Grapevine moth worries farmers in Fresno County, nation’s top grape-growing region

Grape-loving moth invades Calif.’s wine country

SAN FRANCISCO — A moth with a devastating appetite for grapes is causing worries in California’s San Joaquin Valley, the country’s top grape growing region.

The European grapevine moth, unknown to this country until late last year, has found its way to the region’s heart of Fresno County, where grapes are a $725 million-a-year industry and the valley’s top crop.

Three moths were discovered in traps in separate locations in Fresno County over the last week, and local, state and federal agriculture officials have started an aggressive campaign to stop the invader from multiplying.

More than 80 square miles around the area where the moths were found are under quarantine, meaning growers face heavy regulations on how to handle their crops and equipment. Chemical treatment is slated to begin next week.

The good news for the valley’s grape growers is that with more than 5,000 traps set across the county, officials have yet to find more moths. In Napa County, the nation’s storied wine country, 50,000 grapevine moths have been trapped.

“We have a chance of stopping this before it becomes another Napa,” said Les Wright, the deputy commissioner of agriculture for Fresno County.

The moth, about a quarter of an inch in size, is native to Europe, but is also found in southern Asia, North Africa, South America and the Middle East. It was first discovered in the United States in Napa County last fall, when it destroyed the crop of an entire vineyard at peak harvest time before anyone had recognized it as a new invader.

The moth has since traveled to neighboring Sonoma, Solano and Mendocino counties, though the greatest number, by far, have been caught in Napa.

How it made its way to Fresno, 200 miles from Napa, remains a mystery.

San Joaquin Valley farmers are already contending with other pests, including the Mediterranean fruit fly, the light brown apple moth and the Asian citrus psyllid.

The European grapevine moth, while favoring grapes, will also eat its way through a long list of tree fruits, including peaches, plums, nectarines, pomegranates, kiwi and persimmons. It is especially dangerous to grapes because it feeds on them in both the moth and the larvae stage — the larva feed on grape flowers and developing fruit.

Second and third generations of the moth cause the most damage directly by feeding on mature grape berries and indirectly by predisposing the crop to gray mold, a fungal infection.

The moths lay eggs in April and start their first round of feeding at the flowering stage.

The pest would have a feast in Fresno. Though the Napa-Sonoma wine region grows the state’s most expensive grapes, the San Joaquin Valley, and Fresno County in particular, is the nation’s largest producer of grapes, including table grapes, juice grapes and raisins, Wright said.

Fully 80 percent of the raisins consumed around the world come from Fresno, he added.

In Napa, agricultural officials quarantined about 332 square miles across wine country on Wednesday after discovering the moth in at least 32 sites, said Elizabeth Emmett, a county spokeswoman.

Barry Bedwell, president of the California Grape and Tree Fruit League, said that growers are cautiously optimistic that the early detection of the moth in Fresno will mean it can be stopped before most grapes are in season.

Grapes are not harvested until late summer.

“Our confidence level is high that we’ll be able to catch this on the onset,” Bedwell said.

Still, growers in San Joaquin Valley face potentially major headaches and expenses. A quarantine means tarping truckloads of the fruit, washing tractors, mechanical harvesters and fruit bins before transport and submitting to inspections of fields, packing houses and processing plants.

Even the seeds and skins left after grapes are crushed have to be disposed of at a proper facility.

Bedwell, of the California Grape and Tree Fruit League, said that though farmers face hassles, if the grapevine moth infestation grows, it could affect the export trade.

“It’s a huge problem even at the level that we’ve found it,” Wright said. “We’re still working out the details of the boundaries of the quarantine zone and what encompasses the procedure of moving the farm products out of that region. We don’t have all the answers yet. “And we can’t even begin to estimate the costs until we have more answers.”