Destructive grapevine moth has been eradicated in California after seven-year war

After a costly seven-year battle that imposed quarantines and forced vintners to take elaborate steps to protect California’s multi-billion-dollar wine industry, officials have declared victory on the European grapevine moth.

The moth has been eradicated from California and its quarantine restrictions have been lifted, federal and state agricultural officials said this week.

The announcement comes after years of treatment and programs assisted by $65 million in funding from the federal government. Despite the effort, the insect cost California’s wine industry millions of dollars to protect the state’s third most valuable crop.

“This is a very significant accomplishment,” said Tony Linegar, the agricultural commissioner for Sonoma County, where as many as 8,200 traps were placed during the outbreak to monitor the moth’s path. “Any time you propose to eradicate an insect from a continent, that is a very lofty goal.”

At its height, the moth caused notable damage to grape crops across a large swath of the North Coast. The quarantined areas extended from Fresno County to Nevada County. For example, the insect wiped out a vineyard’s chardonnay crop in Oakville in 2009, the first year it was detected in the region. Napa and Sonoma counties have had 446 square miles under quarantine regulation since June 2010, according to Rep. Mike Thompson, D-St. Helena, who helped secure the federal funds.

Growers in quarantine areas were forced to take additional precautions as well, Linegar said, such as placing tarps over bins of freshly picked fruit to be trucked to the crush pad, and washing all equipment before it was removed from a quarantine area.

The moth causes damage as its larvae feeds on grape bud clusters or flowers during the spring bloom. That later leads to fungal infections, most significantly botrytis cinerea.

“Left unchecked and untreated, this infestation would have grown and grown,” said Dave Whitmer, who served as agriculture commissioner for Napa County for 20 years until he retired in 2013.

The infestation peaked in 2010 when more than 100,000 moths were detected through traps in the state, forcing agricultural agencies and the wine industry to resort to a coordinated effort consisting of trapping, the application of insecticide and other practices to prevent its spread, such as taking control of abandoned vineyards, Linegar said.

Whitmer credited a lab-manufactured pheromone that was draped from trellises as a crucial piece that helped eradicate the insect because it confused male moths in their efforts to find females to mate with.

“I would venture we wouldn’t have had the success without the use of the pheromone,” Whitmer said.

The effort produced results, with moth detections dropping to 144 in 2011. The last moth was discovered in Cazadero in 2014.

“It was a pretty major undertaking,” said Rex Stults, government relations director at the Napa Valley Vintners trade group. “I was in meetings where people would roll their eyes and there would be snickering when it was brought up we have a chance for eradication... But it happened.”

Agriculture officials never determined how the moth got into the state, Whitmer said.

Even with the success against the moth, the industry faces other threats, specifically over the outbreak of Pierce’s disease that has forced local growers to pull out and replant thousands of vines.

The glassy-winged and blue-green sharpshooters transmit the disease bacterium into a vine, impeding its water flow and ultimately killing it.

Researchers at UC Davis are attempting to breed a grapevine resistant to the disease.

You can reach Staff Writer Bill Swindell at 521-5223 or bill.swindell@pressdemocrat.com. On Twitter @BillSwindell.