Napa County grape growers are gearing up to battle a new exotic moth this spring, even as state and federal officials plan to investigate whether the invasive pest has spread elsewhere in California.

The search for the European grapevine moth includes Sonoma County, where traps will be set. Local growers already are watching the eradication efforts in nearby Napa.

Agriculture officials this spring plan to assess the extent of the moth's invasion and to use organic and what they call low-impact pesticides where they find infestations.

"We don't have a clear picture of what it is that we're dealing with," Assistant Napa County Agricultural Commissioner Greg Clark said this week. A trapping program will answer that question both in Napa and around the state.

The moth, a native of Mediterranean Europe, showed up last September in an Oakville vineyard. It ruined the crop by attacking the berries and infecting them with botrytis, also known as bunch rot.

It was the first time the pest had been found in the United States. The pest is a threat to California's table grape and raisin crops, as well as to its wine grapes, officials said.

Since then the pest has been discovered on about 30 properties. Most of those sites lie between Yountville and St. Helena, Clark said, but the moth also has been found east of Napa.

Congress has allocated $332,000 for a moth trapping program throughout California, said Larry Hawkins, a spokesman with the U.S. Department of Agriculture.

A statewide survey would prove valuable, Hawkins said, because "it tells you where the insect is. But just as importantly, it tells you where it isn't."

Most of the suspected infestation area in Napa already is under quarantine for another foreign pest, the light brown apple moth.

Agriculture officials in the county met last week to discuss eradication efforts with about 150 growers and other industry members, Clark said. As well, the 550-member Napa Valley Grapegrowers will discuss fighting the pest in a March educational forum.

Three generations of the moth live during a typical growing season. The third generation often does the most damage to the grapes, but officials hope to attack the first two generations in order to prevent later crop loss.

Jon Ruel, chairman of the grape growers' industry issues committee, said organic and less-toxic pesticides can kill the pests when they emerge as larvae, possibly in March.

"Knowing the bug has a vulnerable life stage gives us a bit of hope," said Ruel, director of viticulture and winemaking at Trefethen Family Vineyards.

In Sonoma County, traps were set out late last year. Nothing turned up, but that finding isn't definitive because by then most of the pests would have been in the pupae life stage, not alive as moths, and would have been able to survive the winter inside silken cocoons.

Sonoma County officials plan to set new traps this spring. Sonoma County Agricultural Commissioner Cathy Neville said farm officials take seriously the moth's ability to inflict damage on grape crops.

"This one is the real deal," Neville said.

Nick Frey, president of the Sonoma County Wine Grape Commission, said growers think it likely that the moth will be found in more than one California county.

"It's hard to believe that it's only in Napa," said Frey.