Napa issues urgent warning after invasive pest found on grapevines sold at Costco

NAPA, Calif. -- An urgent alert was sent Tuesday morning from Napa County's agricultural commissioner regarding an infestation of the glassy-winged sharpshooter insect on grapevines sold at Costco Wholesale and found in shipments across Napa, Sonoma, Marin, Solano and Yolo counties.

Glassy-winged sharpshooters, with an appearance similar to crickets, can cause Pierce's disease, a bacterial infection that blocks water-conducting systems in plants, drying them out. The disease is incurable.

A total of 220 grapevines shipped from Burchell Nursery in Fresno County between April 21 and Tuesday were delivered to Costco Wholesale in Napa. According to a statement from Tracy Cleveland, Napa County's agriculture commissioner, "63 of the 220 grapevines delivered to Napa Costco have been destroyed and one GWSS egg mass was found."

However, the remaining 157 grapevines "may be in the possession of community members who purchased them at Napa Costco," says the statement.

In May, grapevines are blooming along with small grapes, but on infected vines, growth will be diminished. "Scorched" leaves will not appear until the end of summer.

"I'm really worried, but unfortunately it's a matter of time before we know what happens," said Chris D'Alo, a viticulturist with Nord Vineyard Services in Napa who also manages vine health. Typically, he said, county workers use pheromone traps to catch adult sharpshooters.

"There's still a chance to claw those vines back and make sure there won't be a spread. As an organized effort, it's going to cost money."

"It will take years before it's really obvious. But we know it will be bad," said D'Alo.

If the glassy-winged sharpshooter were introduced, "they would be difficult and costly to eradicate, and the increased losses from Pierce's disease could devastate the local vineyard, winery and tourism industries," reads a page dedicated to the pest on the county's website.

A 2008 study from the University of California found that between 1994 and 2000, Pierce's disease caused nearly $30 million in losses and destroyed over 1,000 acres of grapevines in Northern California.

"I am confident that the community will pull together to help us limit the risk to our local agriculture. Vigilance and prompt reporting are essential," read Cleveland's statement.

Costco is directly contacting members who purchased plants between April 21 and Tuesday and has been a cooperative partner with all county ag commissioners.