The Mendocino County Agricultural Commissioner announced early this week that laboratory tests on local grapevine samples have not yet confirmed the presence of the glassy-winged sharpshooter (GWSS), an invasive pest that poses a serious threat to California's grape industry. As of June 8, no confirmed detections of GWSS life stages have been found on grapevines purchased at the Ukiah Costco, according to Commissioner Angela Godwin.
Inspections of remaining in-stock plants and samples submitted to the California Department of Food and Agriculture (CDFA) have all tested negative for GWSS, though earlier nymph samples were identified as a different, native sharpshooter species. Some additional lab results are still pending, and heightened surveillance continues.
In a press release last month, Godwin detailed that her staff had completed inspections of grapevine plants shipped from Burchell Nursery in Fresno County to the Ukiah Costco. The county is working with the public to locate, remove, and safely destroy infested plants before the pest can become established.
Recent insect samples are being analyzed by CDFA. The release emphasized that local officials are taking proactive measures in response to confirmed GWSS detections in multiple neighboring counties, including Marin, Sonoma, Solano, Sacramento, and Napa.
Mendocino County has joined other counties in emergency efforts to identify nursery plants purchased at Northern California Costco locations that may be infested.
"This is a very serious threat to our wine industry, which really can’t afford to take a massive hit like this," Godwin told the Mendocino County Board of Supervisors at their June 2 meeting. She assured supervisors that if more life stages are found, she will notify them immediately.
Godwin expressed concern about limited resources and funding, noting that the effort is time-consuming but crucial to protecting the industry. When 5th District Supervisor Ted Williams asked about potential cost recovery, Godwin mentioned discussions about possible legal actions against the nursery in Fresno where the plants originated, but expressed hope that the state would provide emergency funds if the situation escalates.
Specific actions taken in Mendocino County include: Costco voluntarily removed and disposed of all remaining suspect plants from the Ukiah store. Enhanced GWSS detection traps have been deployed at the Ukiah Costco location and surrounding property.
Trap density has significantly increased in the Anderson Valley, a key wine grape production area. The department is working directly with Costco to notify customers who purchased grapevine plants from the Ukiah store between April 24 and May 19, 2026.
Anyone who purchased grapevine plants during this period is asked to keep the plant isolated in its original container, not plant it, and if possible, place it in two secured trash bags until an inspector can respond. Potentially affected plants should not be placed in household trash or compost bins.
Godwin advised residential properties near commercial vineyards to place or increase the density of yellow sticky traps and check them regularly, as GWSS can fly significantly farther than local vectors of Xylella fastidiosa, the bacterium that causes Pierce’s disease. Training for trappers, field workers, and viticulturists to identify GWSS is ongoing, with three ID workshops held at the end of April.
At this time, CDFA is not recommending prophylactic pesticide applications.
An earlier CDFA press release explained that invasive GWSS insects were found on shipments of grapevines sold at select Costco locations in Northern California between April 21 and May 19. Costco is not at fault and has been working cooperatively with CDFA to notify customers, issue refunds, and help connect purchasers with local county agricultural commissioner offices for inspection and disposal guidance.
The CDFA described GWSS as an invasive insect pest that spreads the bacterium causing Pierce’s disease, a fatal grapevine disease that threatens California vineyards. The pest can also damage citrus trees, landscape plants, and other crops.
Early detection and rapid response are critical to preventing further spread. Anyone who purchased a grapevine from Costco in an affected county during that timeframe is urged to contact their local County Agricultural Commissioner’s Office immediately.