Western Plant Diagnostic Network1

First Detector News A Quarterly Pest Update for WPDN First Detectors Fall 2017 edition, volume 10, number 4

In this Issue Dear First Detectors, Our Fall newsletter is a little late due to

Page 1: Editor’s comments colds and flus circulating around the University of California, Davis, and a few new developing stories! Pages 2 – 4: Tomato crown rot disease spreading to new This edition discusses two tomato diseases, one fungal areas (tomato crown rot) and the other caused by a viroid (tomato chlorotic dwarf). Both are dangerous diseases for the Pages 5 - 6: Tomato chlorotic tomato industry. Medflies have invaded California once dwarf viroid in Hawai’i again, with outbreaks in Solano, Los Angeles, and San Mateo counties. They just keep coming! A new virus is infecting Pages 7 - 8: Three Medfly grapes in Washington – tobacco ringspot virus. This virus not quarantines in CA only infects tobacco, but several other hosts, including many fruit crops and grapes. Huanglongbing, the fatal citrus Pages 8 – 9: New virus disease of grapes in WA bacterial disease vectored by the Asian citrus psyllid, is steadily spreading in southern California. Page 10: Asian citrus psyllid and huanglongbing bacterial I have an erratum to confess. In the Summer 2017 edition I disease spread in CA identified this pallet marking as Canada (CA). CN stand for China. I heard from several USDA Plant Contact us at the WPDN Regional Center at UC Davis: Protection and Quarantine folks. Thanks Phone: 530 754 2255 to them for paying attention!

Email: [email protected] Web: https://wpdn.org Editor: Richard W. Hoenisch Please find the NPDN family of newsletters at:

@Copyright Regents of the Newsletters University of California All Rights Reserved

Western Plant Diagnostic Network News

Tomato Crown Rot Disease Spreading to New Areas 2

By Cassandra Swett and Joe Nunez

This was a big year for southern blight in California crops. Out of over forty crown rot samples received in the UC Davis Vegetable and Agronomic Crop Pathology program (Swett lab) in summer 2017, 50% were southern blight, 40% were Fusarium root and crown rot, and 10% were attributed to other causes. This disease was reported to cause over 50% mortality in affected fields.

Why is it called “Southern Blight?”

Southern blight, also known as "southern wilt" and "southern stem rot" is a serious and frequent disease of many vegetable and agronomic crops in southern regions of the US including Southern California, Virginia, Alabama, and the Coastal Plain and Piedmont areas of North Carolina. It is caused by the soil-borne fungus, Athelia rolfsii (previously called Sclerotium rolfsii) and attacks a number of crops including cantaloupe, carrot, onion, pepper, potato, sweet potato, tomato, watermelon and others. In addition, several field crops such as cotton, bean, peanut, soybean, and tobacco are affected. The disease usually appears in "hot spots" in fields starting in mid-summer and continues until cooler, dryer weather prevails. Losses may vary from light and sporadic to almost total destruction of the crop. The fungus may also decay harvested produce, especially carrots.

Southern blight is a very destructive, fast acting crown rot disease that rapidly kills the plant. Over 500 different plants are southern blight hosts. In 2017, affected crops in California included pepper, potato, tomato, cucumber, canary bean, chard, and sunflower. Southern blight is not typically considered to be a widespread problem in California--major impacts are usually restricted to the Kern County area. Unusually, in 2017 this disease also caused major losses in many more northern counties in the San Joaquin and Sacramento valley, where it is not typically an issue, including Colusa, Yolo, Contra Costa, San Joaquin, and Merced.

The widespread distribution we saw this year is not likely due to pathogen spread to new fields, since the pathogen is widely distributed. Southern blight is favored by high temperatures (over 86°F), high soil moisture, dense canopies, and frequent irrigation. It seems most plausible that a combination of late planting dates and record high summer temperatures created unusually favorable conditions for the pathogen across a wider geographic range.

The increased damage from the disease this year may mean that this will be a bigger issue next year if the environme nt is conducive and the disease is not properly managed. The A. rolfsii fungus survives in soil as hardened structures called sclerotia for at least five years. Each infected plant can literally produce tens of thous ands of sclerotia and then become more widely distributed in a field with each successive field operation. Although this disease may initially only affect a few plants in the field, southern blight can be serious enough to cause significant yield loss within a season or two. With a host range of over 500 plants, this fungus can easily persist from year to year in infected crop debris.

