In response to the recent detection of the European grapevine moth (EGVM) in Napa County, the California Department of Food and Agriculture (CDFA) has established a quarantine of 162 square miles including portions of Napa, Sonoma, and Solano counties.

The detection of an EGVM larva in a trap in the Oakville area on Sept. 15, 2009, was the first detection of the pest in the United States.

Confirmation of the detection led to increased trapping and surveys that have since detected the pest at several sites, generally contained in two pockets of infestation: one on the eastern side of the City of Napa and the other between Oakville, Rutherford, and St. Helena.

Maps of the two quarantine zones and additional information are available at www.cdfa.ca.gov/PHPPS/PE/InteriorExclusion/egvm_quarantine.html.

“Grapes are our state’s top crop,” said CDFA Secretary A.G. Kawamura. “This quarantine will help us ensure that the infestation doesn’t have an opportunity to spread.”

“I fully understand that quarantines impact both the public and our growers,” Kawamura said. “It is important and necessary to protect our food supply and the larger environment from these invasive pests so the entire community’s cooperation is essential and appreciated.”

EVGM, or Lobesia botrana, is found in southern Asia, Europe, North Africa, Anatolia, the Caucasus, and in South America. The pest primarily damages grapes, but has also been known to feed on other crops and plants.

Inspectors are working with growers, nurseries, landscapers, and others who work with plants and fruit to guard against spread of the pest by regulating the harvest, shipping, and handling of affected crops and plants.

CDFA and local officials will plan grower meetings to help the agricultural community understand the quarantine regulations.

The EVGM larvae, not the adult moths, are responsible for the damage to grapes. Larvae that emerge early in the spring feed on grape bud clusters or flowers, and spin webbing around them before pupating inside the web or under a rolled leaf.

If heavy flower damage occurs during this first generation, the affected flowers will fail to develop and yield will be reduced. Second-generation larvae enter the grapes to feed before pupating inside the grape.

Larvae of the third generation – the most damaging – feed on multiple ripening grapes causing exposure to further damage from fungal development and rot.

In the Oakville area of Napa County, where the original infestation was detected last fall, one grape grower lost their entire harvest.

CDFA, working closely with the U.S. Department of Agriculture and county agricultural commissioners, has begun an intensive statewide trapping effort to determine whether the moth has infested other areas of California.

In addition to traps already deployed in Napa and the immediate area, traps are being deployed beginning in the warmer, southern region of the state, and progressing northward as the spring weather arrives, grapevines come out of dormancy, and the moths emerge if present.