gray mold in cold and vegetative healthy-looking buds of their population structures, taxonomy storage (Michailides and Morgan pistachio (Michailides 1991). Results are and classification. This sophisticated 1996; Michailides and Elmer 2000). available 5 to 7 days after plating and yet increasingly common technol- BOTMON involves the collection of incubation. ogy can definitively determine, for fruit samples with stems attached, Overnight freezing incubation example, whether a piece of plant in- and the removal and plating of sepals technique (ONFIT). This technique is cludes the genetic material of a microbe. or stem ends in APDA. We found that frequently used in our laboratory to Additionally, in the last several years 1 month before harvest is the best time detect and quantify latent infections of we have applied techniques to quantify for sampling immature fruit to perform Monilinia fructicola and Monilinia laxa, pathogen DNA, and these can be very BOTMON and gray mold prediction. which cause brown rot in stone fruit useful to predict disease risk when The results of the colonization of sepals (fig.1); Botrytis cinerea in grapes, which the relationship between quantities of and/or stem ends by B. cinerea become causes bunch rot preharvest and gray pathogens’ DNA in latent infections available 9 days after plating, and growers can use standardized tables to predict Molecular technology increases understanding of the biology the levels of gray mold in cold storage. In California, kiwifruit growers are and population structures of plant pathogens, provides quick increasingly using the BOTMON tech- and accurate answers to epidemiological questions about nique to make decisions on the need for plant diseases, and supports disease-management decisions. preharvest fungicide sprays. Also, packinghouse operators and shippers use the DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 117 Fig. 3. Molecular techniques can detect M. fructicola in (A) plum flowers collected from the field and (B) fruit inoculated with different concentrations of spore suspension of the brown rot pathogen and after various hours of incubation. Fig. 2. (A) A sensitive molecular method (species-specific polymerase chain reaction) that can detect a fentogram (0.000000000000001 gram) of DNA from M. fructicola, the pathogen causing brown rot as conidia and ascospores. Ascospores, requires special training to recognize, in stone fruit. (B) Another molecular technique produced only by M. fructicola, develop count and culture spores, making it im- (nested-PCR) can detect DNA of two spores of in cuplike structures (apothecia). practical for recording the large number the pathogen. The tall column (gel) is a marker (M. fructicola and M. laxa both produce of samples necessary for a large-scale of the known molecular weight, which is used as a reference to quantify the amounts of the conidia; however, conidia are not disease management system. short columns (gels). Base pairs (bp) is a unit produced in apothecia.) The spores PCR-based assays have the potential showing the size of DNA; the larger the bp, disperse in the air and infect blossoms, to monitor airborne inoculum levels the heavier (or longer) the DNA; pg = picogram of plant pathogens because they are (10-12 g); fg = fentogram (10-15 g). causing blossom blight. Subsequently, young fruit can become infected and highly specific and sensitive. Initially, eventually rot. When fruit bearing we developed species-specific prim- latent infections are thinned, they de- ers for the detection of M. fructicola and disease levels has been established. velop numerous conidia — especially in California stone fruits and flowers Many plant pathologists are working under high relative humidity. Conidia (Boehm et al. 2001). And recently, we toward establishing these relationships can disperse and cause additional developed a special PCR (nested-PCR), (the quantity of pathogen DNA to dis- fruit infections in midseason. As fruit which is a very sensitive method for ease levels), especially now when recent matures, a number of latent infections the detection of M. fructicola on spore- advanced technology can quantify the may develop into fruit rot. The inocu- trap tapes (Ma, Luo, et al. 2003). First, pathogens’ DNA in plant tissues with lum potential (amount of a pathogen’s sensitivity tests in the laboratory great accuracy. However, because dis- spores) in orchards is an important showed that the nested-PCR assay ease levels depend on weather condi- factor in blossom blight and fruit infec- could detect the specific DNA piece in tions, it takes several years to establish tion (Luo and Michailides 2001, 2003). as little as 0.000000000000001 gram (or such relationships. These techniques Determining inoculum potential in 10-15 gram) of M. fructicola DNA (fig. could aid in estimating disease potential early- and midseason is critical for pre- 2A) or in DNA from only two spores and levels of latent infections relevant dicting brown rot accurately and man- of M. fructicola (fig. 2B), which is a to disease in the field or during posthar- aging it effectively. much higher degree of sensitivity than vest storage. However, inoculum potential is the was previously possible. However, in a most difficult disease parameter to deter- spore-trap tape sample from the field, Brown rot in stone fruit mine in a stone fruit orchard. Currently, the nested-PCR method can only detect Brown rot, caused by M. fructicola or spore traps are used to determine the 200 or more spores because of various M. laxa, is a destructive disease of stone density of airborne disease agents, in- inhibitors. Using these species-specific fruit (Prunus spp.) in California. The cluding M. fructicola. Because samples primers, we can also detect latent infected mummies of stone fruit harbor from traps require microscopic examina- infections in fruit caused by M. fructi- spores of brown rot pathogens, known tion, this method is time-consuming and cola within hours, while the DAPT or DRAFT118 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 Prune fruit show brown rot symptoms after processing with the Brown rot grows on prune fruit (without freezing) after sterilization overnight freezing incubation technique (ONFIT) and incubating for and incubation with latent infections of M. fructicola 7 days at 74°F (23°C). for 2 to 3 weeks at 74°F (23°C) under 95% relative humidity.

ONFIT would require at least 1 week replace the flower incubation technique Similarly, as expected when visible qui- (table 1). Since the nested-PCR assay (FIT), which provides an estimate of in- escent infections were used, 60.5% were cannot quantify the exact number of M. oculum potential in stone fruit orchards positive for M. fructicola with the PCR fructicola spores on a spore-trap tape, in about 4 to 5 days. technique and 54.3% of those plated on we are now working on a real-time In a second experiment conducted APDA developed colonies of M. fructi- (RT)-PCR technique that can do so. in an orchard with ‘Howard Sun’ cola. Most importantly, the traditional Comparison of methods. In March plums, the presence of numerous vis- techniques required 5 to 9 days while and April 2001, hundreds of flowers of ible quiescent infections suggested the the PCR technique provided the results ‘Royal Diamond’ plum were collected presence of even more latent (invisible) within only 30 hours (table 1). from a commercial orchard in Reedley, brown rot infections. We decided to Pistachio fungi inoculum sources Calif. A subsample of 30 flowers was compare the DAPT of visible quiescent divided into three groups based on vi- infections with the ONFIT of invisible As the pistachio industry in sual symptoms: flowers heavily infected latent infections and a species-specific California has matured, fungal diseases with M. fructicola and showing obvious PCR technique. In mid-May, fruit were have become a major threat, some- signs of fungal sporulation on the stem observed in the field, and their fruit-to- times causing significant losses. One of and calyx surface, and designated (+); fruit contact surfaces were marked with these diseases, panicle and shoot blight flowers displaying brown patches on a permanent pen. All these fruit were caused by B. dothidea, was recorded for the petals but no external signs of fun- then collected and brought to our KREC the first time in summer 1984 in a com- gal sporulation (+/−); and flowers with- laboratory, surface-disinfected in 10% mercial orchard in Butte County. This out any evidence of brown discoloration bleach solution for 3 minutes, rinsed disease infects shoots, branched flower or fungal infection (−). Using these flow- with sterile water twice, and placed on clusters, leaves and panicles throughout ers, the PCR detected the DNA of M. clean paper towels. The fruit samples the season. By 1999, it had spread to fructicola in all (100%) of the (+) flowers, were split into three subsamples. pistachio orchards throughout the state, 80% of the (+/−) and only in 10% of the Using the PCR technique, 7.9% of the causing yield losses of 40% to 100% (−) flowers (fig. 3A). samples with invisible latent infections (Michailides and Morgan 2004). These results were confirmed as ac- were positive for DNA of M. fructicola, B. dothidea has been recovered from curate by plating (on APDA) another and 6.7% of the fruit processed with more than 35 native and introduced plant subsample of 30 flowers, providing a ONFIT developed brown rot (table 1). species (Michailides and Morgan 2004), potentially useful method for assess- suggesting that these hosts may serve as

ing disease risk and blossom blight TABLE 1. Techniques to detect Monilinia fructicola in inoculum sources and threaten com- incidence and developing pre- and ‘Howard Sun’ plums mercial plantings, since pistachio was postharvest chemical control strate- only recently (early 1970s) introduced gies against brown rot. This study Latent Quiescent as a commercial crop in California. took about 8 hours for collecting and infections infections Time required In greenhouse and field inoculation Technique (invisible) (visible symptoms) for results testing the flowers. However, results tests, we found that all B. dothidea iso- ...... % ...... days from the plating of flowers became PCR 7.9 60.5 1.25* lates recovered from other hosts were available after 4 days. Private labora- ONFIT 6.7 — 7–9 capable of infecting pistachio. tories could take this technology and DAPT — 54.3 5–7 Although multiple applications offer it to growers right now. The * Time includes 1-day preincubation of sample. of the new strobilurin fungicides PCR technique could supplement or have provided excellent control of DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 119 TABLE 2. Resistance to fungicides in some pathogens of California tree fruit, nuts and vines detected by the plating or molecular assays

Pathogen Fungicide (category) Resistance detected Monilinia fructicola Benomyl, thiophanate-methyl (benzimidazoles) Yes M. laxa Benomyl, thiophanate-methyl (benzimidazoles) Yes Botryosphaeria dothidea Benomyl, thiophanate-methyl (benzimidazoles); No iprodione (dicarboximide); Yes* azoxystrobin (strobilurin) No Fusarium moniliforme Benomyl (benzimidazole) Yes Botrytis cinerea Benomyl, thiophanate-methyl (benzimidazoles); Yes fenhexamid (hydroxyanilide) Yes* Alternaria alternata, Azoxystrobin, pyraclostrobin, A. tenuissima, A. arborescens triﬂoxystrobin (strobilurins); Yes iprodione (dicarboximide) Yes* * Laboratory-induced resistance only.