Cassandra Swett, Ph.D., is an assistant specialist in the UCCE and lecturer, at UC Davis. Her specialties are fungal pathogen ecology in vegetables and field crops and effects of adaptive water use on plant-pathogen interactions. Joe Nunez, M.S. is a farm advisor, emeritus,

in Kern County, CA. Western Plant Diagnostic Network News

Cassandra Swett Joe Nunez

How to identify southern blight in the field 3

Southern blight misdiagnosis is likely if it occurs in an area where it has not historically been an issue. Scouting and mapping infested locations in fields during the summer months will greatly help in

determining what options can be taken before the sclerotia levels become too numerous and cause severe crop loss. It can be easy to confuse southern blight with other crown rotting diseases, for example Fusarium crown rot of tomato and white rot of onions and garlic. Accurate diagnosis is critical to effective control. You can distinguish southern blight in the field based on the following diagnostic traits, one or more of which is often, but not always present. Part of the trick to diagnosis is not to just look at the plant,

but also look at the soil right around the crown.

J.Nunez J. Nunez J.

These small tan to reddish brown sclerotia form White fan like mycelium (thread like) growing on at the base of the plant and / or in the soil right the crown / affected tissues. Severely affected around the plant. The sclerotia look like alfalfa plants can have vascular discoloration, which may seeds when young but turn brown with age. be confused with Fusarium wilt.

J.Nunez

C. Swett C.

Plants go from looking healthy to dead in less White fungal mycelium growing INTO the soil.

than a week No other fungus will grow extensively in the soil. Sometimes you also see sclerotia in the soil Western Plant Diagnostic Network News

4 In-season fungicide applications Southern blight acts fast, so as soon as you detect the problem, it is critical to get out there to spray. Fungicides work by covering the crown tissue both above and below the soil, killing the fungus around the crown. For vegetable crops, fungicides such as flutolanil , penthiopyrad , and tebuconazole are known to be effective in the management of southern blight. However these products are registered on only a few vegetables so make sure to check crop registration before using these on any vegetable crop. Also, some of these fungicides have severe plant-back restrictions, so crop rotations need to be carefully planned. As always, make sure to read and follow label directions to avoid any problems. Perhaps the biggest obstacle to fungicide control of southern blight is application timing and method. Because southern blight is basically a summer time disease it rears its ugly head when most crops are near maturity with a full canopy cover. Getting fungicides to the base of the stem and onto the surface of the soil is very difficult especially for fields on drip irrigation systems. Chemigation through sprinklers is a better option especially on crops like garlic and onions which do not have a dense canopy. If the crop has a dense canopy that the fungicide cannot penetrate, then a fungicide application will not work to control the disease. Fungicide control is most effective in narrow canopy crops, including onions, garlic, beans, sunflower, and to a certain extent, pepper and potato. In dense canopy crops such as tomatoes, melons, and vegetables grown for seed like lettuce, fungicide applications are only effective early in the season, before the canopy expands.

Crop Rotation

If you have detected southern blight in your field, one of the best things you can do the following year is to plant a narrow canopy crop that you can effectively manage with fungicides. The disease can be effectively controlled in these crops, preventing sclerotia from increasing. Rotations with non-host crops are limited because of the wide host range of the pathogen. Poor-host crops such as corn and small grains (wheat, millet, oats) can help to significantly reduce sclerotia levels in the field. Most if not all of these crops can become infected by the fungus, but either they are not good hosts and/or the environmental conditions during the growing season are not conducive to pathogen growth. For instance, wheat can be a host, but it’s typically too cold for fungal growth during the time that wheat is grown. On the other hand, rotation with highly susceptible crops / cover crops such as legumes such (g. beans, peas and hairy vetch) can greatly increase soil infestation levels. Mustard cover crops can suppress southern blight, and may be useful for organic producers, where fumigation is not an option.

Pre-plant soil treatment strategies Fumigation with metam sodium metam sodium is the most effective way to reduce the amount of sclerotia in the soil, but is unlikely to eliminate the inoculum completely unless applied through the sprinklers, a practice that is restricted in many counties.

Solarization alone is not generally considered a viable management strategy, but when soils are solarized before addition of a biological control or a fungicide, disease can be reduced by 70-100% compared to the same biological or chemical treatment without solarization. Make sure to prepare the soil for planting before solarizing, since cultivation and the incorporation of amendments can bring buried sclerotia back to the upper soil layers. Deep plowing will bury the sclerotia and get it away from attacking plants at the soil line. Sclerotia deeper than 6 inches are usually parasitized by other microbes and are killed over time. Of course, plowing is not an option for fields where buried drip irrigation systems are already installed. Sclerotia near the surface of the soil can be killed when exposed to high temperatures (105-120°F) for two to four weeks during the summer months.

