photo credit: Tina Caputo
Napa County ag commissioner shows a picture of a glassy-winged sharpshooter.

Northern California’s agriculture community is on high alert after glassy-winged sharpshooter insects were found on grapevines sold at Costco stores in 24 counties.

As a vector of Pierce’s disease, the leafhopper is a threat to the region’s vineyards. And once a vine is infected, there is no cure.

“Once a vineyard gets Pierce's disease,” said Natalie Collins, president of the California Association of Winegrape Growers, “it’s a slow death of the vines and it starts to not produce or yield as much fruit.”

The decline can take years, experts say, but eventually, the infected vines will die.

“What we are really trying to do right now,” Collins said, “is ensure that these pests do not make it into California vineyards.”

It won’t be easy.

Between April 21 and May 21, hundreds of potentially infested grape vines were sold at Costco stores in Napa and Sonoma counties. The vines came from a Fresno County nursery.

When plants are shipped from regions known to be infested with glassy-winged sharpshooter, the California Department of Food and Agriculture requires nurseries to flag the orders with a “blue-tag” notice. That lets the receiver know to hold the vines for inspection before selling them.

But, the Fresno nursery didn’t do that.  

“There was no notice with these plants and they shipped and went out to the floors immediately,” said Tracy Cleveland, the agricultural commissioner for Napa County. “Then [they] were sold to customers without being looked at by county ag commissioner offices.”

That’s how impacted vines ended up in people’s backyards.

While residential neighborhoods may be a fair distance from commercial vineyards, Cleveland said, the glassy-winged sharpshooter has a tendency to wander. And it likes to hitchhike.  

“It's a good traveler,” she said, “so it can actually fly long distances.”

And when it gets to its destination, it’s always hungry. Cleveland says feasting on grape vines is how the pest transmits Pierce’s disease.

“Glassy-winged sharpshooter is a voracious feeder,” she said. “It feeds on vines. It has a host list of over 300 different plants.”

Now, ag commissioners across the state are working to contain the spread. That means tracking down and inspecting hundreds of grape vines.  In Napa County, they’ve managed to recover 103 vines out of the 220 sold at Costco.

In Sonoma County, Costco sold more than 600 potentially-impacted vines.

“We're trying to claw back as many of those as we can,” said Andrew Smith, the agricultural commissioner for Sonoma County. “We have somewhere between 100 and 175 still kind of in the wind.”

To help recover the vines, commissioners are asking the public to let them know about any grape vines they’ve recently purchased from Costco. Then, they’ll send someone out to inspect the vines and other plants on the property.

“We're asking them to double-bag their grapevine if they haven't planted it,” Smith said. “Seal that bag and contact our office. If they've planted it, we would appreciate it if they dug it up and double-bagged it and contacted us.”

It’s all part of a coordinated effort between ag commissioners across the state and the California Department of Food and Agriculture. The goal is to make sure the sharpshooter doesn’t get a foothold in wine country.

“We don't have it here in Sonoma County or Napa County. We don't want it here,” Smith said. “This pest is really effective in spreading the disease. You know, it's the last thing we need in our wine grape market in Napa or Sonoma County. “

To report a glassy-winged sharpshooter sighting — the bugs are dark in color with transparent wings and two distinctive white dots on their bodies — contact your local county ag commissioner's office.

.