the disease in recent years, the potential potential inoculum sources for panicle development of fungicide resistance in and shoot blight of pistachio (fig. 4). B. dothidea is a significant concern. The (Forensic science uses similar DNA use of resistant pistachio cultivars is the fingerprinting techniques in criminal ultimate goal of any disease manage- investigations.) ment program, but the judicious devel- Nonpistachio hosts. Although opment and deployment of resistant B. dothidea obtained from California cultivars depends on the population pistachio are primarily asexual and Fig. 4. DNA fingerprints of B. dothidea isolates (the pathogen causing panicle structure of the pathogen. To improve very homogeneous, relatively high and shoot blight of pistachio) collected understanding of the pathogen’s ge- levels of genetic diversity were ob- from hosts at different locations in California netic diversity and how it has changed served in B. dothidea isolates collected counties (shown in parentheses) and Greece. over the years at diverse locations, we from nonpistachio hosts (fig. 5). These conducted several studies that will can infect pistachio. Consequently, if eventually advance pistachio breeding we are to select durable disease-resis- programs (Ma et al. 2004). tant cultivars these cultivars should Genetic variation. The genetic be tested with B. dothidea isolates that makeup of B. dothidea populations has represent various genotypes from both remained homogeneous since it was pistachio and nonpistachio hosts. first detected in 1984. We took samples Monitoring fungicide resistance of B. dothidea from infected pistachio orchards at diverse locations, some Fungicides are commonly used to more than 600 miles (960 kilometers) manage plant diseases. However, the apart, and over the course of several frequent use of fungicides with a single years. Our findings, as well as the mode of action incurs a high risk of pathogen’s lack of propensity to form selecting resistant genotypes of plant a sexual stage on this host, suggest pathogens. To determine levels of resis- that a program to breed resistant pis- tance to fungicides, the most common tachio cultivars has a high chance of traditional technique is direct-plating success. However, the interactions of a single-spore isolates in media amended genetically uniform yet highly virulent with various concentrations of fun- Fig. 5. Genetic variation within populations pathogen population and the monocul- gicides and determining inhibition of B. dothidea from pistachio and other hosts ture of the highly susceptible pistachio of growth and/or spore germination next to a pistachio orchard in Glenn County. The taller the bar, the larger the genetic varia- cultivars (‘Kerman’ and ‘Peters’) still (table 2). The entire test can take 1 to tion of isolates. Scale is from 0 to 1, where pose a serious threat to the California 3 weeks — longer if the time required 0 = no variation and 1 = entirely (100%) dif- pistachio industry. to isolate the pathogen from infected ferent (1/5th of full scale is shown). DNA fingerprints. The DNA finger- plant tissues is included. This conven- prints of B. dothidea isolates collected tional technique is time-consuming but from pistachio were identical to those critical, since growers rely on the re- of some B. dothidea isolates collected sults to decide on fungicide programs from other hosts (Ma et al. 2001), for their orchards. which suggests that native and intro- In 2004, a new technique was report- duced hosts for B. dothidea, other than ed using the spiral plate gradient- pistachio, have historically served as dilution method. Though an improve- DRAFT120 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 ment, the method still requires 1 to 5 days for mycelial growth assays, followed by 14 to 20 hours for the spore inhibition studies to reveal results, plus 2 to 5 days for sporulation of fungi in culture (Förster et al. 2004). DNA assays for fungal resistance Strobilurin resistance. Alternaria late blight caused by Alternaria spp. in the alternata, tenuissima and arborescens species-groups (Pryor and Michailides 2002) is one of the most common fungal diseases of pistachio in California, and affects foliage and fruit. The disease can cause severe premature defoliation, staining of nutshells and molding of the kernels, which reduce fruit qual- Fig. 6. (A) A change (mutation) in a specific ity. Controlling Alternaria late blight gene of Alternaria spp. helps distinguish azoxystrobin-sensitive from azoxystrobin- requires a combination of cultural prac- resistant Alternaria isolates from pistachio; tices (irrigation management and prun- (B) A specific molecular technique (allele- Surface sterilization of immature prune ing to reduce humidity) and multiple specific PCR assay) can detect azoxystrobin- fruit with latent infections by M. fructicola fungicide sprays. resistant Alternaria form lesions on pistachio is conducted by UC San Diego undergradu- leaves infected only by azoxystrobin- ate Bobby Koja, by placing it in a contain- The strobilurin fungicide azoxy- resistant and not by azoxystrobin-sensitive er for the overnight freezing incubation strobin (Abound) provided excellent Alternaria isolates. technique (ONFIT). efficacy against this pistachio disease for some years. However, azoxystrobin- resistant populations of Alternaria have the growth stage of the pathogen, and Since the PCR-RFLP assay requires been detected in a fungicide experimen- not influenced by the environment. If two steps and is still time-consuming tal orchard and commercial pistachio a DNA marker linkage with fungicide if a larger sample must be tested, we orchards after multiple sprays for only resistance is established (identification further developed a one-step, allele- 3 to 4 years, which caused failures of of the mechanism of resistance), it can specific PCR (AS-PCR) method to disease control in the field (Ma, Felts, be used to detect fungicide resistance in rapidly detect azoxystrobin-resistant et al. 2003). natural fungal populations. Alternaria in pistachios (Ma and Because azoxystrobin-resistant In 2003, we found that azoxystrobin Michailides 2004a). This AS-PCR method Alternaria populations appeared rapidly resistance in Alternaria from pistachio is being used in our laboratory now in pistachio orchards, it became urgent was correlated with a single-point mu- to rapidly detect the percentage of le- to incorporate effective antiresistance tation in the mitochondrial cytochrome sions caused by azoxystrobin-resistant strategies when this or other strobilurins b gene (Ma, Felts et al. 2003). Based on Alternaria, making the results available (because of cross-resistance) were used this mutation, we developed a PCR to the grower within a day. to control Alternaria late blight. The restriction fragment length polymor- The AS-PCR assay was not quan- first important step is determining the phism (PCR-RFLP) marker that detects titative per se and only detected the sensitivities of pathogen populations to DNA only from azoxystrobin-resistant presence of azoxystrobin-resistant fungicides. Using the current conven- isolates of Alternaria, but not from Alternaria. However, after purchasing tional method, one person can examine azoxystrobin-sensitive isolates (fig. a real time (RT)-PCR machine, the only about 30 isolates in 2 work days, 6A). Using this molecular method, one new RT-PCR technique can be used assuming that mature Alternaria spores person can examine as many as 100 to accurately determine the frequency are available for plating in fungicide- samples in a workday. Because many of azoxystrobin-resistant Alternaria amended media. Obtaining spores samples can be processed in a day, the isolates. Because 96 samples can be requires 4 to 5 days for the incubation cost for this test is not prohibitive. In run simultaneously by the RT-PCR of cultures at optimum growth tempera- fact, it is ready to be offered by private machine, the method is not expensive tures. It is almost impossible to produce diagnostic laboratories that are willing and is ready to be used by private results in a timely fashion. to adopt and offer this new procedure diagnostic laboratories. However, a Molecular markers by their poten- (based on protocols provided by our private lab has to first buy the expen- tial nature are stable, not specific to UC laboratory). sive RT-PCR machine (about $35,000). DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 121 Above, apothecia of M. fructicola as observed in the field and right, blossom blight in prunes caused by M. fructicola. New molecular technology can help growers to detect and better manage resistance to fungicides.

Larger laboratories are equipped with This technique used blossoms collected noticed that azoxystrobin had failed to RT-PCR machines, and we expect that from peaches and almonds in March control Alternaria late blight in his fields. within a few years smaller laborato- 2004 and successfully detected the Within 2 days of collecting Alternaria ries will adopt this technique. level of resistance to benzimidazole in isolates from leaf lesions in his field, Based on the AS-PCR assay de- M. fructicola (peaches) and in M. laxa we cautioned that 80% of the Alternaria scribed above, we developed an allele- (almonds). These protocols are avail- isolates were resistant to azoxystrobin specific, real-time PCR assay to quantify able to private diagnostic laboratories, and cross-resistant to other registered the amount of azoxystrobin-resistant which are free to use the techniques at strobilurins. The grower avoided using Alternaria DNA in a sample extracted any time. Obviously, such rapid and any additional strobilurin sprays and from disease lesions (such as 50 disease quantitative detections of fungicide re- instead he used chlorothalonil, which lesions collected from a commercial pista- sistance in the fungal pathogen popu- has a wide mode of action. chio orchard)(Ma and Michailides 2004b). lations will be valuable for California Future goals of our research are to Using this method, we can now detect growers to manage fungicide resistance develop techniques that can supple- frequencies of azoxystrobin-resistant in stone fruit and almond orchards, ment or replace DAPT, BOTMON, Alternaria populations from at least 60 or- especially since the benzimidazole fun- BUDMON, FIT (flower incubation chards (50 disease lesions per orchard) in gicide thiophanate methyl (Topsin-M technique) and the conventional quan- 2 work days, while the conventional spore 70WP) is still registered and recom- tification of pathogen inoculum using germination technique would require at mended by the UC disease manage- spore traps in orchards and vineyards, least 200 work days for processing the ment guidelines to control brown rot with efficient, accurate and rapid mo- same number of samples/isolates. diseases in stone fruit and almonds. lecular procedures using RT-PCR. In Benzimidazole resistance. Since the near future, we plan to emphasize Future prospects benzimidazole resistance in M. fructi- research on molecular techniques to cola and M. laxa has been shown to be In general, molecular technol- provide results more quickly than the genetically related to point mutations ogy increases understanding of the BOTMON and BUDMON techniques, in the β-tubulin gene (Ma, Yoshimura, biology and population structures of especially since we have good evi- et al. 2003), we developed an allele- plant pathogens, provides quick and dence of the quantitative relationships specific RT-PCR method for rapidly accurate answers to epidemiological of BOTMON with gray mold in cold detecting benzimidazole-resistant questions about plant diseases, speeds storage and BUDMON with panicle M. fructicola in stone fruit and M. up fungicide-resistance detection, and and shoot blight of pistachio in the laxa isolates in almonds, in a manner supports disease-management deci- field. Furthermore, the goal of our similar to that used for the detection of sions. For example, in summer 2002 laboratory is to reduce the cost of pro- Alternaria resistance to azoxystrobin. a pistachio grower in Kern County tocols that incorporate molecular tech- DRAFT122 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 Right, symptoms of severe Alternaria late blight in pistachio; below right, leaf lesions caused by Alternaria isolates are used to determine the incidence of azoxystrobin-resistant isolates of Al- ternaria species. Below, pistachios severely infected with panicle and shoot blight caused by Botryosphaeria dothidea; DNA fingerprints of the fungus collected from pistachio and other hosts suggest that nonpistachio hosts serve as inoculum for the disease.

resistant Alternaria populations from pis- niques, by developing the capacity to References tachio orchards in California. Crop Protec process large numbers of samples at Boehm EWA, Ma Z, Michailides TJ. 2001. 23:1259–63. our laboratory and providing the pro- Species-specific detection of Monilinia fructi- Ma Z, Yoshimura MA, Michailides TJ. tocols to private laboratories. cola from California stone fruits and flowers. 2003. Identification and characterization of Phytopath 91:428–39. benzimidazole resistance in Monilinia fructi- Förster H, Kanetis L, Adaskaveg JE. 2004. cola from stone fruit orchards in California. Spiral gradient dilution, a rapid method for Appl Env Microbiol 69:7145–52. determining growth responses and 50% ef- Michailides TJ. 1991. Pathogenicity, distribution, sources of inoculum, and infection T.J. Michailides is Plant Pathologist, D.P. fective concentration values in fungus- fungicide interactions. Phytopath 94:163–70. courts of Botryosphaeria dothidea on pista- Morgan is Staff Research Associate, Z. Ma is Luo Y, Michailides TJ. 2001. Factors affect- chio. Phytopath 81:566–73. Postdoctoral Research Associate, Y. Luo ing latent infection of prune fruit by Mon- Michailides TJ, Elmer PAG. 2000. Botrytis is Associate Project Scientist, D. Felts ilinia fructicola. Phytopath 91:864–72. gray mold of kiwifruit caused by Botrytis ci- Luo Y, Michailides TJ. 2003. Threshold nerea in the United States and New Zealand. is Laboratory Assistant, M.A. Doster is conditions that lead latent infection to prune Plant Dis 84:208–23. Staff Research Associate, and H. Reyes is fruit rot caused by Monilinia fructicola. Phy- Michailides TJ, Morgan DP. 1996. Using in- Laboratory Assistant, Department of Plant topath 93:102–11. cidence of Botrytis cinerea in kiwifruit sepals Pathology, UC Davis, located at the UC Ma Z, Boehm EWA, Luo Y, Michailides TJ. and receptacles to predict gray mold decay in 2001. Population structure of Botryosphaeria storage. Plant Dis 80:248–54. Kearney Research and Extension Center, dothidea from pistachio and other hosts in Michailides TJ, Morgan DP. 1997. Influ- Parlier. The authors are grateful for fund- California. Phytopath 91:665–72. ence of fruit-to-fruit contact on the sus- ing from the California Apple Commission, Ma Z, Felts D, Michailides TJ. 2003. Resis- ceptibility of French prune to infection by tance to azoxystrobin in Alternaria isolates Monilinia fructicola. Plant Dis 81:1416–24. California Kiwifruit Commission, California from pistachio in California. Pesticide Bio- Michailides TJ, Morgan DP. 2004. Panicle Pistachio Commission, California Dried chem Physiol 77:66–4. and Shoot Blight of Pistachio: A Major Threat Plum Board, California Tree Fruit Agree- Ma Z, Luo Y, Michailides TJ. 2003. Nested to the California Pistachio Industry. American ment, California Table Grape Commission, PCR assays for detection of Monilinia fructi- Phytopathological Society, St. Paul, MN. www. cola in stone fruit orchards and Botryosphae- apsnet.org/online/feature/pistachio/. California Fig Institute, U.S. Department of ria dothidea from pistachios in California. J Michailides TJ, Morgan DP, Felts D. 2000. Agriculture (award no. 2002-51100-01990), Phytopath 151:312–22. Detection and significance of symptomless UC Specialty Crop Research Program Ma Z, Luo Y, Michailides TJ. 2004. Spatio- latent infection of Monilinia fructicola in California stone fruits. (Abstr.) Phytopath 90: (project no. SA6677) and Biotechnology temporal changes in the population structure of Botryosphaeria dothidea from California S53. (BioSTAR)(Bio99-10054 and Bio99-10054F2 pistachio orchards. Phytopath 94:326–32. Pryor BM, Michailides TJ. 2002. Morpho- grants). The authors thank Eric Boehm, Ma Z, Michailides TJ. 2004a. An allele- logical, pathogenic, and molecular character- Barry Pryor, Rebbekah Morgan, Kevin Tsuda specific PCR assay for detecting azoxystrobin- ization of Alternaria isolates associated with resistant Alternaria isolates from pistachio in Alternaria late blight of pistachio. Phytopath and Kevin Robertson for technical assistance. California. J Phytopath 152:118–21. 92:406–16. The protocols for methods described in this Ma Z, Michailides TJ. 2004b. A real-time Verhoeff K. 1974. Latent infections by article are available upon request. PCR assay for the detection of azoxystrobin- fungi. Annual Rev Phytopathol 12:99–107. DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 123 REVIEW ARTICLE ▼ Deep vadose zone hydrology demonstrates fate of nitrate in eastern San Joaquin Valley

Thomas Harter Yuksel S. Onsoy Katrin Heeren Michelle Denton Gary Weissmann Jan W. Hopmans William R. Horwath ▼