Western Plant Diagnostic Network News

Tomato Chlorotic Dwarf Viroid in Hawai’i 5

by Alejandro Olmedo-Velarde, Randall T. Hamasaki, Brian Bushe, and Michael J. Melzer Department of Plant and Environmental Protection Sciences University of Hawai’i, Manoa

Tomato (Solanum lycopersicum) is an important vegetable crop in Hawai‘i, grown in field and greenhouse operations. It is also a common host of many pests and pathogens in Hawai‘i, including mites, insects, fungi, nematodes, bacteria, and viruses. Another group of pathogens, known as viroids , are also a major hindrance to tomato production around the world. Until recently, there have been no reports of viroid infection in tomato or any other crop in Hawai‘i. In 2017, however, a disease caused by Tomato chlorotic dwarf viroid (TCDVd) was identified in greenhouse- grown tomato for the first time in the state.

Symptoms in tomato

Symptoms caused by TCDVd can vary in severity depending on the tomato variety and environmental conditions. Typical symptoms include stunting of the plant by reduction in internode length, as well as foliar irregularities such as chlorosis, necrosis, purpling of leaflets, and epinasty (downward curling of the leaflet margin). The symptoms caused by TCDVd can be the same as those caused by other viroids (co)-infecting tomato such as Columnea latent viroid, Potato spindle tuber viroid , and Tomato apical stunt viroid. Tomato plant showing stunted growth and chlorotic foliage with downward curling of leaves and leaflets Spread of TCDVd

TCDVd is primarily spread plant-to-plant by grafting, contaminated tools, and leaf or stem contact of neighboring plants. Even touching a healthy plant after an infected plant can result in transmission. There are no insect vectors known to spread TCDVd, although it is possible that chewing insects and bumblebees can spread viroids from plant to plant in a manner similar to mechanical transmission. TCDVd can enter the seed of infected plants, resulting in infected seedlings after germination. The local, regional, or global distribution of infected seed represents the most likely pathway for long-distance spread of the pathogen. Host Range of TCDVd

In addition to tomato, TCDVd has been found in petunia (Petunia x hybrida), trailing verbena (Verbena x hybrida), dwarf periwinkle (Vinca minor), and scarlet angel’s trumpet (Brugmansia sanguinea). Laboratory inoculation experiments indicate TCDVd is also able to infect ornamental flowers such as lobelia (Lobelia erinus), marigolds (Calendula officinalis, Tagetes spp.), and dahlia (Dahlia spp.), as well as pepper (Capsicum annuum), eggplant (Solanum melongena), and several weed and herbaceous species such as jimsonweed (Datura spp.), Nicotiana spp., and other solanaceous plants (Solanum spp.).

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Current Geographic Range of TCDVd

TCDVd was first discovered in tomato seedlings grown in Manitoba, Canada, from seed imported from the Netherlands. Symptoms resembled those caused by a related but distinct viroid, Potato spindle tuber viroid

(PSTVd). TCDVd has since been found in India (2006), Czech Republic (2008), Mexico (2008), Japan (2008), France (2010), Slovenia (2011), and Norway (2012). In some of these locations, TCDVd has only been found in petunia plants. In the USA, TCDVd has been found infecting greenhouse tomatoes in Arizona and Colorado. The viroid has been successfully eradicated in several of these locations.

Management of TCDVd

TCDVd is a pathogen that can be successfully managed and even eradicated. For both greenhouse and field operations, sanitation is of critical importance. Once it has been confirmed that TCDVd is present in a farm or garden, all host plants in the area, whether visibly affected or not, should be immediately removed or destroyed. Plants can be a sprayed with an approved herbicide or buried, since the viroid will not survive or remain viable in dead plants. If tilling plants under with farm equipment, be sure to thoroughly clean and disinfect equipment after working in areas with diseased plants. Workers should wear gloves and protective suits when removing infected plants. These should be removed and disposed of before working with healthy plants. This will prevent spread of the viroid through contaminated hands or clothing. In greenhouse operations, once the infected and surrounding plants are removed, the pots, medium, and/or hydroponic equipment should be either replaced or thoroughly sanitized using an effective disinfectant. All tools such as pruning shears should also be replaced or thoroughly sanitized by heat (using a propane torch) or disinfectant after use. Studies have shown that 2% Virkon S (DuPont) or fresh (made daily) 10% bleach solutions are effective at sanitizing tools, even with short exposure periods (<10 seconds). If possible, a disinfectant should be run through irrigation or hydroponic systems, followed by clean water.

