This month, Napa County vintners began spraying their vineyards with pesticides in an attempt to fight infestation of European grapevine moths.

The half inch insect lays eggs in April, and the larvae starts feeding at bud break on grape flowers, then later generations on young grapes, and a third generation on mature grapes.

Since September 2009, after destroying a nine acre Napa Valley vineyard’s crop, when the culprit moth was identified, nearly 30,000 moths have been trapped in the county, and plans are being made to quarantine over 300 square miles of Napa County.

Although the moth is not a long distance flier, it does seem able to ride on equipment from vineyard to vineyard, vineyard to winery, and winery to winery. Neighboring Sonoma County is gearing up to institute quarantine protocols to help control moth movement.

Mendocino County, known for environmentally friendly farming practices, sustainable and fish friendly agriculture, organic and biodynamic grape growers and wineries, is facing a quarantine of nearly 6,000 vineyard acres after first one moth was found just south of Ukiah on a back yard grape vine, then more recently another 30 have been found north of Ukiah.

Tony Linegar, Mendocino County Agricultural Commissioner, suspected the moths were transported from Napa when fruit was moved from Napa County to a winery near Dunnewood’s now infested Chardonnay vineyard. Roughly 650 traps are being set in Mendocino County. Linegar believes this may be the second year the moths have been in Mendocino County, and the worst may be yet to come.

Mendocino County wineries use pomace, the residue of pressed grapes, for natural fertilizer. Alarmingly, the European grapevine moth larvae, left inside the grapes, can sometimes survive pressing and end up in pomace. Several Mendocino County wineries regularly import Napa and Sonoma County winery pomace. The problem could very well have been laid right at the feet of the vines already.

Linegar is asking all vineyards within a kilometer of Dunnewood’s infested vineyard to spray with a larvicide.

Purportedly organic insecticides do exist, and are hoped to be effective.

Only 3 of 18 Insecticides for Lobesia botrana (European Grape Vine Moth) on grape are approved for use in organic vineyards. I found no information on approved insecticide use in biodynamic vineyards.

Bruce Phillips, a Napa Valley grape grower, worries about “the long term sustainability of organic and biodynamic practices,” in the face of forced spraying to combat the spread of, or damage from, the moth.

Mendocino County bills itself as “America’s Greenest Wine Region,” and the threat posed by the European grapevine moth is not just to the grape crops but to an entire way of growing grapes.

The County of Napa Agricultual Commissioner’s website states, “Studies of the European grapevine moth internationally show that larvae feed primarily on the flowers and fruit of the grape, and that they can also feed on number of other hosts, including olives, blackberries, cherries, nectarines, persimmons and pomegranates. “

There is further concern that after grape harvest, moths may spend the winter cacooned in olive trees on vineyard properties.

Jim Allen, the Solano County Agricultural Commissioner, describes the threat posed by the moth as having “a potential for complete crop loss.”

A Final Report of  an International Technical Working Group brought together to fight the European Grape Vine Moth in California’s north coast, dated February 10, 2010, recommends that suppression measures include ovicides, larvicides, mating disruption, and mechanical control measures. Three generations of the pest impact vineyards; the first from bud break to fruit set, the second from pea sized grapes to ripening, and the third from ripening to harvest. Whether there are any beneficial organisms that might prey on, or control, the moth is unknown at this point.

The second and third generations cause the most damage not just by direct feeding on mature grapes but by predisposing the crop to grey mold, fungus, and rot through webbing and leaving of excrement inside the grapes.

Since their discovery in Napa County; in addition to Sonoma and Mendocino Counties, the moth has been found in Merced, Fresno, and Solano Counties.