The sustainability of water resources is key to continued prosperity in the San Joaquin Valley and California. The vadose zone is an often-ignored layer of wet but unsaturated sediments between the land surface and the water table. It plays an important role in groundwater recharge and Nearly 3,000 feet of continuous soil cores were obtained between July and October 1997 us- in controlling the flux and attenua- ing the Geoprobe direct-push drilling method. This method allowed for complete recovery of tion of nitrate and other potential undisturbed cores throughout the 52-foot deep vadose zone. Above, UC Davis vadose zone hydrology professor Jan Hopmans (left) and Fresno State geology undergraduate Anthony groundwater contaminants. In a Cole operate the coring equipment. former orchard at the UC Kearney Re- search and Extension Center, we in- when the Clean Water Act, the Safe refer to the unsaturated zone above the vestigated the processes that control Drinking Water Act, the Federal Insec- water table as the vadose zone. In gen- the movement of water, nitrate and ticide, Fungicide, and Rodenticide Act eral, only the uppermost 4 to 6 feet (1 other contaminants through the deep and other legislation related to water to 2 meters) is described in soil surveys pollution were enacted. Since then, and investigated in soil studies; the vadose zone. These processes were countless efforts have been mounted deep vadose zone below the root zone found to be controlled by the alluvial by both the scientific-technical commu- remains largely outside the area of re- sedimentary geology of the vadose nity and the agricultural industry to bet- search and regulatory activity. zone, which is highly heterogeneous. ter understand the role of agricultural Yet, the vadose zone below the This heterogeneity should be consid- practices in determining the fate of fer- root zone stores significant moisture. ered when interpreting soil and deep tilizer and pesticides in watersheds (in- All water and contaminant transport vadose zone monitoring data and cluding groundwater) and to improve from the land surface to groundwater assessing of the leaching potential of agricultural management accordingly. passes downward through the vadose Much of the scientific work related to zone. Few studies have investigated agricultural chemicals. The transport subsurface nitrate and pesticide leach- the fate or potential fate of, for ex- of contaminants through the vadose ing has focused on two areas: docu- ample, nitrate and other contaminants zone may be significantly faster than menting the extent of contamination in in such deep vadose zones. Key ques- previously assumed, while denitrifi- groundwater; and investigating the fate tions include, What is the time of cation is likely limited or insignificant of these chemicals in the soil root zone travel through the deep vadose zone? in the oxic, alluvial vadose zone of (including the potential for groundwa- And, is there significant denitrification the eastern San Joaquin Valley. ter leaching) as it relates to particular (natural attenuation) of nitrate in the agricultural crops and management deep vadose zone? practices. Rarely are these two research Pioneering work on nitrate in deep or decades, the leaching of agricul- areas linked within a single study. soil profiles was presented by Pratt et al. tural chemicals (fertilizer, especially In California’s valleys and basins, (1972) who investigated nitrate profiles nitrate,F and pesticides) has been a particularly in Central and Southern in a Southern California citrus orchard concern of agronomists, soil scientists California, groundwater levels are fre- to depths of 100 feet (30 meters); they and hydrologists. Federal legislation quently much deeper than 10 feet (3 estimated that it would take between 10 first recognized the potential impacts meters) and sometimes as deep as 150 and 50 years for nitrate to leach to that to water resources in the early 1970s, feet (45 meters) or more. Hydrologists depth. Average nitrate-nitrogen levels DRAFT124 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 Preferential flow paths, which are responsible for most of the water and solute transport from the root zone to the water table, quickly flush nitrogen to deeper portions of the vadose zone and to the water table, allowing for little or no denitrification.

below the root zone varied from 15 to 35 subplots (0, 100 and 325 pounds per in the three subplots. The analysis milligrams per liter (mg/L) under a acre) were selected in 1997 (2 years showed that the annual nitrogen leach- 50 pounds per acre (lb/ac) treatment after termination of the experiment), ing of excess nitrogen fertilizer from and from 35 to 55 mg/L under an exces- which we refer to as the control, stan- the root zone into the deep vadose sive 350 lb/ac treatment. Based on gross dard and high subplot, respectively. zone was 51 (± 19), 83 (± 30) and 245 mass-balance estimates, denitrification To start, we conducted a conventional (± 42) pounds per acre. Water losses at that site was estimated to account for root-zone nitrogen (N) mass-balance from the root zone to the deep vadose up to 50% of nitrate losses in the thick analysis from application and harvest zone in the flood-irrigated orchard unsaturated zone profile where applica- records for the 12-year experiment amounted to 1,100 (± 180) millimeters tion rates were high. Lund et al. (1974), supported later by ‘Fantasia’ nectarine Gilliam et al. (1978), Klein and Bradford orchard at the UC Kearney Research and (1979) and Rees et al. (1995), argued that Extension Center, the nitrate losses in the deep vadose zone experimental site of (due to denitrification) were strongly this study (the orchard correlated with the textural properties was removed in 1998). of the soil. High losses were found in soils with pans or textural discontinui- ties, while losses were limited in relatively homogeneous, well-draining soils in other areas of Southern California. In contrast, Rolston et al. (1996), using isotope analysis at sites in the southern Sacramento Valley and the Salinas Valley, found little evidence of significant denitrification, even in thick unsaturated zones. To study deep unsaturated zone hydrology, we established a research site in a former ‘Fantasia’ nectarine orchard at the UC Kearney Research and Extension Center (KREC) in Fresno County. The objective of our work is to provide a comprehensive assessment of the fate of nitrate in a 52-foot (16-meter) deep alluvial vadose zone that is typical of many agricultural areas in California. The assessment included detailed geologic, hydraulic and geochemical characterization, using nitrate as an example. Field sampling A 12-year fertilizer management experiment (from 1982 to 1995) was implemented in a ‘Fantasia’ nectarine orchard (Johnson et al. 1995). The fertilization experiment consisted of five application treatments in a random block design with triple replicates. Treatments included annual nitrogen application rates ranging from 0 to 325 Fig. 1. In 1997, extensive core drilling was conducted, 2 years after the completion of three pounds per acre (0 to 365 kilograms per orchard nitrate-management trials at KREC with annual fertilizer rates of 0, 100 and 325 hectare [kg/ha])(fig. 1). For the vadose pounds nitrogen per acre. The complete random block design of the management trial and zone characterization, three treatment the three subplots selected for the deep vadose zone drilling are shown. DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 125 Fig. 3. The 10 major lithofacies identified at the two east-west cross sections, 140 and 144 feet from the southern edge of the orchard. The lithofacies, classified in the field according to color, texture and cementation, exhibit vertically varying thicknesses, yet are laterally Fig. 2. Schematic diagram of the Kings River alluvial fan and continuous over the experimental site. Sandy loam is the most fre- its geologic elements. quent textural unit, while clay is the least.

per year (Onsoy et al. 2005). Assuming kilometers) west of the current river KEY (figs. 3, 4): The major lithofacies are: uniform flow conditions throughout channel. The quaternary alluvial sedi- the deep vadose zone at an average ments (that is, sediments deposited by SL1 — recent Hanford sandy loam soil moisture content of 25%, the travel a stream) are derived exclusively from C — clay, very thin Var1 — variable sedimentary structures, time through the deep vadose zone the hard, crystalline Sierran bedrock. predominantly sand was projected to be 3.2 (± 0.5) years. Stratigraphically, the quaternary de- HP1 — shallow paleosol (hardpan), red Based on the leaching rate and travel posits in this part of the valley can Var2 — various textures, sandy loam time, and taking into account that the be divided into five units (Marchand to clay loam experiment ended 1 year prior to drill- and Allwardt 1981): the post-Modesto S — medium sand ing, we estimate that the deep vadose (youngest), Modesto, Riverbank, Upper C-Si-L — clay/clayey silt/clay loam, zone nitrogen storage at the time of and Lower Turlock Lake deposits. fine-textured floodplain deposits drilling would be on the order of 195, Except for the post-Modesto, which is SL2 — sandy loam and 233 and 426 pounds nitrogen per acre less than 10,000 years old (Holocene), HP2 — deep clayey paleosol (hardpan), red in the control, standard and high sub- these deposits are of Pleistocene age plot, respectively. (2 million to 10,000 years old). To confirm this estimate and to de- Most of the stratigraphic units ranges from clay to small gravel and termine the applicability of the uniform (sediment facies) found at the site are includes a wide spectrum of predomi- flow concept, 60 undisturbed sediment believed to represent separate alluvial nantly silty to sandy sediments. The col- cores were obtained in 1997 by drilling episodes related to several Sierran gla- ors of the sediments range from grayish to the water table at a depth of 52 feet ciations. In cores from the study site, brown to yellowish brown, and more (16 meters) using a Geoprobe direct- these deposits appear as intercalated, randomly to strong brown (no signifi- push drilling technique. After geologic thick and thin lenses of clayey silt, silt, cant reduction zones). The thickness of characterization of the complete core sand and gravel from fluvial deposi- individual beds varies from less than sections, 1,200 samples were collected tion. Channel sediments consist of 0.4 inch (1 centimeter) for some finely (approximately one every 2.5 feet [0.8 moderately to well-sorted, subangular layered clayey floodplain deposits to meters]). Samples were collected for to subrounded sand and gravel. These more than 8 feet (2.5 meters) for sandy each sedimentologic stratum or substra- channel deposits are surrounded by streambed deposits. Sharp as well as tum. The soil samples were preserved muddy sand and silts of floodplain gradual vertical transitions are present and stored for later analysis of their deposits (fig. 2)(Page and LeBlanc 1969; between texturally different units. The texture, hydraulic properties (water Huntington 1980; Weissmann et al. relative proportion of the five major tex- content, unsaturated hydraulic conduc- 2002). Deposits from the various periods tural categories found in the sediment tivity and water retention functions) of Sierran glaciations are vertically sepa- cores was 17.2% sand, 47.8% sandy and biochemical properties (pH, dis- rated by paleosols. Paleosols are buried loam, 13.8% silt loam/loam, 8.3% clay solved organic carbon, nitrate-nitrogen, soil horizons that were formed on stable loam/clay and 12.9% paleosol (see side- 15N isotope analysis). upper-fan or terrace surfaces during bars, pages 128 and 129; fig. 4). interglacial periods, when no sediment Geologic framework Hydraulic properties variability deposition took place (fig. 3). The site is located on the Kings River The vadose zone sediments are most Hydraulic properties of the unsatu- alluvial fan, approximately 2 miles (3.2 easily classified by their texture, which rated zone, such as the hydraulic con- DRAFT126 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 Fig. 4. Individual core sections were collected in 4-foot (1.2 meter) plastic tubes (see fig. 1). This image shows all 13 sections of a 52-foot (15.6-meter) core, lined up from the ground surface (upper left) to the bottom of the core (lower right). Missing subsections represent soil sampling locations for hydraulic and chemical analysis.

much hydraulic variability within individual facies as between facies. By far the highest conductivity was observed in sandy facies (“S” and “Var1” in figs. 3 and 4). Heterogeneity of water flow Traditionally, water flow between the root zone (at depths of 6.6 feet ([0 to 2 meters]) and the water table (here a depth of 52.8 feet [16 meters]) has been considered essentially a uniform, vertically downward flow process in a more or less homogeneous vadose zone. Within this conceptual framework, water from individual rainfall or irrigation events is thought to be initially stored in the root zone. There, it is available for uptake by the roots. Surplus water then gradually drains into the deeper vadose zone. Individual rainfall or irrigation events create pulses of moisture that penetrate the root zone profile. Through root water uptake and vertical spreading, the moisture pulse dampens out as it travels downward. In the deeper portions of the ductivity/moisture curve and the water depths at the orchard site. The labora- vadose zone, the downward flow rate retention curve — and the spatial dis- tory tests involved measuring the water has therefore been thought to be equal to tribution of these properties — strongly percolation rates in each core at six to the annual recharge rate. control the flow of water and the trans- 10 different moisture conditions, then However, the highly heterogeneous port of nitrate and other solutes in the determining the hydraulic properties by geology of the alluvial sediments ob- deep vadose zone. (Hydraulic conduc- computer analysis. served at the orchard site, coupled with tivity is a measure of how fast water can Given the large amount of textural the associated heterogeneity of the percolate through the sediments; the variability observed in the cores, it hydraulic properties, suggest that this higher the moisture and the coarser the was not surprising that we found the traditional conceptual framework is sediments, the higher the hydraulic con- hydraulic properties to also vary sig- inadequate to describe how water and ductivity.) Hydraulic properties were nificantly, both with depth and laterally chemicals are transported through the determined in the laboratory on more across the site (Minasny et al. 2003). The vadose zone to the water table. Using than 100 undisturbed sediment core saturated hydraulic conductivity, for our field data and computer simula- samples (3.5 inches [9 centimeters] long example, varied over nearly four orders tion, we reconstructed two-dimensional by 1.5 inches [3.8 centimeters] diam- of magnitude. Within some sedimentary cross-sections of the vadose zone that eter) taken from various locations and layers (facies) we observed nearly as reasonably reflect the spatial variability DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 127 Major facies in the study-site vadose zone

