Napa County’s efforts to contain the European grapevine moth (EGVM) have produced dramatic results.
The 4,000 pheromone traps (one per 20 acres) in the county are unfolding a story of success thus far in bringing the EGVM under control.
“At the end of last season there were vineyards with really bad EGVM infestations, says Martin Mochizuki, Napa County’s EGVM grower advisor. “We were seeing almost one larva per berry.”
This year, about 99,000 moths were trapped in the first generation. “During sunset, at the peak of the first flight, you could see the moths swarming like mosquitoes,” he says.
Following an aggressive first generation treatment effort by growers in the infested area, only 1,300 moths were trapped in the second generation. By the third generation, the trap count had dwindled to only about 100. No grape damage was reported from the second EGVM generation, Mochizuki notes. So far, he has heard of only one vineyard being damaged by third generation larvae.
“Everyone is pleased at this amazing reduction in the EGVM population,” he says. “It reflects the cooperation of all the growers.”
The discovery last September of EGVM near Oakville was the first find of the grape-eating pest in the U.S. A grower in the area of the original Napa County EGVM finds lost his entire crop to the pest.
This sent shockwaves through California’s grape growing areas, and federal and state regulators blanketed the state with traps to see where the pest had spread. Finds in seven California counties prompted quarantines that covered almost 2,000 square miles in seven counties: Fresno, Mendocino, Merced, Napa, San Joaquin, Solano and Sonoma.
In Napa County this year, the flight of the third and most damaging generation of EGVM ends this month. It’s also expected to be the last flight of the year.
For the first two generations, conventional and organic growers in the county dramatically reduced EGVM numbers by treating vineyards with synthetic insecticides and organically approved materials, tank mixed with powdery mildew control sprays. Conventional growers sprayed the first generation of EVGM twice and the second generation once, says Mochizuki. Organic growers sprayed each of the first two generations three times. The third generation was treated in mid-August.
The treated vineyards include those in the core treatment area of about 12,000 acres that were heavily infested with the EGVM last year. This represents about 150 growers.
A treatment area is comprised of vineyards within 200 meters of a known moth find, while the quarantine area covers any vineyard within a five-mile radius of a find. In this case, the quarantine encompasses all of Napa County.
Growers also used pheromone dispensers in a mating confusion strategy, which became available just before the second EGVM flight. The product, Isomate, was placed in vineyards at a rate of 200 dispensers per acre, Mochizuki says. Next year, he expects growers will put them out just before bud break.
He estimates material costs for the EGVM sprays this season totaled about $150 per acre for conventional insecticides and $250 per acre for organic products. Buying and placing the pheromone traps cost about $100 per acre.
In November, USDA and California Department of Food and Agriculture officials will meet with EGVM experts from around the world to assess the containment effort in California and map out a strategy for 2011 that, hopefully, will eradicate EGVM.