California and federal agricultural officials have declared a 103-square-mile quarantine 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 the Nevada City area.

Officials have met with growers and begun notifying related businesses in the affected area, working with them to complete compliance agreements that determine how crops, plants, harvesting equipment, and other items must be handled to prevent the spread of the pest.

“Quarantines are a necessary step in controlling and eradicating pest infestations,” said Karen Ross, Secretary of the California Department of Food and Agriculture. “These regulations allow us to protect surrounding areas by preventing movement of the insects on crops, harvesting equipment and related articles.”

A map of the quarantine area is available online at: http://www.cdfa.ca.gov/phpps/PE/InteriorExclusion/egvm_quarantine.html(scroll down to the heading “Quarantine Maps.”)

The pest was first detected in California in late 2009 in Napa County, leading to a quarantine covering portions of Napa, Sonoma and Solano counties. Smaller quarantines have since been declared following detections of more isolated infestations in Mendocino, Santa Clara, Fresno, Merced and San Joaquin counties. The quarantines cover approximately 2,000 square miles.

The quarantines primarily affect farmers as well as those who harvest, transport and otherwise process or handle grapes and other crops. These growers and business people generally sign compliance agreements that indicate how crops, vehicles, equipment, and related articles are to be handled and tracked during the quarantine.

Residents are also affected by the quarantine. Those who have grapes, stone fruit trees (peaches, plums, etc.) and other host plants for this pest in their yards are asked to harvest and consume their fruit on-site to further limit the risk of spreading the pest.

Residents who have questions about the pest or the quarantine are encouraged to call CDFA’s Pest Hotline at 1-800-491-1899.

CDFA’s first choice for treatment to eradicate EGVM infestations is removal of the flowers and fruit from grapevines. If property owners would prefer otherwise, the second choice would be treatment with the organic compound Bt, or bacillus thuringiensis, a naturally-occurring extract from bacteria. Either option will control EGVM on the properties and greatly reduce the risk of spread to commercial vineyards. 

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

The EGVM 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 in the clusters or in leaves. 

Larvae of the third generation - the most damaging - feed on multiple ripening grapes and expose them to further damage from fungal development and rot. These larvae overwinter as pupae in protected areas such as under bark, and emerge as adults the following spring.