The sand (“S” and “Var1”) is quartz- ish gray in color. The bed thickness rich, and contains feldspar, muscovite, is within a range of a few inches to of the hydraulic properties observed in biotite, hornblende and lithic fragments a foot (centimeters to decimeters). the field, then we simulated water flow consistent with the granitic Sierran Fine-grained sediments often show through this reconstructed vadose zone. source (see figs. 3 and 4). Cross-bedding sharp contacts between the units. Figure 5 illustrates the spatial distribu- at the scale of few inches (centimeters) Changes from one unit to the next ex- tion of the water flux through a hypo- could be observed in some fine-grained ist on small distances. Lamination can thetical cross-section at 40 feet, similar sand samples. The dominant color of more frequently be observed within to that observed at the orchard site. It the sand is a light gray to light brown, silty sediments than in fine sands. captures important features that are char- the brown hue increasing with increas- Root traces and rusty brown–colored acteristic of water flow in heterogeneous ing loam content. The thickness of the mottles are quite common. The depo- vadose zones (Russo et al. 1998; Harter sand beds is as much as 8 feet (2.4 me- sitional environment was presumably and Yeh 1996). Understanding that flow ters), though thickness varies across the the proximal to distal floodplain of occurs in this highly irregular pattern is study site. Very coarse sand and par- the fluvial fan, an area dissected by important for interpreting the field data. ticles up to pebble grain-size (up to 0.4 distributary streams. In particular, figure 5 shows that inch or 1 centimeter) could occasionally The finest sediments are grouped even though the simulated water ap- be observed at the bottom of the sand in the fourth category: silt, clay and plication at the surface was uniform, the units, but were not present in all the clay loam (portions of “C,” “C-Si- heterogeneity of the vadose zone forces cores. The sand units typically show a L” and “Var2”). These are believed water into distinct preferential flow subtle fining-upward succession. The to have been deposited in the distal paths (warm colors), separated by large basal contact is typically sharp. The floodplain and in ponds that devel- areas of relatively stagnant flow (cooler texture and distribution of these sandy oped in abandoned channels. The colors). The preferential flow paths have deposits are consistent with deposition main color is brownish gray to olive highly irregular shapes, but are continu- in a fluvial distributary channel on the brown. Fine, less than 1-millimeter- ous and extend to the water table. The Kings River fluvial fan. One ancient diameter root traces and rusty brown preferential flow paths occupy only a river channel was observed in cores mottles are common in the clay sedi- small portion of the vadose zone. In collected from the orchard site, and it ments. Statistics for the thickness of contrast, areas with relatively stagnant appears to have had a northeast-south- clay layers in the unit between 27 water flow occupy most of the vadose west orientation. The mean thickness and 43 feet (8 and 13 meters) depth zone. Soil moisture differences between of this channel deposit is nearly 6 feet show a mean thickness of 5 inches these two zones are small. Soil moisture (1.7 meters). The basal coarse sand and (12.8 centimeters), but the mode is is therefore not a particularly sensitive pebbles probably represent channel lag about 2.2 inches (3 centimeters). A 20- indicator and may not be useful for deposits that were laid down in deeper inch (50-centimeters) thick clay bed identifying the presence and location of parts of the channels. was observed at approximately 8 feet these preferential flow paths. Sandy loam (“SL1,” “SL2”) is the (2.5 meters) depth in most of the cores. In our study, further field work and most frequent lithofacies within the Paleosols (“HP1,” “HP2”) were computer simulations indicate that the profile. The color is usually light olive recognized in different stages of ma- location of these preferential flow paths to yellowish brown. Some of the sandy turity. They show a brown to strong does not change over time, even though loam sediments are considered to be brown, slightly reddish color, exhibit they may partially or completely dry weakly developed paleosols because aggregates, ferric nodules and con- out between infiltration events. A new of their stronger brownish color, root cretions, few calcareous nodules and event will recreate the same set of pref- traces and presence of aggregates. hard, cemented layers. They also erential flow paths. Mean bed thickness is 20 inches (50 display a sharp upper and a gradual Preferential flow paths are not only centimeters), though individual beds lower boundary as is typical for pa- created by the sediment heterogene- can be as much as 7 feet (2 meters) leosols (Retallack 1990). Clay content ity. Other conditions may also trigger thick. The sorting is moderate to good. decreases downward in the paleosols. and support preferential flow paths: Clay flasers and thin (fractions of an Another feature is fine root traces, macropores in the root zone; flow in- inch, 0.5 to 1 centimeter) clay laminae though these are typically obliter- stability during infiltration into sand or occur in some sandy loam units. Sandy ated in the more mature paleosols. loamy sand soils (Wang et al. 2003); flow loam sediments are assumed to have Paleosols formed in periods of stasis through or above embedded clay or sand developed at the edge of channels, as marked by nonerosion and nonde- lenses (“funneling”)(Kung 1990); and levee or as proximal floodplain depos- position, during the interglacials “fingering” as a result of a sharp textural its near the channels. (Weissmann et al. 2002). The thickness boundary within the vadose zone where Silt loam, loam and silty clay loam of the paleosol horizons ranges from the finer-textured (silt/clay) layer is (portions of “C-Si-L” and “Var2”) are 20 inches (50 centimeters) to about located above a coarse-textured (sand) usually slight olive brown to brown- 7 feet (2 meters). layer (Glass and Yarrington 2003). DRAFT128128 CALIFORNIA CALIFORNIA AGRICULTURE, AGRICULTURE, VOLUME VOLUME 59 ,59 NUMBER, NUMBER 2 2 Study-site geologic profile

A number of distinct sedimentologic units are recognized in the vadose zone profile throughout the orchard and are used to construct a field-scale geologic framework for the research site (see figs. 3 and 4). The deepest parts of the cores (between 50 and 52 feet [15 and 15.8 meters]) display a strong brownish-colored, clay- rich paleosol. This paleosol marks the top of the upper Turlock Lake deposits (Weissmann 2002). Directly above this paleosol, from depths between 40 and 50 feet (12 to 15 meters) below the surface, the Fig. 5. Hypothetical, computer-simulated, unsaturated water flow rates through a heterogeneous vadose zone, illustrating how heterogeneity in the unsaturated zone generates main textural units are sandy loam to fine preferential flow paths: Warmer colors (red, orange, yellow) represent high flow rates, and sandy loam, with some coarse sand and cooler colors (blue, violet, black) represent lower flow rates. The unsaturated hydraulic gravel or fine-grained sediments. In the properties used for the simulation are similar to those found at the KREC research site. cores with fine sediment at the bottom of this unit, a coarsening-upward succession Since much of the annual recharge Agency under the Safe Drinking Water was observed in this zone; in the other occurs through these preferential flow Act. More than half of those occurred cores a fining-upward cycle was observed. paths, the actual downward flow rate in the subplot with the highest nitro- Between 27 and 40 feet (8 and 12 meters) is locally much higher than that esti- gen application. Mean nitrate-nitrogen depth, the sediments are vertically and lat- mated when assuming that the entire concentrations (not including nonde- erally quite heterogeneous with relatively vadose zone uniformly participated in tects) in the control, standard and high thin bedding (thickness of a few inches the downward water flow. Hence, sol- subplot vadose zone were estimated to [centimeters] to a couple of feet [few deci- ute travel times through deep vadose be 5.2, 3.3 and 7.4 mg/L, respectively meters]), consisting mainly of clayey, silty zones are likely shorter than if flow (Onsoy et al. 2005). The nitrate-nitrogen and loamy material. Another strong brown- were indeed uniform. Because of the coefficient of variation (CV) ranged ish paleosol occurs at a depth of 30 to 33 feet shorter travel time, nitrogen storage in from 1.6 to 2.4 within each subplot. The (9 to 10 meters). Between 20 and 30 feet the deep vadose zone should be signifi- difference between the control and stan- (6 and 9 meters) below the surface, a distinct cantly lower than estimated based on dard subplots was statistically not sig- sand layer, representing a former stream the uniform flow concept. On the other nificant due to the large variability. But channel bed, is found. This unit has laterally hand, under heterogeneous conditions, the high subplot yielded significantly varying thickness averaging nearly 6 feet relatively old water may be trapped in larger mean nitrate-nitrogen concentra- (1.7 meters). A weak, mostly eroded paleo- the more stagnant portions of the va- tions throughout the profile, consistent sol was developed on top of the sand unit. dose zone for extended periods. Do the with the overapplication of fertilizer. From about 10 to 13 feet (3 to 4 meters) measured nitrate distribution and water Within all three subplots, slightly to 20 feet (6 meters) below the surface, chemistry in the deep vadose zone at higher nitrate-nitrogen levels were ob- sandy loam with intercalated sand, clayey the Kearney site support this alternative served in the root zone than in the deep and silty material is found. Different trends conceptual framework of water and sol- vadose zone below the root zone, pos- of upward-fining and upward-coarsening ute flow through the vadose zone? sibly due to the last fertilizer application are found on top of each other and laterally in fall 1996, prior to our drilling. Other next to each other within this unit. Nitrogen distribution than that, we observed no significant Immediately above the unit, at a depth To address this question, nitrate- vertical nitrate-nitrogen trend in the of about 10 to 13 feet (3 to 4 meters), a nitrogen (NO3-N) concentrations were deep vadose zone. nearly foot thick (0.2 meter) to more than measured in 809 subsamples of our The highest number of nondetects 10 feet (1 meter) thick paleosol hardpan cores. We found that the data were in- occurred in the coarse-textured, sandy occurs. This paleosol marks the top of the deed highly variable and log-normally lithofacies and in the sand lithofacies Riverbank formation. Recent ground- distributed (the logarithms of the data (above historic water level). There, ap- penetrating radar surveys indicate that were normally distributed). Nitrate- proximately half of the samples had non- this paleosol is laterally extensive across nitrogen concentrations ranged from detectable nitrate-nitrogen levels. This is the orchard site. less than the detection limit of 0.05 mil- consistent with findings that fingering Sandy loam and subordinated loamy ligram per liter (mg/L)(224 samples or preferential flow is particularly domi- sand and loam are present from the top of or 28% of the sample population) to nant in sandy unsaturated sediments. the paleosol to the surface, and represent more than 100 mg/L (two samples). In other words, much of the sand facies the Modesto deposits at the site. About 8 Approximately 10% of the samples does not participate in the flow (stagnant feet (2.5 meters) below the surface, a later- exceeded the maximum contamination moisture) and would see little or none ally continuous clay horizon with a thick- level for drinking water (10 mg/L), set of the nitrate-nitrogen that is passing ness of few inches (centimeters) is found by the U.S. Environmental Protection through the preferential flow paths. in most of the cores. DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL-JUNEAPRIL–JUNE 20052005 129129 Most importantly, the total nitrogen mass estimated directly from the measured nitrate-nitrogen distribution in the deep vadose zone was only 46 (± 9), 37 (± 6) and 83 (± 12) pounds per acre annually for the control, standard and high subplots, respectively. This is less than one-quarter of the total nitrogen mass in the deep vadose zone that was indirectly estimated from the mass balance described above, which is based on the conventional uniform flow concept. Role of denitrification Traditionally, such low nitrate-nitro- Fig. 6. Composite nitrate-nitrogen, dissolved organic carbon (DOC) and δ15N profiles from gen mass in the deep vadose zone has borings at the orchard study site. Higher DOC indicates a higher potential for denitrification. been attributed to denitrification (the Higher δ15N levels (above 10) indicate the occurrence of partial denitrification. microbial breakdown process of nitrate by soil microbes). However, the lack of a significant vertical trend in the aver- of −5‰ to 5‰ (Rolston et al. 1996). transport in heterogeneous soils as well age nitrate-nitrogen concentration does Denitrification decreases nitrate- as that predicted by numerical models not support that hypothesis (denitrifi- nitrogen concentrations, but increases of flow and transport in highly hetero- cation in the deep vadose zone would the relative amount of isotopically geneous vadose zones (Harter and Yeh 15 create a nitrate-nitrogen profile that heavy NO3− δ N. Indeed, there was a 1996). Hence, the proposed conceptual shows decreasing concentration with very weak trend (R2 < 0.1) to support framework of preferential flow in the depth). To further evaluate whether the hypothesis that a limited amount of deep vadose zone may provide the denitrification played a significant role denitrification may occur in the vadose answer: preferential flow paths, which in the deep vadose zone, we measured zone: samples with 2 mg/L to 10 mg/L are responsible for most of the water the amount of soluble organic carbon nitrate-nitrogen had relative δ15N lev- and solute transport from the root zone (a microbial food source) and the els of 5‰ to 12‰, while samples with to the water table, quickly flushed amount of δ15N (a rare nitrogen isotope higher nitrate-nitrogen contained from nitrate-nitrogen to deeper portions of that increases in relative abundance 0‰ to 6‰ of δ15N. (No δ15N measure- the vadose zone and to the water table, when denitrification occurs) in the ments could be made on samples with allowing for little or no denitrification. nitrate-nitrogen of samples from four less than 2 mg/L nitrate-nitrogen.) This would explain the occurrence of cores (three from the high subplot and There was significant scatter in high nitrate-nitrogen levels and low one from the standard subplot). (The these data, corroborating the concept δ15N levels throughout the depth of the concentration of isotopes is not report- of highly heterogeneous transport. vadose zone profile. ed in absolute values, but rather as a Furthermore, just as there was no sig- Lower nitrate-nitrogen would occur relative concentration, hence the nota- nificant decrease in nitrate-nitrogen in stagnant water zones outside pref- tion “delta” or “δ” 15N. A value of δ15N with depth, there was no significant erential flow paths. Due to their longer = 5‰ indicates that the 15N concentra- increase in δ15N with depth, similar to residence time, nitrate-nitrogen in these tion is 5 permil above normal [1 permil isotopic results at geologically similar zones was apparently subject to a small = 0.1 percent].) Yolo County and Salinas Valley sites amount of denitrification, which would Soluble carbon was found to be very (Rolston et al. 1996). Then why was the explain the higher levels of δ15N that low, not favoring high rates of microbial total nitrogen storage in the deep va- were also found, scattered throughout degradation anywhere in the vadose dose zone so low? most of the profile. zone profile. The δ15N values varied The nitrate distribution pattern The importance of this finding is from 0‰ to 12‰ and averaged 6‰ that we found (fig. 7) was similar to that while limited denitrification took (fig. 6). Without denitrification, δ15N that postulated in other experimental place in the stagnant water areas of levels are expected to be in the range studies specifically designed to assess the vadose zone, the majority of the DRAFT130 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 Fig. 7. Measured core nitrate-nitrogen data (squares) and three-dimensional, kriged (yellow) contours of nitrate-nitrogen data. The

kriged isosurfaces (only for NO3-N > 1 mg/L) are obtained from geostatistical analyses of the water content and nitrate measurements at the sampling locations. The standard subplot yielded the largest areas of negligible

nitrate concentrations (NO3-N < 1 mg/L) among the three subplots. High concentrations are seen in the upper proﬁle and near the water table.

