As if late season wet weather weren’t enough to worry about, California and federal agricultural officials have declared a 103-square-mile quarantine in Nevada County after European Grapevine Moths (EGVM) were detected earlier this month in two traps, one in a vineyard in western Nevada County and the other in Nevada City. In late 2009, EGVM found their way to California’s Napa Valley, causing officials to impose a quarantine in parts of Napa, Sonoma, and Solano Counties. Farmers and those who harvest, transport and otherwise process or handle grapes and other crops affected by the EVGM are generally asked to  sign compliance agreements that indicate how crops and any equipment that enters the quarantine area are to be handled and tracked during the quarantine. Several other grape and fruit growing regions have experienced similar quarantines since, including parts of Mendocino, Santa Clara, Fresno, Merced and San Joaquin counties.

EGVM are found throughout Europe as well as in parts of Asia, Japan, North Africa, and South America. It is their larvae, not the adult moths, that cause damage to grapes and other fruit crops. The first generation of larvae emerge in early spring and feed on grape bud clusters or flowers; if they cause significant flower damage, yield will be reduced. Second generation larvae feed on grapes and pupate (undergo metamorphosis) inside the grape clusters. The third generation, which emerge in early fall, cause the most damage by feeding on ripening grapes and exposing them to fungal development and rot.

The California Department of Food and Agriculture (CDFA) recommends flower removal as the best course of treatment for EGVM infestation. If vineyard owners prefer not to remove the flowers, the second choice is treatment with the organic compound known as Bt, or bacillus thuringiensis, a naturally-occurring extract from bacteria that controls the EGVM population. More information on the quarantine and other areas that have been affected by EGVM is available on the CDFA website.


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