Pesticide treatments and new rules for transporting wine grapes have struck a significant blow against the European grapevine moth this season, keeping it from spreading in the North Bay and vicinity, farm officials said.
More than 100,000 moths were trapped earlier this year in Napa County, according to the U.S. Department of Agriculture. But the numbers there have dropped from 66,000 moths trapped in April to only 113 taken in August.
Fewer than 120 such moths have been found in 10 other counties around California where the pest has been confirmed. That includes 58 moths found in Sonoma County and about three dozen in Mendocino County.
A few moths recently have been trapped in Santa Clara and Santa Cruz counties, and the battle against the pest is far from over. Even so, officials expressed hope that pesticides and the transport rules can keep the moths in check, and possibly even eradicate them from many areas.
"We've identified good, economical strategies for controlling this pest," said Jim Allan, agricultural commissioner for Solano County.
The moths, native to Mediterranean Europe, were first confirmed a year ago 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.
Officials said scientists have concluded that the moths can't fly great distances and instead have hitchhiked to new areas in grape shipments or on farm equipment during past harvests.
This year, Napa growers responded to the pests with what advisers from the UC Cooperative Extension have described as low-impact pesticides, including some approved for organic operations. In Sonoma and Mendocino counties, growers used the same pesticides when within 1,000 meters of a trapped moth.
The pesticides have proven effective against the moth larvae.
"The pest is very soft," said Mendocino County Agricultural Commissioner Tony Linegar. "It's easy to kill."