nitrate-nitrogen transport occurred in preferential flow paths, where no significant denitrification appears to have taken place. Hence, the low average nitrate-nitrogen concentration in the vadose zone pore water should not be interpreted as an indicator for high denitrification and low nitrate impact on groundwater. Rather, it may be the result of swift, unattenuated nitrate- nitrogen transport to the water table deep vadose zone below the root zone water and is not effectively represented (the same may apply to the root zone). may be subject to significant preferential by composite soil samples. It appears that flow patterns with significantly faster the average or composite nitrate-nitrogen Analysis shows variability travel times than would be estimated concentrations are also not appropriate Our detailed geologic, hydraulic and under uniform flow assumptions. for estimating the amount of denitrifica- geochemical analysis of a typical deep Faster travel times not only decrease tion as a closure term to the nitrogen mass vadose zone in the eastern San Joaquin the potential for denitrification, but also balance. We are currently implementing Valley demonstrated that alluvial va- decrease the potential for natural at- detailed heterogeneous flow and trans- dose zones are subject to significant geo- tenuation of pesticides. port simulations to further support these logic variability, which in turn causes Our work suggests that the traditional findings and to develop guidelines for the hydraulic properties and water flow interpretation of deep vadose zone mea- sampling the deep vadose zone. in the vadose zone to exhibit strong surements should be reconsidered. The spatial variability. While such variability assumption of uniform flow is not appli- is expressed to only a limited degree in cable to many alluvial vadose zone sites. the variability of the observed moisture The common practice of compositing soil T. Harter is Associate Groundwater Quality content, it leads to highly variable con- samples taken from immediately below Hydrologist (UC Cooperative Extension), centrations of chemicals, such as nitrate. the root zone provides an estimate of the Department of Land, Air and Water Re- Our research presents new evidence average nitrate-nitrogen concentration sources, UC Davis; Y.S. Onsoy is consul- indicating that unsaturated water flow at that depth. However, our work indi- tant and Doctoral Candidate, UC Davis; and transport of nitrate and other agro- cates that recharge water may constitute K. Heeren is freelance geologist in environ- chemicals (such as pesticides) in the only a minor portion of that vadose zone mental education, Germany; M. Denton is DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 131 Before it is pumped to the surface for agricultural or other uses, groundwater per- colates through the geologically variable vadose zone. Based on this study, current assumptions about transport of nitrate from fertilizers and other agricultural chemicals need to be reexamined.

2003. Neural networks prediction of soil consultant and obtained a master’s degree References hydraulic functions from multi-step outflow in hydrologic studies, Department of Gilliam JW, Dasberg S, Lund LJ, Focht DD. data. Soil Sci Soc Amer 68:417–29. Land, Air and Water Resources, UC Da- 1978. Denitrification in four California soils: Onsoy YS, Harter T, Ginn T, Horwath WR. vis; G. Weissmann is Assistant Professor Effect of soil profile characteristics. Soil Sci 2005. Spatial variability and transport of Soc Amer 42:61–6. nitrate in a deep alluvial unsaturated zone. of Hydrogeology, Department of Geologi- Glass RJ, Yarrington L. 2003. Mechanistic Vadose Zone J 4(1):41–54. cal Sciences, Michigan State University; modeling of fingering, nonmonotonicity, Page RW, LeBlanc RA. 1969. Geology, hy- and J.W. Hopmans is Professor of Vadose fragmentation, and pulsation within grav- drology and water quality in the Fresno area, ity/buoyant destabilized two-phase/unsatu- California. USGS Open-File Rep. 70 p. Zone Hydrology, and W.R. Horwath is rated flow. Water Resour Res 39(3):1058, Pratt PF, Jones WW, Hunsaker VE. 1972. Associate Professor of Soil Biogeochemis- DOI:10.1029/2002WR001542. Nitrate in deep soil profiles in relation to try, Department of Land, Air and Water Harter T, Yeh T-CJ. 1996. Stochastic analy- fertilizer rates and leaching volume. Environ Resources, UC Davis. sis of solute transport in heterogeneous, Qual 1:97–102. variably saturated soils. Water Resour Res Rees TF, Bright DJ, Fay RG, et al. 1995. The California Fertilizer Research and 32(6):1585–95. Geohydrology, water quality, and nitrogen Education Program, California Tree Fruit Huntington GL. 1980. Soil-land form rela- geochemistry in the saturated and unsatu- Agreement, UC Water Resources Center, tionships of portions of the San Joaquin River rated zones beneath various land uses, River- Geoprobe Systems and Studienstiftung and Kings River alluvial depositional systems side and San Bernardino Counties, California, in the Great Valley of California. Ph.D. disser- 1991–93. USGS Water Resour Invest Rep des Deutschen Volkes provided support for tation, UC Davis. 147 p. 94–4127. 267 p. this project. We would like to thank Kevin Johnson RS, Mitchell FG, Crisosto CH. Retallack GJ. 1990. Soils of the Past — An Pope, formerly with Geoprobe Systems, Jean 1995. Nitrogen fertilization of Fantasia nec- Introduction to Paleopedology. Hyman U tarine: A 12-year study. UC Kearney Tree Fruit (ed.). Winchester, MA. 520 p. Chevalier with his crew at KREC, and Dick Rev 1:14–9. Rolston D, Fogg GE, Decker DL, et al. Rice and R. Scott Johnson at the UC Kear- Klein JM, Bradford WL. 1979. Distribution 1996. Nitrogen isotope ratios identify nitrate ney Agricultural Center for their support of nitrate and related nitrogen species in the contamination sources. Cal Ag 50(2):32–6. during the field work; Anthony Cole, Chad unsaturated zone, Redlands and vicinity, San Russo D, Zaidel J, Laufer A. 1998. Nu- Bernardino County, California. USGS Water merical analysis of flow and transport in a Pyatt and Rigo Rios for drilling the 3,000 Resourc Invest Rep 79–60. 81 p. three-dimensional partially saturated hetero- feet of vadose zone cores at the site; Andrea Kung K-JS. 1990. Preferential flow in a geneous soil. Water Resour Res 34(6):1451–6. DeLisle and Timothy Doane for their ana- sandy vadose zone: 1. Field observations. Wang Z, Wu L, Harter T, et al. 2003. A Geoderma 46:51–8. field study of unstable preferential flow dur- lytical chemistry work; Jim MacIntyre for Lund LJ, Adriano DC, Pratt PF. 1974. Ni- ing soil water redistribution. Water Resour implementation of the multistep outflow trate concentrations in deep soil cores as Res 39(4), 10.1029/2001WR000903, 01 April experiments needed to determine the hy- related to soil profile characteristics. Environ 2003. draulic properties at the site; and Atac Tuli Qual 3:78–82. Weissmann GS, Mount JF, Fogg GE. 2002. Marchand DE, Allwardt A. 1981. Late Ce- Glacially-driven cycles in accumulation space for his support in developing the necessary nozoic stratigraphic units, northeastern San and sequence stratigraphy of a stream- software to use in conjunction with the mul- Joaquin Valley, California. USGS Bull 1470. dominated alluvial fan, San Joaquin Valley, tistep outflow experiments. Minasny B, Hopmans JW, Harter T, et al. California. J Sediment Res 72:270–81. DRAFT132 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 REVIEW ARTICLE ▼ Weighing lysimeters aid study of water relations in tree and vine crops

R. Scott Johnson Larry E. Williams James E. Ayars Tom J. Trout Jack Kelly Clark ▼

In 1986, two large weighing lysimeters, — one in a peach orchard and the other in a grape vineyard — were constructed at the UC Kearney Research and Extension Center as a Since a lysimeter is the most joint effort between UC and the U.S. precise technique for measuring Department of Agriculture’s Water crop evapotranspiration, its Management Laboratory. Hourly weight changes in the lysimeters measurements can be compared have been used to measure the daily with those of other less-expensive and seasonal water use of trees and methods for validation. vines for nearly 20 years. Peaches and grapes exhibit similar seasonal crop-coefficient patterns that start as UC pomology specialist R. Scott Johnson, above, adjusts the balance beam in one of two low as 0.1 in March, increase linearly lysimeters constructed at the UC Kearney Research and Extension Center. These rare research until early July and then remain tools are large and expensive to maintain, which is why so few of them exist around the world. For 20 years they have been the most precise method of understanding daily and constant between 1.1 and 1.2 for the seasonal water use in the San Joaquin Valley. Every hour soil evaporation and plant transpi- remainder of the season (provided ration — crop “evapotranspiration” — is recorded. When a threshold value is exceeded, the trees or vines growing in the lysimeters are automatically irrigated. the plants remain disease-, pest- and stress-free). The linear increase A weighing lysimeter is simply a large joint effort between UC and the U.S. phase is proportional to the increase “flower pot” resting on a sensitive, un- Department of Agriculture’s Water in canopy light-interception and derground scale. Short-term weight loss Management Laboratory. Each lysimeter leaf area. These relationships have from the system is almost entirely due consists of an underground chamber facilitated modeling to predict crop to water transpired through leaves or that houses a balance-beam weighing evapotranspiration under various evaporated from the soil surface. system constructed by Fred Lourence conditions. The peach lysimeter has While this technique is generally con- (Precision Lysimeters, Red Bluff, Calif.) also been useful for studying the sidered one of the most reliable because upon which rests a rectangular box it is simple and direct (Aboukhaled et al. measuring 6.5 feet wide by 13 feet long effects of water stress on tree water 1981), weighing lysimeters are expensive by 6.5 feet deep (Phene et al. 1991; use and for evaluating other methods to install and maintain, so relatively few Williams et al. 2003b). In constructing of estimating water use. have been constructed around the world, the underground chamber, soil was re- especially to study perennial trees and moved in 6-inch increments so it could ater is a critical resource in agri- vines. At the UC Kearney Research and be replaced in the box at approximately culture, and supplying the right Extension Center (KREC), we have had the same depth as the surrounding soil. amountW is essential for healthy plants two of these instruments for nearly 20 In spring 1987, two peach trees were and optimum productivity. With insuffi- years. They have been particularly useful planted in one lysimeter and two grape cient water, plants become stressed and for determining patterns of tree and vine vines were planted in the other, and in unproductive, and eventually die. With crop coefficients, studying water-stress each case the surrounding 3 acres were an excess, they can suffer from diseases, effects on water use, and evaluating oth- planted to the same variety and spac- nutritional disorders and waterlogged er techniques for estimating water use. ing. The grape variety was ‘Thompson soils. The most accurate way to estimate Seedless’ (clone 2A) with 7-feet-by-11.5- Lysimeter and field design water use by crops is with a weighing feet spacing. The peach variety was lysimeter, which measures water loss In 1986, two large weighing lysim- initially ‘O’Henry’ (late-July harvest) from the plants and surrounding soil. eters were constructed at KREC as a on ‘Nemaguard’ rootstock, with 6-feet- DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 133 Fig. 1. Hourly crop evapotranspiration (ET) on June 9, 1996, as mea- Fig. 2. Seasonal pattern of crop coefficients sured by the Kearney grape and peach lysimeters. Reference ETo for mature grapevines (1996) and peach was obtained from a nearby CIMIS weather station. trees (average from 2001 to 2003) as calculated from lysimeters. Each data point is a weekly average. Regression lines are by-16-feet spacing. In 1997, the mature The lysimeters have been in con- for data collected from bud-break through early July (about day 180). ‘O’Henry’ trees were removed from the tinuous operation since 1987. Every lysimeter and surrounding orchard and hour, the lysimeter boxes (including replaced in 1999 with ‘Crimson Lady’ soil, plants and suspended irrigation (late-May harvest) peaches, which were tanks) are automatically weighed to irrigation efficiency, the amount of wa- also on ‘Nemaguard’ rootstock at the determine water loss, which includes ter to apply can be determined. same spacing. both soil evaporation and plant tran- Tree and vine crop coefficients Each lysimeter has two separate spiration and is often referred to as

