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."
Along with chemical treatments, growers in quarantine areas must comply with new rules to prevent the spread of the moths. That includes washing tractors and other equipment before exiting infested vineyards.
Growers also must prevent grape spills during shipment. For many, that means leaving at least four inches of room at the top of the bins that carry grapes from the fields.
"It's our new standard operating procedure," said Jon Ruel, vice president of Napa Valley Grapegrowers. "We're not filling the bins as much."
Growers also can completely fill the bins if they place tarps over them.
Along with Napa, the counties with existing quarantine areas are Sonoma, Mendocino, Lake, Solano, Santa Clara, San Joaquin, Merced and Fresno. As well, moths have been found but haven't yet triggered quarantines in Santa Cruz and Monterey counties, said Larry Hawkins, a spokesman for the USDA.
No moth has been found in Lake County, but a portion of land came under quarantine due to its proximity to traps that caught the pest in nearby Napa. Lake County Agricultural Commissioner Steve Hajek has asked the federal government to change the county's status because it could prevent the shipment of Lake grapes to other countries.
"We should not be in this quarantine," Hajek said. He said the Napa moths can't reach Lake because of an 1,100-foot mountain that lies between the two counties.
To fight the moth, Sonoma County has hired 12 trappers and nine biologists on a seasonal basis to seek the pest in the fields and at wineries, said Agricultural Commissioner Cathy Neville.