Napa on Alert for New Grapevine Pest

Growers hear suppression plans for European moth, found on 32 properties

by Jon Tourney
European grapevine mother Napa
Napa County ag commissioner Dave Whitmer consults a map displaying locations where the European grapevine moth has been detected.
Rutherford, Calif. -- Napa County Agricultural Commissioner Dave Whitmer, along with state and federal officials, briefed 180 Napa Valley grapegrowers at a meeting this week about the status of the European grapevine moth (EGVM) (Lobesia botrana) and asked growers for cooperation in monitoring and suppression activities this year in efforts to prevent its spread, and potentially eradicate the pest.

The EGVM was found for the first time in the United States in Napa Valley in 2009, confirmed from a specimen collected in September. Area trapping, surveys by ag officials and specimens submitted by growers have confirmed the new invasive pest on 32 Napa Valley vineyard properties, primarily clustered near Highway 29 in the Oakville and Rutherford areas as far north as Zinfandel Lane. However, outlier EGVM specimens were found on three vineyard properties east of the City of Napa along 3rd Avenue near the Napa Valley Country Club.

Behind the scenes this winter, officials from the U.S. Department of Agriculture (USDA) and the California Department of Food and Agriculture (CDFA) have been working with Napa County to develop a joint EGVM Project to coordinate response activities for trapping, quarantine, treatments and public outreach. A Technical Working Group was formed and advised CDFA to conduct a statewide trapping survey that will begin Feb. 1 in Southern California and move north with trap deployment as seasonal weather changes. Trap densities will be 25 traps/square mile in commercial vineyards and five traps/square mile in urban areas.

In Napa Valley, traps will be in place by March 1 with densities of 25/square mile; however, in known infested locations densities will be 50/square mile. Once the EGVM's distribution is known, more definite recommendations and plans will be determined. The hope is that it is confined to Napa Valley, and eradication will be a viable option. Discussing the reasons for the meeting, Whitmer said, "This is a significant pest to deal with. I think we have one shot at eradication, and I'm optimistic we haven't missed that window. But it will require cooperation, and I hope you growers can do the things we ask you to do when we ask you to do them."


European grapevine moth
Adult European grapevine moths are less than 1/3-inch long. Photo by Jack Kelly Clark/University of California

Whitmer said there is some evidence to indicate the EGVM may have been in Napa Valley as early as fall 2008. The EGVM has some similarities with the light brown apple moth (LBAM), which also feeds on grape clusters. However, EGVM larvae and adults are smaller, and the EGVM larva burrows a hole and enters the interior of the grape berry.

EGVM biology and management

The EGVM was originally found in Italy and spread through Europe and the Mediterranean region in the 1800s. It's now found in North and West Africa, southern Russia and Japan. In 2008 it was discovered in Chile, where it is believed to have been brought in on rented vineyard equipment from France. The EGVM feeds on the flowers and fruit of grapes, rather than on leaves. Grapes are the preferred host, but other known plant hosts include olives, blackberries, gooseberries, cherries, peaches, nectarines, persimmons, plums, kiwis and pomegranates.
Napa County's UC Cooperative Extension viticulture farm advisor Monica Cooper discussed EGVM biology and management, noting that this information is based on what is known about the pest in other countries, since there is little experience with it in California. Cooper said the EGVM is expected to produce three generations during the growing season in Napa Valley. The EGVM adult moths fly at dusk, and mating occurs in flight just above the tops of grapevines, so traps need to be placed high in the vine canopy. Delta (tent) traps with a pheromone lure are used to trap adult moths during flight periods. Adult males are one-quarter inch long with tan-cream color wings, bluish-gray blotches, and brown and black markings.

The EGVM is currently in the overwintering pupal diapause stage (with pupae under vine bark surrounded by webbing), which lasts from October to March or April, depending on weather. The first moth flight could occur as early as March in Napa Valley, and the first generation is expected to develop from April to June. Females mate once during their lifetime and can lay from 80 to 160 elliptical, flat eggs. Eggs are laid singly, rather than in masses like the LBAM or omnivorous leafroller, on smooth surfaces of developing flower clusters in spring, and on berries during the second and third generations. Eggs are creamy white when laid, later turn yellow and then black when the head of the larva is formed. Larval size ranges from 0.04 inches long at emergence to 0.6 inches long fully grown. Young larvae are creamy white with black heads, and older larvae are tan to yellow-brown and can turn dark green or maroon as they mature.

Beginning in spring, traps should be checked weekly. When trap catch numbers peak for the first time, search for eggs on flower cluster stems. After egg hatch, look for webbing (or silk-like structures) and larvae on flower parts. The second moth flight is expected from June to July, with eggs laid on green fruit. The third moth flight is expected from July to August, with eggs laid on mature berries. Second- and third-generation larvae burrow inside berries, hollowing them out to leave the outer skin, and leaving webbing and excrement that also leads to fungal infections, particularly Botrytis in mature clusters later in the season. The EGVM caused some significant losses in 2009. A 9-acre Chardonnay vineyard in Oakville reportedly lost 40 tons of grapes damaged by moth larvae and infected with Botrytis.

Insecticide options

Cooper advised, "Focus on treating the first two generations heavily, so by the third generation the levels are as low as possible." Cooper listed several classes and types of insectides available as treatment options, depending on the moth's life stage. Ovicides must be applied before the egg is laid, and larvicides are most effective against young larvae. Intrepid (methoxyfenozide) acts as both an ovicide and a larvicide. Other larvicides include diamides such as Altacon and Belt, sodium channel blockers such as Avaunt, and spinosyns such as Success, Entrust, and Delegate. Microbial larvicides include two types of Bacillus thuringiensis (Bt), Dipel and Biobit, which are approved for organic use. Cooper said, "If you're using Bt, the application must be used when the larvae are feeding. Bt has a short residual period of three to five days, so you may need two applications, depending on seasonal conditions for the first generation." Ag officials will work with growers to determine appropriate control methods. Another option may be a pheromone twist tie attached to vines for mating disruption, but it is still going through registration for use in California.

In addition to monitoring and treatments, growers are asked to prevent spread from human activities, as the pest can be spread by vineyard workers on clothing, tools and equipment moved between infested and non-infested areas, and potentially by movement of plant material and prunings. An investigation is underway by USDA to try to determine how the pest arrived in Napa Valley. As Whitmer says, "It didn't get here on its own."

All the EGVM finds to date are within the territory already under quarantine for the LBAM. "Some of the response and mitigation already in place for the LBAM and preventing its spread has likely helped mitigate the impact of the EGVM," said Nick Condos of CDFA's pest exclusion branch. Quarantine requirements and a compliance agreement will also be developed for the EGVM.

Information sources
• CDFA has a website with information about the pest, at cdfa.ca.gov/PHPPS/egvm/index.html.
• Growers are urged to subscribe to a newsletter to be written, with updates during the season, by Cooper and cooperative extension North Coast IPM advisor Lucia Varela at: cenapa.ucdavis.edu/newsletterfiles/newsletter2084.htm
• Napa County has prepared printed materials in English in Spanish with photos of the different life stages of the EGVM. They are available free for growers and their field employees, including one the size of a business card that vineyard workers can carry in the field. The Napa County Ag Commissioner's office should be contacted to obtain copies and to report EGVM finds at (707) 253-4357, or at co.napa.ca.us/GOV/Departments/DeptDefault.asp?DID=26400. This website will also post EGVM trapping results and updates this season.

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