irrigation systems, one below and “crop evapotranspiration,” or ETc. The During normal midsummer days in the other above the ground. The un- values are recorded with a data logger central California, with hot tempera- derground irrigation systems are 12 (Campbell Scientific Instruments, 21 tures and cloudless skies, the lysim- inches and 24 inches deep in the peach XL Micrologger, Logan, Utah) and the eters generate smooth daily ETc graphs lysimeter, and 16 inches deep in the mass change is compared to a thresh- with minimal noise (fig. 1). During grape lysimeter. Each underground old value. When this value is exceeded, periods of unsettled weather, the ly- system has 1-gallon-per-hour (gal/hr) the trees or vines are automatically simeter output is more variable from emitters every 12 inches on either side irrigated. Generally, low threshold one hour to the next, but has generally of the plants. The aboveground irriga- values have been used so that multiple followed the same pattern as ETo , re- tion systems consist of a single in-row irrigations per day are called for in the sulting in consistent day-to-day crop- line on or above the soil surface. The summer. This maintains soil moisture coefficient values. grape lysimeter’s system is suspended content close to field capacity and The typical seasonal crop-coefficient 16 inches aboveground and has 1 gal/ minimizes any water stress effects. At pattern of mature plants for both peaches hr in-line drip emitters every 12 inches. midnight each day, the water tanks are and grapes starts as low as 0.1 to 0.2 The peach lysimeter’s aboveground automatically refilled to a preset level, early in the spring and increases steadily system had a 3.5-foot-diameter and the new lysimeter mass is set as until early July (fig. 2)(Ayars et al. 2003; circle of ten 0.5 gal/hr drip emitters the baseline for the next day. Williams et al. 2003a). Grape is delayed every 12 inches around each tree Hourly reference crop evapotran- somewhat compared to peach because it

when planted with ‘O’Henry’, and spiration (ETo) values are calculated is more severely pruned and takes longer a single 26 gal/hr emitter that fills by a modiﬁed Penman equation us- to develop its canopy. For the remainder a 4-foot diameter basin around each ing weather data collected from a of the season, the crop coefﬁcients for tree when planted with ‘Crimson nearby CIMIS (California Irrigation both crops leveled off at values between Lady’. Irrigation water is supplied Management Information System) 1.1 and 1.2. The seasonal pattern of young by two 80-gallon polyethylene tanks weather station. This equation was de- trees and vines has also been determined suspended from and included in the veloped by scientists to estimate grass (Johnson et al. 2002; Williams et al. 2003b). total mass of the lysimeters. ET and is used as a standard around The Kearney lysimeter research has

In addition, the lysimeters can the world. Daily summed ETc values elucidated factors affecting the water use control the low-volume irrigation sys- are divided by daily summed ETo to of trees and vines, allowing for the bet- tems in the surrounding fields. The provide a crop coefficient (Kc) for each ter estimation of crop coefficients under vineyard is irrigated by a single line day. Once a seasonal pattern of crop conditions different from those in the ly- of drip tubing suspended 16 inches coefficients has been established, this simeter fields. One factor that has clearly above the soil with 1 gal/hr in-line information can be used to guide ir- been demonstrated is between canopy emitters every 12 inches. Each tree rigation amounts. The crop coefficient light interception and tree water use

in the peach orchard has a 6.7 gal/hr multiplied by ETo for a given time pe- (Johnson et al. 2000), or leaf area and vine spray emitter with about a 10-foot riod gives an ETc value for that same water use (Williams et al. 2003a). This radius. period of time. Then, after adjusting for relationship holds true for both young DRAFT134 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 Left and center, construction of the two large weighing lysimeters at KREC began that crop coefficients decrease toward in 1986. Each lysimeter consists of an un- Water stress and water use derground chamber that houses a balance- the end of the growing season (Williams beam weighing system with a rectangular et al. 2003a), these decreases were due The lysimeters have also been useful “flower pot” measuring 6.5 feet wide by 13 feet long by 6.5 feet deep. Right, researchers to insect pest defoliation (Daane and for evaluating how water stress affects enter the completed lysimeter. Williams 2003) or irrigation cutoff various parameters, particularly water (Ayars et al. 2003). Such late-season use. In 1996, the peach lysimeter was declines in crop coefficients were not subjected to a 3-week drying cycle and observed in either lysimeter as long during that time frequent measure- as the plants were kept healthy, free of ments were made of soil water content, and mature trees and vines. The steadily pests and well watered. Therefore, even predawn leaf water-potential and mid- increasing crop coefficients throughout though there may be horticultural or day stem water-potential (Mata et al. the spring (fig. 2) are primarily due to the pest management reasons for cutting 1999). Water potential is measured with tree or vine’s expanding canopy and its back irrigation water at the end of the a pressure chamber and basically indi- increasing interception of light. season, there does not appear to be a cates the tension of water in the leaf. All The Kearney peach lysimeter yielded physiological basis for it. The Kearney three parameters showed strong correla- a crop-coefficient pattern (Ayars et al. lysimeter research has clearly demon- tions with tree water use. 2003) distinctly different from previously strated that as long as they are kept For soil water content, tree water published values for deciduous fruit healthy, peach trees and grapevines are use started to decline when the avail- crops (Snyder et al. 1989). The published capable of using significant amounts of able water content decreased by 20% values, which were derived primarily water throughout the growing season. in the top 33 inches of soil, and then from almond trees, start at about 0.5 in However, it is important to em- declined steadily as the water content the spring and increase to peak values of phasize that the lysimeters measure continued to decrease. For predawn less than 1.0. Thus, the lysimeter-derived water use under conditions of high leaf water-potential and midday stem peach crop-coefficient pattern starts soil-water availability, which are not water-potential there was a continual much lower initially in the spring, but by necessarily the best conditions for decline in water use across all values, midsummer reaches a higher plateau. optimum production, tree health and suggesting that either measurement These differences can be attributed to fruit quality. A study in the grape ly- could be useful in determining how differences in the canopy development simeter vineyard showed that yields well irrigation is supplying full crop

of peach and almond trees. Almonds are were maximized when moderate ETc and in assessing tree water stress. minimally pruned and quickly develop a water stress was imposed by limiting Similar relationships have also been spur canopy (many short shoots), which water applications throughout the found for grapevines (Williams and has high light-interception in the spring. season to between 60% and 80% of Araujo 2002).

In contrast, peach trees are more heav- lysimeter water use (full ETc)(Williams A second study of more moderate ily pruned and require extensive shoot 2000). Likewise, there are many fruit- water stress was conducted in the peach growth before they develop a full canopy. tree studies showing the benefits of lysimeter in 2002. Three short-term These differences indicate that separate imposing moderate water stress at drying cycles of about 1 week were im- crop-coefficient values may be needed for different periods of the growing sea- posed during 3-week periods in early different deciduous fruit-tree species and son. Ongoing research is needed to June and again in late July. During each grapevines, depending on pruning and develop deficit-irrigation (less than cycle, daily measurements were made

canopy development parameters. full ETc) management strategies that of midday stem water-potential. As in The maximum midsummer crop- optimize fruit quality, plant health the 1996 study, there was a linear de- coefﬁcient values of 1.1 to 1.2 are greater and long-term productivity. To aid cline in tree water use with decreasing than those reported in the past for trees in irrigation management, a model midday stem water-potential values and vines. However, these values are to predict peach-tree water use has (ﬁg. 3). Absolute water use was higher not out of line with recent reports on been developed using lysimeters to in late July than early June because of a wide range of crop plants including quantify the relationships among light greater leaf area. However, the slope of beans, corn, cotton, sugar cane and pis- interception, soil evaporation, tree di- the relationship was similar for both of tachios (Allen et al. 1998). In addition, mensions and tree water use (Johnson these periods as well as during the 1996 while other researchers have reported et al. 2002, 2004). study, which suggests midday stem DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 135 Larry Williams

Fig. 3. Relationship between peach tree crop-coefﬁcient (Kc = ETc/ETo) and midday stem water-potential (MSWP) for two periods of three dry-down cycles (no irrigation for 5 to 7 days) in 2002. MSWP is expressed in units of mega-pascals (MPa), a measure of water tension in the plant.

water-potential might be a consistent and Extension Center; and J.E. Ayars tool for irrigation management in peach and T.J. Trout are Agricultural Engi- trees. Indeed, this measurement has neers, U.S. Department of Agriculture, The Kearney lysimeters have been in con- proven to be useful both for predicting Agricultural Research Service, San Joa- stant use since 1987. One lysimeter measures water stress and for helping schedule ir- quin Valley Agricultural Sciences Cen- water use in peaches, top, the other ‘Thomp- son Seedless’ grapes, bottom. The lysimeters rigation for a range of tree and nut spe- ter, Parlier. The authors express sincere have provided more accurate evapotrans- cies in California (Shackel et al. 1997). appreciation for the technical assistance piration values for peach trees and grape of Pete Biscay, David Clark, Dale Hand- vines, information necessary in irrigation Methods for estimating water use ley, Glenn Hoffman, Kevin Klassen, management decisions that ultimately affect plant health and fruit quality. Since a lysimeter is the most precise Richard Mead, Becky Phene, Claude

technique for measuring ETc , its output Phene, Richard Soppe and Paul Wiley. can be compared with that of other References less expensive methods for valida- the tree evaluated as stem water potential and Aboukhaled A, Alfara A, Smith M. 1981. crop water stress index. M.S. thesis. California tion. The peach lysimeter has shown Lysimeters. FAO Irrigation and Drainage Pa- State University, Fresno. 98 p. that two such methods are inaccurate per No 39. FAO, Rome. Phene C, Hoffman GJ, Howell TA, et al. but that others may be promising. The Allen RA, Pereira LS, Ross D, Smith M. 1991. Automated lysimeter for irrigation and two inaccurate methods are the heat 1998. Crop evapotranspiration: Guidelines drainage control. In: Lysimeters for Evapotrans- for computing crop water requirements. FAO piration and Environmental Measurements. IR balance technique for estimating sap Irrigation and Drainage Paper No 56. FAO, Div/ASCE, Honolulu, HI. p 28–36. flow (Shackel et al. 1992) and the use of Rome. Shackel KA, Ahmadi H, Biasi W, et al. 1997. leaf-to-air temperature differences, as Ayars JE, Johnson RS, Phene CJ, et al. Plant water status as an index of irrigation measured by an infrared sensor to esti- 2003. Water use by drip-irrigated late-season need in deciduous fruit trees. Hort Technol peaches. Irrig Sci 22:187–94. 7(1):23–9. mate stress (Medawar 1991). Promising Daane KM, Williams LE. 2003. Manipulat- Shackel KA, Johnson RS, Medawar CK, methods, such as the measurement of ing vineyard amounts to reduce insect pest Phene CJ. 1992. Substantial errors in estimates stem water-potential mentioned above, damage. Ecol Applic 13:1650–66. of sap flow using the heat balance technique Fereres E, Goldhamer D, Cohen M, et al. on woody stems under field conditions. J Amer also include the continuous monitoring 1999. Continuous trunk diameter recording Soc Hort Sci 117(2):351–6. of diurnal changes in trunk diameter can reveal water stress in peach trees. Cal Ag Snyder RL, Lanini BJ, Shaw DA, Pruitt WO.

