California officials warn Costco grapevines may spread a destructive vineyard pest

California agriculture officials are warning that grapevines sold at Costco stores in Wine Country may have carried an invasive insect that can spread Pierce’s disease, a serious vine infection that has caused major vineyard losses in the past.

The California Department of Food and Agriculture said grapevines infested with the glassy-winged sharpshooter were shipped from a Fresno nursery to Costco locations in 24 counties between April 21 and May 21. The affected counties included Napa, Sonoma, Mendocino and Marin, according to state and county officials. Authorities said many of the plants have already been intercepted and destroyed, but thousands of vines may still be with customers who bought them for home use.

Karen Ross, California’s secretary of agriculture, said in a statement that finding those plants is now the main priority. She urged anyone who purchased the vines to contact their local agricultural commissioner at once.

The insect at the center of the alert is a known vector of Pierce’s disease. When the sharpshooter feeds on grapevines, it can transmit the bacterium that blocks the plant’s water system. Infected vines can decline quickly and eventually die. The disease can also affect citrus, almond trees and some ornamental plants.

Officials said the infested vines came from Burchell Nursery in Fresno. The nursery did not immediately respond to requests for comment reported by local media. County officials said it remains unclear why the shipment was not flagged before entering quarantine areas. Under California rules, nurseries in regions where the sharpshooter is present must identify shipments of host plants headed into quarantine zones so local agricultural authorities can inspect them. Marin County Agricultural Commissioner Joe Deviney said that process did not happen in this case.

Deviney said counties involved are taking enforcement action and seizing and destroying infested plants where they are found. He also said Costco was not responsible for the lapse and had cooperated closely with containment efforts.

The plants were sold to individual consumers rather than commercial vineyards, but officials say the risk goes beyond backyard gardening. If infected insects escape into vineyard areas, they could raise control costs, threaten grape supply and create broader pressure on wine production in Northern California. The CDFA has estimated that an unchecked spread of Pierce’s disease could cost the state about $166 million a year.

That threat carries particular weight in Wine Country, where grape growing supports wineries, tasting rooms, tourism businesses and a large share of the regional beverage economy. Any wider outbreak would have the potential to affect vineyard yields and wine availability over time, even if the current incident began with retail sales to home gardeners.

California has dealt with Pierce’s disease before. During a major outbreak in the 1990s, more than 1,000 acres of Northern California grapevines were destroyed between 1994 and 2000, causing about $30 million in damage, according to state figures. The disease leaves vines looking as if they are under severe drought stress because their water-conducting tissues become blocked.

County inspections have already found evidence of the pest in several locations. In Napa County, officials said 63 of the 220 grapevines delivered to a local Costco warehouse were destroyed after signs of infestation were found. One sharpshooter egg mass was detected there. The remaining 157 vines were not accounted for and may already have been sold to customers.

In Sonoma County, officials said staff members found multiple life stages of the insect at Costco’s Santa Rosa warehouse. After contacting Burchell Nursery, county workers determined that the same delivery truck had also dropped off contaminated vines at Costco stores in Rohnert Park and Novato.

State officials are asking anyone who bought grapevines from Costco during the affected period not to move or plant them near other vegetation. The CDFA said customers should keep the vines in their original pots and isolate them from other plants while waiting for inspection. Officials advised double-bagging the vines in trash bags if possible until county inspectors can examine them.

The glassy-winged sharpshooter is larger than many related leafhoppers and feeds heavily on plant fluids. Agricultural authorities consider it especially dangerous because it can travel across many host plants and move disease from one plant to another with little visible warning at first. That makes early detection important in vineyard regions where even limited spread can become costly.

For now, county agricultural commissioners are trying to trace purchases and remove any remaining infested vines before the insects establish themselves more widely in Wine Country.