More than a third of Mendocino County's vineyards are likely to come under quarantine due to the European grapevine moth, and the top agriculture official there wants more growers spraying to kill the pests.

The news comes a day after Sonoma County agriculture officials said they expect half their county's vineyards to be placed under state quarantine because of the insect that has heavily infested nearby Napa County.

About 6,000 acres of Mendocino County vineyards will come under restrictions, said Tony Linegar, the county's agricultural commissioner. "The whole Ukiah Valley will be under quarantine," he said.

The restrictions come after discoveries of the grapevine moth both north and south of Ukiah. Thirty male moths have been confirmed north of the city near Dunnewood Vineyards and Winery, and one has been confirmed in a residential yard to the south near State Street and Highway 253.

Two more insects have been found in the north and two in the south, though the state has yet to confirm them as grapevine moths.

The moths, native to Mediterranean Europe, were first confirmed last September in the Napa Valley, where they destroyed one vineyard's crop and damaged several others. The moth larvae burrow into and feed on the berries, often infecting the fruit with bunch rot.

This year more than 30,000 of the pests have been trapped in Napa County, and small numbers have been found in five other counties, including Sonoma and Mendocino.

About 30,000 acres of Sonoma County vineyards could come under quarantine due to 18 moths found here, county officials said.

Growers in quarantine areas can still move their crops to market, but they must agree to do so in ways that prevent the spread of the moth. Required practices will include washing tractors and other machinery and ensuring that grapes don't spill on the way to wineries.

In Ukiah, moths have been trapped recently on a home grape arbor and on a plum tree in a commercial area, Linegar said.

Experts from the UC Cooperative Extension have recommended that any grower within 1,000 meters of a trapped moth spray to kill eggs and larvae with what they characterize as low impact pesticides, including some approved for organic operations.

But Linegar said the spray zone should be expanded in order to ensure that the moth is eradicated in Mendocino County this season. He said he may ask all growers in the Ukiah Valley to voluntarily spray for the insect.

Devon Jones, executive director, of the Mendocino County Farm Bureau, called the news of the expanded quarantine area a cause for concern.

"We're trying not to overreact," Jones said. "At the same time, we're taking it pretty seriously."