(shrinking and swelling) as an irrigation 53(4):21–5. 1989. Using reference evapotranspiration (ETo) guide (Fereres et al. 1999; Goldhamer Goldhamer DA, Fereres E, Salinas M. and crop coefficients to estimate crop evapo- 2003. Can almond trees directly dictate their transpiration (ETc) for trees and vines. UC Co- et al. 2003). As more techniques for es- irrigation needs? Cal Ag 57(4):138–44. operative Extension. DANR Leaflet 21428. 8 p. timating water use are developed, such Johnson RS, Ayars J, Hsiao T. 2002. Model- Williams LE. 2000. Grapevine water rela- as those involving remote sensing or de- ing young peach tree evapotranspiration. tions. In: Christensen LP (ed.). Raisin Produc- Acta Hort 584:107–13. tion Manual. UC DANR Pub 3393. Oakland, CA. tailed meteorological data, the Kearney Johnson RS, Ayars J, Hsiao T. 2004. Im- p 121–6. lysimeters will be valuable instruments proving a model for predicting peach tree Williams LE, Araujo F. 2002. Correlations for validation purposes. evapotranspiration. Acta Hort 664:341–6. among predawn leaf, midday leaf and midday Johnson RS, Ayars J, Trout T, et al. 2000. stem water potential and their correlations Crop coefficients for mature peach trees are with other measures of soil and plant water well correlated with midday canopy light in- status in Vitis vinifera L. J Amer Soc Hort Sci terception. Acta Hort 537:455–60. 127:448–54. R.S. Johnson is Pomology Specialist, Mata M, Girona J, Goldhamer D, et al. Williams LE, Phene CJ, Grimes DW, Trout TJ. Department of Plant Sciences, and L.E. 1999. Water relations of lysimeter-grown 2003a. Water use of mature Thompson Seed- peach trees are sensitive to deficit irrigation. less grapevines in California. Irrig Sci 22:11–8. Williams is Professor, Department of Cal Ag 53(4):17–21. Williams LE, Phene CJ, Grimes DW, Trout TJ. Viticulture and Enology, UC Davis, both Medawar C. 1991. Size and growth of 2003b. Water use of young Thompson Seedless stationed at the UC Kearney Research O’Henry peaches related to water status of grapevines in California. Irrig Sci 22:1–9. DRAFT136 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 RESEARCH ARTICLE ▼ Ozone reduces crop yields and alters competition with weeds such as yellow nutsedge

David A. Grantz Anil Shrestha ▼

In recent decades, air quality has Photos: Jack Kelly Clark improved near most cities but not in rural areas such as the San Joaquin Valley. Many studies using diverse exposure techniques have shown that ground-level ozone air pollution reduces plant growth and yield, from negligible impacts in some species to over 30% losses in others. We studied the interaction of ozone with weed competition from yellow nutsedge in Pima cotton and tomato in open- top field-exposure chambers at the UC Kearney Research and Extension Center in Fresno County. Ozone impacts on cotton (which is relatively sensitive) were compounded by weed Open-top chambers at KREC, used to expose crops and weeds competition, whereas tomato (which to realistic daily time courses of ozone. is less sensitive) competed well at all ozone concentrations. Our data suggests that crop-loss estimates obtained in single-factor experiments accurately reflect the serious risk of ozone to agriculture, but that more accurate yield predictions will require the consideration of interactions between the components of complex crop production systems, including weed competition. Top, Kearney-based air pollution effects specialist David Grantz (right) and technician Margo Toyota (left) evaluate ozone impacts on cotton in an open-top chamber (OTC) at Kearney. At current ozone concentrations in the San Joaquin Valley, yields can decline up he economic viability of crop pro- to one third depending on the crop. Bottom, Grantz checks cotton plants growing in a duction in the San Joaquin Valley closed chamber in Kearney’s new state-of-the-art greenhouse. isT threatened in many ways. Chronic threats include reduced crop vigor “good,” in that it absorbs ultraviolet stone, paint and plastics. This ground- caused by competition from newly light, protecting against sunburn, skin level ozone, or smog, inhibits lung de- introduced weeds, some of which are cancer and damage to vegetation and velopment in children, induces asthma increasingly difficult to control, and sensitive aquatic species. attacks and has been linked to increased damage caused by the changing global In contrast, ozone produced at hospital admissions and deaths. climate, including increased ground- ground level and mixed into the air, up Ground-level ozone is derived from level ozone (Fuhrer 2003). Ozone can to about 6 to 12 miles (10 to 20 kilome- emissions of oxides of nitrogen (from be either “good” or “bad,” depending ters; the troposphere), is mostly attribut- high-temperature combustion includ- on where it is in the atmosphere. Ozone able to human activity and is considered ing automobiles, power plants and in the upper atmosphere between 10 “bad.” It is a strong oxidant in the envi- factory boilers) and emissions of vola- to 30 miles (15 to 50 kilometers; the ronment, injuring human lungs, crops tile organic compounds (evaporating stratosphere) is naturally occurring and and native plants, and materials such as gasoline, paints and solvents, pesticides DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 137 TABLE 1. Estimated statewide crop loss (%) in California caused by ground-level ozone, 1993

Crop Yield loss* % Annual Lettuce 0.5 Fresh-market tomato 0.6 Field corn 1.2 Rice 3.9 Wheat 6.7 Processing tomato 6.8 Onion 10.6 Dry bean 17.5 Upland cotton† 23.3 Cantaloupe 32.8 Perennial Lemon 8.4 Alfalfa 9.5 Orange 14.0 Wine grape 22.8 Raisin grape 26.2 Table grape 29.9 Fig. 1. Trends of ozone air quality in the (A) Los Angeles and (B) San * Statewide yield-loss data from Mutters and Soret (1998), using 7-hour (27.2 ppb) and 12-hour (25 ppb) Joaquin Valley air basins. The high concentrations observed in the mean ozone exposure crop-loss models. Losses are 1970s in the Los Angeles air basin are no longer observed; the San relative to clean background air. Joaquin Valley and Los Angeles basins recently traded places as † Data is for upland cotton; comparable data for Pima having the worst air in the United States. cotton is not available.

and plant products including fragrant of the older federal air-quality standard) emissions in the United States, about compounds). Natural background con- and for the newly established 8-hour 60% of all ozone (1993 data from U.S. centrations of ground-level ozone are average (the basis of the newer federal Environmental Protection Agency, about 20 to 25 parts per billion by vol- standard). However, neither region meets www.epa.gov/ebtpages/air.html), and ume (ppb). As concentrations increase either standard. The San Joaquin Valley only eight major crops, the estimated above this level they become increas- and Los Angeles air basins seem to be economic damage due to ambient ozone ingly harmful to human health. The trading places as the most polluted re- in 1990 ranged from $2.8 billion to $5.8 California health-based 1-hour standard gions in the United States. billion (Murphy et al. 1999). is 90 ppb (fig.1A) and the federal stan- San Joaquin Valley crops are grown in Despite its “big city” ozone prob- dard is 120 ppb (fig.1B), although both increasingly agroecological systems, with lem, the San Joaquin Valley remains standards may be too high to be protec- emphasis on integrated pest management. the dominant agricultural area of tive. Crops are damaged above concen- A critical component of these systems is California. An economic cost-benefit trations of 40 to 60 ppb. crop competition with other vegetation. analysis (Kim et al. 1998) suggested that Ground-level ozone is a long-standing Weeds cause considerable crop loss despite controlling peak ozone concentrations and worsening problem in many rural the extensive use of control technologies. to 150 ppb in Tulare, Kings, Fresno and areas. Curiously, while rural air quality However, weed management in the San Madera counties would provide substan- has not improved rapidly, air quality in Joaquin Valley may be further threatened tial economic benefits, even though Los Angeles and other major metropoli- by restrictions on herbicide use, due in part 150 ppb is well above the threshold (40 tan areas has. This difference is due to to air-quality concerns, and by the estab- to 60 ppb) for crop damage, and peaks rapid population growth in affordable lishment of herbicide-resistant weeds. above 150 ppb occur infrequently in the rural areas such as the Central Valley, and Valley (California Air Resources Board, Ozone and crop loss the initial abundance in urban areas of www.arb.ca.gov/aqd/aqdpage.htm). easily identifiable air pollution sources Current ambient ozone concentra- Current ambient ozone concentrations such as factories and industrial processes. tions impose substantial economic in the San Joaquin Valley can cause yield The steep decline in ozone concentra- costs on producers and consumers of losses from nearly none to as much as a tions at the Rubidoux monitoring site agricultural products in the United third, depending on the crop (Mutters in Riverside County, in the South Coast States (Spash 1997). Considering only and Soret 1998). Crop species, and even (Los Angeles) air basin, contrasts dra- ozone derived from motor vehicle cultivars within a species, differ in both matically with the nearly flat trend at the Parlier monitoring site at the UC Kearney Ozone now causes economically significant losses in the Research and Extension Center (KREC) yields of most crops, and this will get worse if current in the San Joaquin Valley air basin (fig. 1). Similar trends are observed for the 1-hour trends in rural population density continue. average ozone concentration (the basis DRAFT138 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 Photos: California Air Resources Board

Los Angeles used to be the most polluted air basin in the United States. Left, a smoggy day in the city’s downtown; right, a clear day.

sensitivity to ozone and in the ambient methods are available (Heagle et al. a threshold concentration (60 ppb or ozone environments in which they are 1988; Olszyk et al. 1986). 40 ppb) and an accumulated exposure grown. The two factors together deter- A consensus has developed among index (ppb-hours) as determinants of mine statewide yield losses (table 1). North American scientists that crops are damage. There is little doubt that ozone The equations that allow calculation likely to be damaged by ozone when reduces crop yields at current ambient of these yield losses have been derived concentrations greater than 60 ppb ex- concentrations. mostly using open-top field-exposure ceed a total of 20,000 ppb-hours over any Yield loss in tomato. In 2001, chambers (OTCs)(Heagle et al. 1988). 90-day period (Heck and Furiness 2001). California produced 93% of U.S. pro- While OTCs may subtly alter the crop A similar consensus in Europe finds cessing tomatoes, mostly in the San microenvironment and subsequent that crops are likely to be damaged by Joaquin and Sacramento valleys. plant growth (Manning and Krupa ozone when concentrations greater than California’s combined processing and 1992), they did not significantly affect 40 ppb exceed a total of 3,000 ppb-hours fresh-market tomato crop is valued crop yield in 70% of published experi- (Karenlampi and Skarby 1996). These at approximately $766 million (CDFA ments (Legge et al. 1995). In addition, conclusions differ in magnitude due 2002). Tomato is only moderately sen- crop sensitivity to ozone was generally to differences in cultivars and growth sitive to ozone (Temple, Surano, et al. unaffected in the few cases where direct environments on the two continents. 1985). Statewide yield losses due to comparisons with alternative exposure However, they are similar in adopting ozone in 1993 (the last year available) were an estimated 6.8% for processing tomatoes and nearly none for fresh- market tomatoes (table 1). Yield loss in cotton. In contrast, cotton is relatively sensitive to ozone (Grantz 2003). Yield reductions have been demonstrated for upland cotton cultivars (Olszyk et al. 1993; Temple, Taylor, et al. 1985), with statewide

Mark Crosse © The Fresno Bee, 2004 yield losses in 1993 estimated at 23.3% (table 1). The ﬁrst Pima cotton cultivars introduced into the San Joaquin Valley, including cv. S-6, were affected even more (Olszyk et al. 1993). More recent Pima cultivars — selected under ozone pressure in the San Joaquin Valley — are reportedly more resistant to ozone, but conﬁrming data is unavailable. Weed and crop competition Herbicides are used on much of the The San Joaquin Valley is now the nation’s most polluted air basin. While Southern Califor- tomatoes (Lycopersicon esculentum Mill.) nia air quality has improved remarkably in recent years, the increasing number of automo- and cotton (both upland [Gossypium biles in the Central Valley has led to more days like this one in Fresno. hirsutum L.] and Pima [G. barbadense L.]) DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 139 A B

Effect of increasing ozone concentration (left to right: about 15, 80 and 150 ppb) on growth of (A) Pima cotton and nutsedge grown in direct C competition with one nutsedge per cotton; (B) tomato and nutsedge grown in direct competition with nutsedge (two-to-one); and (C) yellow nutsedge grown in the absence of competition.

grown in California, preventing sub- underground by tu- stantial crop losses (CDPR 2002). At the bers, its adaptation to same time, ozone may profoundly affect ozone may be slower these plant communities, altering the than that of the more growth and fitness of both weedy and common sexually crop species as well as their competitive propagated weeds. interactions. While ozone impacts on Yellow nutsedge is many important crop species have been well established in the characterized, there are few reports on San Joaquin Valley, but the impacts of ozone on the growth no data is available on and fecundity of weeds (Fuhrer and this pest’s response to Booker 2003). Short life cycles and pro- ozone. We conducted lific reproduction could accelerate weed a series of experiments adaptation to ozone, and the enhanced at KREC on the interactions of nutsedge mean exposures) of ozone were imposed: competitive advantage of weeds relative with tomato and cotton. about 15 ppb (low ozone, atmospheric to crop species could increase herbicide background), 80 ppb (medium ozone, Exposure of plants to ozone use. However, the impacts of ozone on worst-case local ambient conditions) and such competitive systems cannot be pre- Processing tomato (nursery trans- 150 ppb (high ozone). dicted simply from the ozone sensitivi- plants of cultivars HD 8892 and EMP Plants were harvested prior to flow- ties of the individual species (Evans and 113), cotton (seeds of cv. Pima S-6) and ering at 1 to 2 months after planting, Ashmore 1992). It is important to con- nutsedge (locally collected juvenile separated into shoots and roots and sider the mechanisms of plant competi- plants that were about 2.5 inches [6 cen- dried at 160°F. The root fraction in nut- tion and ozone effects on interactions timeters] tall with two or three leaves) sedge was separated into roots (which that may emerge only when weeds and were grown in outdoor OTCs during included some rhizomes) and tubers, crops are grown together. summer 2003, in 2-gallon (9-liter) pots which were weighed separately and Yellow nutsedge (Cyperus esculentus of sintered clay (“kitty litter,” 6-40 counted. In pots containing two species L.) has become a particularly difficult mesh), irrigated twice daily and fertil- the roots were entangled, so the com- and costly weed to control in many ized weekly (Miracle-Gro, 0.17 ounce bined root mass was obtained.

