The European grapevine moth is a serious threat to Sonoma County's trademark crop.

A quarantine that extends into Sonoma County took effect last month, triggered by the discovery of the pest in vineyards near St. Helena and Napa. Last week, as a trapping program expanded across California, a single grapevine moth turned up in an agricultural area near Kenwood.

A native of Italy, the grapevine moth has caused crop damage in Europe, Africa, Asia and the Middle East. It hadn't been found in the United States before September. An infestation in California would be costly.

As state Food and Agriculture Secretary A.G. Kawamura noted when he imposed a quarantine on 162 square miles of Sonoma, Napa and Solano counties, "Grapes are our state's top crop." The state's crop was valued at $2.74 billion in 2009, with the North Coast accounting for about $1 billion of that figure.

As much as a third of Sonoma County's vineyard land already is under quarantine due to another pest — the light brown apple moth. Growers also remain concerned about the glassy-winged sharpshooter. Because the European grapevine moth produces three generations in a growing season and feeds on grape flowers and young fruit, it poses an especially serious threat.

While the discovery of a single grapevine moth won't trigger a quarantine on Sonoma Valley grapes, it isn't too soon to prepare an eradication plan.

"I think the question is how manageable will this pest be, and can we get ahead of the curve in managing it so that it doesn't have severe economic ramifications," said Lex McCorvey of the Sonoma County Farm Bureau.

In the quarantine area, some growers are using pesticides, and state, federal and local officials plan to use twist-ties containing the pheromones of female moths to confuse males and disrupt the mating cycle.

Twist-ties, which are commonly used in organic farming, were the preferred approach to battling the light brown apple moth. But the program was delayed by speculation and unsubstantiated fears about the ties (which are also known as pheromone ropes), and federal agriculture officials concluded last month the apple moth can no longer be eradicated.

However, agricultural officials still plan to control the apple moth population with the twist-ties. If that approach also proves effective with European grapevine moths in the quarantine zone, it shouldn't be excluded from an eradication plan for Sonoma County.