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An acre of vineyard in Napa County can produce between three and four tons of quality grapes.
When a voracious pest triggered a quarantine this week across much of Napa Valley -- the nation's premier grape-growing region -- it threatened more than the grapes themselves.
The spraying of pesticides needed to control the European grapevine moth threatens to undo decades of low-impact farming practices that have elevated the quality of wines from the region. Growers of premium wine grapes have long believed that elegant flavors are tied to the soil.
Agriculture officials imposed a quarantine Tuesday restricting the transport of equipment, grapes and even the skins that are left when they are pressed after discovering the pest in at least 32 sites across Napa Valley.
The moth was first detected in the U.S. last September in a vineyard in the center of Napa Valley. The bug managed to destroy the crop of an entire vineyard at peak harvest time before anyone recognized the new invader. Most growers in the region try to use minimal chemicals on the vines to protect the environment and the flavor of the grapes.
At an average $3,414 a ton for premium cabernet, damage can add up quickly in a county where the crop is worth $400 million annually. One acre can produce between three and four tons of quality grapes.
The moth is the latest stroke of bad luck for the 400 or so Napa Valley vintners who already are suffering from a 15 percent decline in sales of ultra-premium wines and a resulting jump in winery and vineyard foreclosures this year and last. At the least, the presence of the moth will increase costs at a time when many are trying to cut expenses.
Premium grape growers are now facing the prospect of spraying at least three times in the months ahead to deal with the three generations of grape-eating larvae that are produced each growing season. The spraying could cost at least $200 an acre.
The European grapevine moth arrived a decade behind the glassy-winged sharpshooter, a potential carrier of Pierce's Disease. The sharpshooter wiped out 1,000 acres of vines in Temecula in Southern California.
After years of study, authorities now believe the sharpshooter fares poorly in Northern California's cooler climates. The small, brown grapevine moth is native to Europe, but is also found in southern Asia, North Africa, South America and other areas.
Grapes are its main target, but it feeds on other California crops and plants such as kiwi, blackberries and persimmons.The moths lay eggs in April and start their first round of feeding at the flowering stage.
Traps have detected it at sites across the Napa Valley, prompting the quarantine that also stretches into parts of neighboring Sonoma and Solano counties.