UC Agriculture & Natural Resources California Agriculture

Title Mulches reduce aphid-borne viruses and whiteflies in cantaloupe

Permalink https://escholarship.org/uc/item/4wf766nd

Journal California Agriculture, 59(2)

ISSN 0008-0845

Authors Summers, Charles G. Mitchell, Jeffrey P. Stapleton, James J.

Publication Date 2005

Peer reviewed

eScholarship.org Powered by the California Digital Library University of California 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 eco- nomic 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, mid- dle, 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 strate- gies 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