California cropping systems. It is a C4 per gallon [1.3 grams per liter]). The experiment was performed species, making it water efﬁcient and Nutsedge-to-crop plant ratios in each twice with tomato and once with cot- heat tolerant, and thus well adapted to pot were zero-to-one and one-to-zero ton, each time with four replicate plants irrigated agriculture in the San Joaquin (single species), and one-to-one, two-to- per treatment. The experimental design Valley. Because yellow nutsedge is pre- one and three-to-one (competition within was four population ratios as subtreat- dominantly vegetatively propagated each pot). Three concentrations (12-hour ments within each of the three ozone DRAFT140 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 Fig. 2. Effect of increasing ozone exposure on percentage inhibition of shoot and root biomass productivity and on the resulting root-to-shoot biomass ratio (R/S) of tomato, cotton and nutsedge, grown without compe- Fig. 3. Effect of ozone exposure and nutsedge competition on tition. Shoot biomass of cotton was reduced shoot biomass production of tomato and cotton grown alone or by ozone at P = 0.0007. Root biomass of cot- with nutsedge (averaged over all levels of nutsedge competition).

ton and tomato were reduced by ozone at Tomato grown alone and with nutsedge was reduced by ozone at P = 0.0002 and P = 0.0955, respectively. R/S P = 0.09 and P = 0.08, respectively. Cotton was far more sensitive,

declined in each case but was not signiﬁcant and was reduced by ozone at P < 0.0001 both in the presence and in any species. absence of nutsedge.

concentrations. Species were analyzed dium ozone reduced leaf area and plant generally been found to inhibit biomass separately. Data were transformed as re- height only modestly, and in these ex- production and reduce R/S in tomato quired and analyzed using PROC GLM periments did not affect shoot biomass (Varshney and Rout 1998). Nutsedge. (General Linear Model; SAS). Mean production (fig. 3). Increasing levels of ozone separation was by Fisher’s Protected The biomass of cotton roots was had no significant effect on either shoot LSD. Levels of significance are presented reduced somewhat more than that of biomass (figs. 2A, 3) or root biomass (fig. in the figure legends, and the bars in shoots (fig. 2B), particularly at high 2B) of nutsedge. Plants were more erect figures 2 and 3 are labeled with different ozone. These coordinated changes in at medium than low ozone due to the letters if differences within a species are root and shoot biomass led to a small, presence of stiff flowering stalks, which significant at P < 0.10, a more permis- nonsignificant decline in the root-to- were only occasionally observed at low sive standard than the more common shoot biomass ratio (R/S; fig. 2C). or high ozone. As the ozone concentra- P < 0.05 to accommodate the modest Significant declines in R/S of cotton tion increased further, the nutsedge responses in the ozone-tolerant tomato. have been observed previously at simi- leaves became more flaccid and plant An additional statistical contrast was lar ozone concentrations (Grantz 2003). height declined. Reduced plant stature conducted between plants grown alone Tomato. Growth was less sensitive to has obvious implications for light inter- and with competition (averaged over all ozone in tomato than in cotton, particu- ception by nutsedge in competition with population ratios). larly at the highest ozone concentration. crop plants. As in tomato and cotton, Shoot biomass was reduced by about R/S of nutsedge declined as expected but Effects on individual species 19% at medium ozone with little further the change was not significant (fig. 2C). Cotton. As expected from our pre- decrease at high ozone figs. 2A, 3). Root The production and size of nutsedge vious studies (Grantz 2003), elevated biomass was reduced more than shoot tubers did not respond consistently to ozone negatively affected growth of biomass, by about 30% at high ozone ozone in these experiments, and increased the cotton plants, which were about compared with low ozone (fig. 2B). The in many plants. Further studies are under 25% shorter and produced 50% fewer declines in tomato root and shoot bio- way to determine if elevated ozone con- leaves. The highest ozone concentration mass were sufficiently well balanced, centrations stimulate biomass allocation to also reduced cotton shoot biomass by as in cotton, that the decline in R/S the reproductive tubers, as predicted from about 86% (figs. 2A, 3). In contrast, me- was not significant (fig. 2C). Ozone has other plant responses to abiotic stress. DRAFThttp://CaliforniaAgriculture.ucop.edu • APRIL–JUNE 2005 141 Photos: Jack Kelly Clark

A significant but hidden aspect of ozone crop damage is reduced growth below- was more sensitive to ozone than tomato, ground, demonstrated here following expo- Weed competition with crops sure of plants to elevated ozone levels. Left, the shoot biomass of tomato was most an intact cotton root system is scanned into Cotton and nutsedge. At the low affected by competition with nutsedge at a computer for an automated analysis of ozone concentration, competition low ozone (P = 0.055)(fig. 3). root length and morphology. Right, ozone with nutsedge — averaged over all Tomato root productivity was more causes changes in cotton root respiration, measured with a computerized oxygen elec- population ratios — reduced the shoot sensitive to ozone (30% reduction; P = trode system. biomass of cotton by 22% (fig. 3). At 0.096) than nutsedge root productivity medium ozone, cotton was slightly was (19% reduction; not significant) more sensitive than nutsedge, particu- (fig. 2B). At medium ozone, tomato root larly belowground, and the loss due biomass declined by 20% while nut- of the impact of ozone on the complex to nutsedge competition was closer to sedge was unaffected. interactions that characterize agroecosys- 50%. At high ozone, the relative loss The nutsedge shoots in the high- tems, including the ozone sensitivity of due to nutsedge competition was simi- est ozone concentration drooped over crops, competing vegetation and other lar to that at medium ozone, although the side of the pots, further decreasing pest species, and on the dynamics and cotton growth was reduced to very low nutsedge competition for light. As ob- mechanisms of specific competitive rela- levels even in the absence of competi- served previously for the interactions tionships among these species. So far, this tion. This reduction in cotton growth of these two species (Santos et al. 1997), important work has only just begun. The by the presence of nutsedge (P = 0.005) tomato had a competitive advantage exposure facilities recently completed in reflected the greater weakening of cot- over nutsedge in light interception. In the new research greenhouse at KREC ton than nutsedge by ozone and the our studies, this advantage increased will allow us to bring further quantitative resulting enhanced vigor of nutsedge with ozone concentration. Tomato was techniques to bear, particularly on the grown in direct competition (fig. 3). more sensitive to ozone than nutsedge, belowground competition between these This was particularly true at medium particularly near ambient (medium) crop and weed species. ozone because at high ozone nutsedge ozone, but nutsedge was more sensitive In the Pima cotton-nutsedge system, was also affected and appeared to be to competition than tomato. cotton was more strongly affected at high less competitive with cotton. Nutsedge ozone concentrations than nutsedge, was Air pollution and agriculture inhibited cotton growth much more at more inhibited by nutsedge competi- high than at low ozone. Ozone air pollution continues to be tion, and was less able to compete with Tomato and nutsedge. At the low problematic in rural areas such as the nutsedge at near ambient (80 ppb) ozone ozone concentration, competition — av- San Joaquin Valley. Single-factor ozone concentrations than in clean (15 ppb) air. eraged over all population ratios — re- exposure experiments have consistently In the tomato-nutsedge system, tomato duced tomato shoot biomass by about indicated that ozone now causes eco- was only moderately sensitive to ozone 15% (fig. 3). However, in contrast to cot- nomically significant losses in the yields compared with cotton or nutsedge, com- ton, at medium ozone there was no ad- of most crops, and this will get worse if peted well with nutsedge at all levels of ditional impact of nutsedge competition current trends in rural population density ozone, and did not lose any competitive on tomato growth. The reductions of bio- continue. This conclusion is unlikely to advantage with rising ozone concentra- mass by medium ozone and by competi- change with further research. More com- tion. Nutsedge tuber production may tion were similar and not increased by plex, multifactor experiments are now have increased at high ozone concen- the combination of both stresses. At high required to allow more accurate estimates trations. This weed may become more ozone there was little further effect on to- of current losses in specific crops, and to difficult to control, spread more rapidly mato alone but a slight increase in the in- provide a basis for predicting losses in and require greater use of herbicides or hibition of tomato shoot biomass due to future presumably warmer climates. In other control strategies, particularly in nutsedge competition. Because nutsedge particular, this will require consideration ozone-sensitive crops such as Pima cot- DRAFT142 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2 Yellow nutsedge may become more difficult to control, spreading more rapidly and requiring greater use of herbicides, particularly in ozone- Jack Kelly Clark sensitive crops such as Pima cotton.

tion. Sacramento, CA. 180 p. 69:192–205. [CDPR] California Department of Pesticide Manning WJ, Krupa SV. 1992. Experimen- Regulation. 2002. Annual Statewide Pesticide tal methodology for studying the effects of Use Report. www.cdpr.ca.gov. ozone on crops and trees. In: Lefohn AS (ed.). Evans PA, Ashmore MR. 1992. The effects Surface Level Ozone Exposures and Their Ef- of ambient air on a semi-natural grassland fects on Vegetation. Chelsea, MI: Lewis. community. Agric Ecosyst Environ 38:91–7. p 93–156. Fuhrer J. 2003. Agroecosystem responses Murphy JJ, Deluki MA, McCubbin DR, et

to combinations of elevated CO2, ozone and al. 1999. The cost of crop damage caused by global climate change. Agric Ecosyst Environ ozone air pollution from motor vehicles. 97:1–20. J Environ Mgmt 55:273–89. Fuhrer J, Booker F. 2003. Ecological issues Mutters R, Soret S. 1998. Statewide poten- ton. These results indicate the variety of of ozone: Agricultural issues. Environ Intl tial crop losses from ozone exposure. Final 29:141–54. Report to California Air Resources Board on impacts that climate change, including Grantz DA. 2003. Ozone impacts on cot- Contract 94–345. www.arb.ca.gov/rd/rd.htm. rising ground-level ozone, may have on ton: Towards an integrated mechanism. Envi- Olszyk DM, Bytnerowicz A, Kats G, et al. important crop production systems. ron Pollut 126:331–44. 1986. Crop effects from air pollutants in air Heagle AS, Kress LW, Temple PJ, et al. exclusion systems vs. field chambers. J Envi- 1988. Factors influencing ozone dose-yield ron Qual 15:417–22. response relationships in open-top field Olszyk D, Bytnerowicz A, Kats G, et al. chamber studies. In: Heck WW, Taylor OC, 1993. Cotton yield losses and ambient ozone D.A. Grantz is Director, UC Kearney Ag- Tingey DT (eds.). Assessment of Crop Loss concentrations in California’s San Joaquin ricultural Center, and Air Pollution Effects from Air Pollutants: Proceedings of an Inter- Valley. J Environ Qual 22:602–11. Specialist and Plant Physiologist, Depart- national Conference; October 1987, Raleigh, Santos BM, Bewick TA, Stall WM, et al. NC. New York: Elsevier Appl Sci. p 141–79. 1997. Competitive interactions of tomato ment of Botany and Plant Sciences and the Heck WW, Furiness CS. 2001. The effects (Lycopersicon esculentum) and nutsedges Air Pollution Research Center, UC Riv- of ozone on ecological systems: Time for a (Cyperus spp.). Weed Sci 45:229–33. erside; and A. Shrestha is Integrated Pest full assessment. Environ Mgr (Oct):15–24. Spash CL. 1997. Assessing the economic Management Weed Ecologist, UC Statewide Karenlampi L, Skarby L. 1996. Critical levels benefits to agriculture from air pollution for ozone in Europe: Testing and finalizing control. J Econ Surv 11:47–70. IPM Program. Both are located at the UC the concepts. UN-ECE Workshop Report. Univ Temple PJ, Surano KA, Mutters RG, et al. Kearney Research and Extension Center, Kuopio, Dept Ecol Environ Sci. Kupio, Finland. 1985. Air pollution causes moderate damage Parlier. We gratefully acknowledge support Kim HJ, Helfand GE, Howitt RE. 1998. An to tomatoes. Cal Ag 39(3-4):20–2. economic analysis of ozone control in Cali- Temple PJ, Taylor OC, Benoit LF. 1985. Cot- from the USDA National Research Initia- fornia’s San Joaquin Valley. J Agric Resource ton yield responses to ozone as mediated by tive through award 00-35100-9181. Econ 23:55–70. soil moisture and evapotranspiration. J Envi- Legge AH, Grunhage L, Nosal M, et al. ron Qual 14:1. References 1995. Ambient ozone and adverse crop re- Varshney CK, Rout C. 1998. Ethylene di- [CDFA] California Department of Food sponse: An evaluation of North American urea (EDU) protection against ozone injury in and Agriculture. 2002. Resource Directory; and European data as they relate to expo- tomato plants at Delhi. Bull Environ Contam California Agriculture: A Tradition of Innova- sure indices and critical levels. Angew Bot Toxicol 61:188–93.

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Julie Morrison Stream temperature monitoring Under the Clean Water Act, hundreds of miles of California waterways must reduce elevated water temperatures in order to improve cold-water fish habitat. Stream temperatures may be increased due to the diversion of irrigation water for pastures, the return of warm irrigation runoff to streams, or the reduction in canopy cover over streams due to logging and grazing. In the next issue of California Agriculture, scientists use a case study from two Modoc County streams to demonstrate how water-temperature monitoring data can be better analyzed and graphically presented, and how relationships between temperature and factors such as flow, canopy cover and air temperature can be identified and quantified. In a related article, a case study near the same streams illustrates how land managers can assess and monitor water-quality impacts related to agricultural discharges from irrigated pasture. Also:

Streamﬂow and tree canopy are important factors determining Using GPS to pinpoint herbicides summer water temperatures in Lassen Creek, which is critical ▼ spawning and rearing habitat for Goose Lake redband trout. Soil microbial communities

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144 CALIFORNIA AGRICULTURE, VOLUME 59, NUMBER 2