Once infected plants have been removed from an area and tools and equipment have been sanitized, it is essential to continue monitoring for newly infected plants to prevent re-establishment of the viroid. Seeds and seedlings should be obtained only from reputable sources and certified to be free of TCDVd and other pathogens. Hand tools should be regularly sanitized during pruning or harvesting. Ideally this tool sanitation should be done before working on a new plant.

All photos by Mike Melzer, Ph.D., University of Hawaii, Manoa

Left: chlorosis on tomato leaflet margins, and right: stunting and chlorosis on the entire tomato plant

Western Plant Diagnostic Network News

Three Mediterranean Fruit Fly Quarantines in California 7

Solano County CA

A Mediterranean fruit fly (Medfly), Ceratitis capitata , infestation in Solano County, CA, reported first on October 11, 2017, has triggered an 85-square mile quarantine that encompasses Travis Air Force Base, California. This is a species of fruit fly capable of causing extensive damage to a wide range of fruit crops. It is

native to the Mediterranean area, but has spread invasively to many parts of the world, including Australasia and North and South America. Adult medflies lay their eggs under the skins of fruit, particularly where the skin is already broken. The eggs hatch within three days, and the larvae develop inside the fruit. While established in Hawaii , the US mainland infestations are quarantined and aggressively treated to prevent establishment. The Medfly can infest more than 250 types of fruit and vegetables! See more Medfly images!

In response to the location of the Medfly, the California Department of Food and Agriculture (CDFA), working with the USDA to determine if this fly represents a breeding population. 1,095 insect traps have been placed as part of a delimitation survey. Medfly traps are placed in consecutive circles extending several miles in each direction from the original Medfly detection site. In this instance, the traps cover 81 square miles. The quarantine map for all three outbreaks: http://www.cdfa.ca.gov/plant/medfly/regulation.html. The Summer 2013 newsletter has a feature article on “Exotic Fruit Flies”.

FLDivision of Plant Industry

Bruce Daniel Feliciano Daniel

A male Medfly A Medfly larva Medfly larvae feeding on orange

Los Angeles County Quarantine

A quarantine has been declared on September 14, 2017, due to a Mediterranean fruit fly (Medfly) infestation detected in the Sun Valley neighborhood in northern Los Angeles County. Two adult males, nine females, and 55 larvae have been detected. The USDA, the Los Angeles County Agricultural Commissioner, and the CDFA are working collaboratively on the eradication.

The 89-square mile quarantine is in the northern San Fernando Valley of Los Angeles County, northwest of the City of Burbank. It is bordered on the north by the Angeles National Forest; on the south by Griffith Park; on the west by I-405; and on the east by the Verdugo Mountains. Increased numbers of sterile male Medflies are being released in the area as part of the eradication effort. In addition, properties within 200 meters of detections are being treated with an organic formulation of Spinosad, which originates from naturally- occurring bacteria, in order to eliminate any mated females and reduce the density of the population. The flies lay their eggs in fruit, so crews will also remove fruit from trees within 100 meters of sites where larvae and

multiple adult flies have been found. FullertonArboretum

Medfly close up! Western Plant Diagnostic Network News

San Mateo County CA 8

SACRAMENTO, December 19, 2017 – A portion of San Mateo County has been placed under quarantine for the Mediterranean fruit fly (Medfly) following the detection of two Medflies within the City of Half Moon Bay. CDFA is working collaboratively with the USDA and the San Mateo County Agricultural Commissioner’s office on this project. The quarantine area measures 56 square miles, bordered on the north by San Vicente

Creek; on the south by Lobitos Creek Road; on the west by the Pacific Ocean; and on the east by Lower Crystal Springs Reservoir.

Sterile male Medflies will be released in the area as part of the eradication effort. The release rate will be 500,000 males per square mile per week in a 12 square mile area around the infestation. In addition, properties within 200 meters of detection sites are being treated with an organic formulation of Spinosad, which originates from naturally-occurring bacteria.

Sterile male Medflies are provided by the joint CDFA/USDA sterile insect rearing facility in Los Alamitos, which prepares sterile files for release every day over the Los Angeles basin. The sterile release program has a proven track record of success in California. Sterile male flies mate with fertile female flies in the natural environment but produce no offspring. The Medfly population decreases as the wild flies reach the end of their natural life span with no offspring to replace them, ultimately resulting in the eradication of the pest.

Washington Grape Grower Battles New Threat

A virologist with Washington State University’s (WSU) Viticulture and Enology program has discovered a block of Grenache noir vines are stunted and sickly because they suffer from a damaging syndrome caused by tobacco ringspot virus (TRSV), a pathogen never before seen in Washington.

