Pest Control Advice for Napa Grapegrowers

Workshop covers sustainable methods to battle European grapevine moths, mealybugs and other vineyard pests

by Paul Franson
European grape vine moth
The enclosed area of northern Napa Valley has been quarantined to contain the European grape vine moth.

Napa, Calif. -- In fortuitous planning, the Napa Valley Grapegrowers had scheduled a sustainability workshop for a detailed look at pests -- especially the new threat of the European grape vine moth -- that happened to take place just days after the federal government clamped a quarantine on prime Napa Valley growing areas.

With equally opportune timing, Napa County agricultural commissioner Dave Whitmer was able to announce during the workshop that the California Department of Food and Agriculture (CDFA) had in record time approved use of mating disruption traps to combat the moths. The U.S. Department of Agriculture already had approved the use of the traps and their pheromone baits.

Whitmer Kawamura
Napa Agriculture commissioner Dave Whitmer and California agriculture secretary A.G. Kawamura addressed the meeting.

Whitmer was able to make the announcement just after CDFA secretary A.G. Kawamura addressed the group.

The sold-out event found more than 125 growers listening to a daylong litany of pest and disease problems that face them and the latest expert recommendations for dealing with them.

Along with the European grape vine moth, the workshop devoted considerable attention to detecting and fighting the vine mealybug, the current major scourge, and the light brown apple moth; viruses and other diseases that cause leafroll; powdery mildew; botrytis and canker disease.

Almost absent from discussion was the glassy-winged sharpshooter and Pierce’s disease, the main threats just a few years ago. They seem to have been largely contained through aggressive quarantines and other action.

Rhonda Smith, the Sonoma County viticultural advisor, presented a detailed look at the vine mealybug, including monitoring for the tiny pest and control measures. Mating disruption and biological control using predators are being undertaken; soft pesticides require careful timing and application.

Isolation of the pests and sanitation to prevent spreading seem key points, including washing equipment with pressure water (no need for heat or chemicals). People can also carry the bugs on their clothing.

Surprisingly, the mealybugs can survive pressing, so winery waste can be a source of infestation. They can’t survive the heat of true composting, however.

Pete Opatz of Silverado Premium Properties described the efforts the company has undertaken among its many properties, including isolating problems and soaking the plants with pesticides including Venon and orange oil-based products. He admitted, however, “This would be very expensive on a broad scale, but it’s effective if you only have to treat a limited area.”

European grape vine moth
Unlike many vineyard pests, the European grape vine moth destroys berries from the inside. Photo by Jack Kelly Clark/University of California

Perhaps the talk of greatest interest was that of Dr. Lucia Varela about moths, particularly the European grapevine moth (Lobesia botrana). Large areas east and north of Napa had just been quarantined after the first finding of the pest in America.

All areas within three miles of a moth found in a trap are quarantined, but initial rumors that grapes couldn’t be taken from their sites aren’t true. Whitmer assured growers that they will be able to transport fruit to wineries, but will have to get permits and assure regulators that they’re taking steps to prevent spread of the moths.

Perhaps the biggest concern about this pest is that it is a berry moth that gets into the berries and destroys them, which could obviously affect wine quality. Other moths and leafhoppers reduce yields and can damage vines, but they don’t inhabit the grapes.

State, federal and county authorities are trying to get a handle on the extent of the problem. Whitmer says the county has installed 750 traps in areas known to be infested, and the state has put 2,200 to 2,500 traps in other parts of the county.

They can be controlled by many insecticides including bacillus thuringiensis, but as Dr. Varela says, “We don’t want to load up the environment with pesticides that will develop resistance and kill natural predators.”

The moth has natural enemies in Europe, too, but the immediate effort is to use mating disruption with traps from Pacific Biocontrol. These twist ties must be installed at 200 per acre over a significant area (10 acres minimum).

Dr. Deborah Golino, director of the Foundation Plant Service at the University of California, Davis, discussed leafroll and why it’s become a bigger issue lately. “We have a serious problem in the North Coast due to leafroll virus,” she said.

The cure, she stressed, is clean vines. She was happy to talk about her new 100-acre Russell Ranch near Winters, which will be the site a new federally funded National Foundation Vineyard collection of vines that have been through microtip culture to remove viruses. She also announced a new test, the TaqMan real-time assay, which can positively identify which of the numerous viruses are causing leafroll. An equivalent project will be developed on Long Island, N.Y., by Cornell University.

Dan Martinez, who owns Martinez Orchards, explained the changes coming to help ensure clean vines, both rootstock and scions. He also noted that almond growers, who sell about $3 billion in crop yearly, assess themselves at $45 million for plant research; winegrape growers, who sell $2.1 billion, only contribute $3.6 million annually.

European grape vine moth
Another area of the southern valley has also been quarantined.

The day’s last educational session was a description of fungus problems and how to deal with them. Secretary Kawamura followed with a recollection of his experience with winegrapes and wine, as well as other farming.

The workshop began with a talk by Hal Huffsmith, vice president of vineyard operations for Trinchero Family Estates, who oversees 6,500 acres of vineyards including about 225 in Napa Valley. He pointed out that a prime reason the pests spread so rapidly in the area is its monoculture of grapes -- something that’s not likely to change much, though ag commissioner Whitmer has called a meeting next month to discuss diversifying farming in the valley once more.

Huffsmith called for increased use of science, including investigating other choices such as different varieties, vines developed by classic breeding and even genetically modified vines. He also urged heeding farmer wisdom and increased cooperation among growers and agencies. “If we don’t cooperate, we will have serious problems,” he warned.

With a new pest appearing every few years, perhaps the best advice of the day was Dr. Lucia Varela’s warning -- “assume you have everything” -- and act accordingly. Fortunately, as grower Larry Hyde noted, “The treatment for all of them seems to be the same.” That’s detection and monitoring, isolation, sanitation and treatment.

The Napa Valley Grapegrowers have regular educational events; the next is April 12, “Ahead of the Curve.” Learn more at napagrowers.org.

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