2010 Annual Report

Adult European grapevine moth. Photo by J. K. Clark

Advisors tackle European grapevine moth

UC Cooperative Extension viticulture and IPM advisors are engaged in an all-out effort to combat the European grapevine moth (EGVM), first trapped in Napa County in September 2009 and since trapped in eight other California counties.

The insect had never before been caught in the United States, but it is the primary pest on grapevines in Europe and can be expected to cause significant economic harm to California’s diverse grape industries if it becomes established.

The UCCE advisors’ work contributed to a dramatic reduction in 2010 of EGVM populations in Napa Valley from about 100,000 moths caught in the first generation to about only 1,000 moths in the second. Napa County was by far the hardest hit; by comparison, the number of moths caught in counties that surround Napa and in the Central Valley was very low for all three generations in 2010.

By applying reduced-risk chemicals for this new pest, growers in quarantined areas preserved their ongoing vineyard IPM programs and protected important natural enemies that keep several other grapevine pests under control.

Throughout the 2010 growing season, Viticulture Advisor Monica Cooper monitored EGVM pheromone traps and the vineyards where they were placed. Twice a week she distributed a newsletter telling growers and pest control consultants what she was seeing in the traps and vineyards.

From her observations, Cooper and UC IPM Advisor Lucia Varela advised growers in quarantine counties about the best time to spray for each of three EGVM generations. These treatments of reduced-risk insecticides were combined with voluntary use of mating disruption in about 12,000 acres in the Napa Valley. In addition to Napa County, this pest has been trapped in Fresno, Lake, Mendocino, Merced, San Joaquin, Santa Clara, Solano, and Sonoma counties.

Getting the word out about EGVM was critical to its control. Cooper, Varela, and other UCCE advisors including Rhonda Smith from Sonoma County, Larry Bettiga from Monterey County, Steve Vasquez from Fresno County, and Walt Bentley in the Central Valley gave myriad presentations to growers and consultants throughout 2010, and they prepared many articles for trade magazines and for posting on the Web.

In addition, UC IPM has partnered with USDA’s Natural Resources Conservation Service to develop a complete set of outreach materials about EGVM for the upcoming field and meeting seasons. The materials include:

• Presentations in Spanish and English for viewing on the Web;
• Posters in Spanish and English to show field workers what to look for;
• A handout about EGVM to help consultants and supervisors recognize and monitor for it; and
• A handout to help consultants and supervisors distinguish EGVM from the several other similar larvae they might find in a vineyard.

Varela originally worried that EGVM would be as difficult to control as codling moth in pears or apples.

“When first generation codling moths bore into these fruit, it’s all over before you even get started,” she said. 

Varela attributes the dramatic decrease in the Napa County EGVM population to well-timed treatments of the first and second generations.

“Control of the first generation is easy, because the larvae are exposed in the flower clusters and you can get good spray coverage,” she said. “Early in the second generation, the larvae are still on the outside of the fruit, and it’s not difficult to get the spray to them then either. You’re home free as long as you’ve controlled EGVM before the third generation; since those larvae bore into the fruit, the spray doesn’t reach them.

“The long residual and egg-killing actions of a few newer, reduced-risk insecticides used by growers to control EGVM gives them an advantage over conventional organophosphates and pyrethroids,” Varela added. “They not only last longer, but these pesticides also are easy on the natural enemies that keep mealybug—believed to move leafroll virus among vines—in check.”

Organic growers controlling EGVM have been able to continue their organic status through use of approved products too. They effectively used Bacillus thuringiensis or an organic formulation of spinosad to control EGVM. While they had to spray more often than conventional growers who applied insecticides with longer residue, the organic growers still were able to control populations without any damage.

In conventional vineyards, growers can apply first and second generation EGVM sprays along with the standard spray for powdery mildew.

Dispensers of the Isomate EGVM pheromone are available for mating disruption. Isomate EGVM was applied to both conventional and organic vineyards in the core-infested area in Napa County.

The research team also conducted several studies related to monitoring and managing this new pest.

• Varela used Cooper’s trap and monitoring observations to validate degree-day phenology models from France, Italy, and Spain that relate events in the EGVM life cycle to temperature. Initial results show that the French model, most commonly used in other parts of the world that already have EGVM, tracked EGVM biology most closely during the 2010 season.
• The team tested conventional, organic, and reduced-risk insecticides against the moth, learning that the reduced-risk chemical methoxyfenozide (Intrepid) did the best job on small larvae.
• They also tested the effectiveness of commercially available lures. Both rubber septa and membrane lures proved effective and lasted as long as advertised by the manufacturers.
• Smith, Cooper, and Varela are studying the survival of EGVM larvae after grapes are pressed or de-stemmed and crushed.

The dramatic reduction of EGVM populations is encouraging, but no one is yet predicting whether next season’s populations will be big or small or where EGVM will be found. Informed growers and consultants will need to stay vigilant to find EGVM and respond quickly.

Scientists will need to provide better tools for monitoring and controlling EGVM. An important task is to finish validating the EGVM degree-day model so that it can be used to accurately time insecticide sprays and reduce the number needed. Also, as mating disruption is used in more of the infested area, new tools will need to be developed to monitor populations, since the current pheromone lures used in traps will become less effective as pheromones from dispensers compete with them.

For more information, see EGVM on the UC IPM web site.

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