“That was a huge surprise,” says Naidu Rayapati “It was a revelation that we have a new problem here.”

WSU

Grapes from healthy Grenache noir vines (left) smaller grapes and clusters (right) from vines damaged by tobacco ringspot virus

The problem was initially discovered by vineyard manager Andrew Schultz on grapevines planted in a former pear orchard near Wapato, WA. The Grenache noir vines had been productive and healthy, but over time, a mysterious infection had taken hold. Mottled, stunted, and sickly, the infected vines were producing only tiny, miniature clusters — or no fruit at all. Infected leaves, crisscrossed with white lines, looked as if they had been munched by insects, but Schultz could see none.

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Discovered 90 years ago in Virginia, TRSV affects a wide variety of crops, from grapes, apples, and cherries to common weeds. It is spread by nematodes — specifically, the dagger nematode, Xiphinema americanum. Like the virus, this species of dagger nematodes was also previously unknown in Washington. Rayapati and Schultz aren’t sure how the virus and its nematode vector arrived here, but Rayapati suspects they may have hitched a ride with pears or other crops years ago. TRSV causes vines to become totally unproductive with time. The nematode and virus persist in Professor Naidu Rayapati the soil for many years.

Since the discovery of TRSV in Grenache noir in 2013, the virus remains isolated in that single vineyard block in Wapato. The dagger nematode can transmit the virus from infected vines to healthy ones. The soils are sandy, which aid in the dispersal of nematodes in general, as they “swim” between the sand grains. Rayapati and Schultz are testing different combinations of rootstocks and grafts, as well as own-rooted vines, to find grape plants that resist the virus or are unpalatable to nematodes. Schultz is also looking at predatory nematodes that eat the ones spreading the virus. TRSV has a broad host range and can jump easily from one plant species to another. “We’re farming 50-year-old pear blocks that predate modern clean plant materials, and may someday be planted in grapes,” Schultz says. “We don’t know what viruses may be in the ground that do not affect pears, but may pop up when we plant grapes.” Wine is a $4.8 billion industry in Washington. Sixty thousand acres of wine grapes are grown in WA, with more planted every year.

WSU

WSU

Poor fruit set in TRSV infected Grenache noir Grenache noir vine infected with TRSV virus

CropIPM Ontario

Universityof Kentucky

Tobacco ringspot virus on tobacco Tobacco ringspot virus on tomato Western Plant Diagnostic Network News

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Asian Citrus Psyllid / Huanglongbing spread in California Citrus

Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (order Hemiptera : family Liviidae ), is a notorious pest of citrus because it vectors a phloem-dwelling plant pathogenic bacterium, Candidatus Liberibacter asiaticus that causes a lethal citrus disease, known as Huanglongbing (HLB), also called citrus greening. ACP and HLB are serious invasive species that cause immense economic losses in areas with important citrus industries. The citrus

industry in Florida had been severely impacted. The red dots are the where the Asian citrus psyllids have been found through October 23, 2017. The green dots where the ACP has been found in the Mexican states of Baja California and Sonora. The green outlined areas in California are the huanglongbing quarantine areas.

Please see the WPDN newsletters regarding the ACP/HLB spread: Summer 2010, Fall 2013, Summer 2015, Winter 2016, and Spring 2017. Between July 25 and September 28, 2017, the California Department of Food and Agriculture (CDFA) confirmed the presence of HLB from citrus tree tissue collected in the City of Riverside, Riverside County, CA. County agriculture officials reported the first case of the disease, which was found in a residential grapefruit tree near the Interstate 215/Highway 91 interchange. State officials said the tree was identified when several Asian citrus psyllids in the area tested positive for the bacteria that causes citrus greening. Until now, the only confirmed cases of HLB in Southern California have been in residential trees in Los Angeles and Orange counties. Experts have said it was only a matter of time before it showed up in the Inland Empire. The Asian citrus psyllid first appeared in the Southland in 2008. In 2012, the first case of HLB was identified in a tree in Hacienda Heights. Citrus material was illegally imported from Asia that was infected with the bacterium. In the meantime, the disease continues to spread in Los Angeles and Orange counties. Please see CDFA Interior Quarantine INDEX for the latest news on the spread of HLB.

Agriculture officials, the citrus industry and researchers have been pushing hard to find solutions to the problem. Efforts have included introducing biological controls, developing more effective insecticides, earlier detection of the disease — symptoms don’t usually show up for three years — and resistant strains of citrus plants. Please see the American Society of Phytopathology article on Citrus Huanglongbing. This includes the history of the disease and excellent images of HLB infected citrus.

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