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Winegrowers Start Spraying New Pest

Advisors urge action in California vineyards now to control destructive European grapevine moth

by Paul Franson
European Grapevine Moth
Photo by Jack Kelly Clark/University of California
Napa, Calif. -- With the disclosure that eggs of the dreaded European grapevine moth (Lobesia botrana) are hatching into larvae in Napa Valley, California winegrowers have started spraying pesticides -- both organic and conventional -- to counteract the invasive pest, which can destroy grapes. The insects have now been found in Sonoma, Mendocino, Solano and Fresno counties.

Dave Whitmer, Napa County’s agricultural commissioner, and Dr. Monica L. Cooper, the viticulture farm advisor and Napa County director of the University of California Cooperative Extension, are at ground zero of the invasion, which first came to light in Napa County last fall

Cooper warns, “Timing of treatment is based on life stage. Organic insecticides will not kill eggs, so (they) should be applied to young larvae. Most of the conventional insecticides are larvicidal, although some also have ovicidal activity.”

And while Whitmer is charged with enforcing ag rules to protect crops, he’s considered an enlightened advisor to the industry and works closely with Cooper, her colleagues and growers. He says that eggs are hatching while older adults already have been observed flying. They emerged from their pupae in mid-February.

Cooper is evaluating the development of the eggs. “They go through a stage just before emerging called the black head or black cap stage,” Whitmer says.

Whitmer’s office has notified growers whose vineyards are already infested or within 200 meters of traps where the pests have been caught. He says, “We’re asking them to treat their plots with insecticide.”

Evaluating the pesticides

Many facets come into play with pesticide application. For one thing, many vineyards in Napa County and elsewhere are farmed organically or certified organic; most growers minimize their use of chemicals in any case.

Also, Whitmer points out that leafroll virus is a big issue in the area, and it can be spread by mealybugs. Pesticides can disrupt the biological controls for mealybugs, which have been working well.

Working with Dr. Lucia G. Varela of the UC Cooperative Extension and Statewide IPM (Integrated Pest Control) Program, Cooper has investigated the insecticides, and a PDF detailing their findings can be downloaded here .

Intrepid is the most widely used pesticide. It kills eggs and larvae and has low toxicity to beneficial predators, parasitoids and bees. It’s not approved for organic vineyards, however. Entrust, which is approved for organic growing, is not effective against eggs, and it is also medium- to highly toxic to beneficial parasitoids and bees.

Whitmer’s office also is using pheromones to attract the European moths to traps, but Whitmer encourages growers to place disruptive lures at least 30 meters away from the county traps, so as not to disrupt monitoring. The lures confuse male moths hunting for females; guidelines are being developed to use these lures more widely. “This sustainable technique is used in Europe successfully,” according to Whitmer.

Rhonda Smith, Cooper’s counterpart in Sonoma, says the ag commissioner there notifies growers if a moth is found in a trap within 1,000 meters. “If so, the vineyards are likely infested,” Smith says.

She says that some growers are starting to spray immediately, but others are setting out their own traps, which are available from farm supply dealers. “If they do find bugs on your property, it’s definitely infested, and they tell you to spray. You can monitor the clusters for signs of worms. This is the perfect time to do spray,” according to Smith. She recommends that all growers in Sonoma set out traps.

With news last week that the moth has now been found in Fresno County, Whitmer suggests it is being spread by moving equipment or materials -- the moth doesn’t have a long range. It’s especially important to clean equipment.

Napa and Sonoma already are under quarantine, although the details haven’t yet been announced. This quarantine is sure to be in effect during harvest, and growers and wineries are awaiting news of how they’ll be affected.

Also worrisome are abandoned vineyards and backyard vines in cities and elsewhere. Homeowners may be asked to consent to spraying or destroy flowers and fruit. That’s bound to raise concerns among members of the population who are already worried about chemicals in the environment.

The affected area also is home to native wild grapes in riparian areas, a concern of Napa ag commissioner Whitmer, whose office is formulating plans to deal with the invasion.

Cooper has posted extensive information about the bug and fighting it to
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