The Stanislaus County Agricultural Commissioner is asking residents who recently purchased grape plants from Costco stores not to plant them and to contact the Agricultural Commissioner’s office for inspection guidance following the detection of an invasive agricultural pest on grape nursery stock.

The affected grape plants were sold at California Costco locations, including stores in Turlock, Modesto, and Riverbank between April 21 and May 21.

Agricultural officials are concerned the plants may carry the glassy-winged sharpshooter, an invasive insect capable of spreading Pierce’s disease, a bacterial infection that is often fatal to grapevines.

Glassy-winged sharpshooter detections associated with these shipments have also been reported in multiple Northern California counties.

“Protecting Stanislaus County agriculture and preventing the spread of invasive pests is critically important,” said Stanislaus County Agricultural Commissioner Linda Pinfold. “We are asking anyone who purchased these grape plants to contact our office before planting, moving, or disposing of them.”

Those who purchased grape plants from Costco between April 21 and May 21, 2026, are asked to:

• Immediately contact the Stanislaus County Agricultural Commissioner’s Office at 209-525-4730 or AgCom50@StanCounty.com for inspection instructions.
• Keep the plant isolated in its original pot or container.
• Do not plant, transport, relocate, or attempt to return the plant.
• If possible, place two garbage bags over the plant and secure them tightly.
• Do not place the plant in the trash or compost bin.

Costco is directly notifying customers who purchased the affected grape plants and offering refunds. County agricultural officials are continuing coordination efforts with the California Department of Food and Agriculture and other partners to help identify and contain affected plants.

The glassy-winged sharpshooter feeds on a wide variety of plants and is considered a significant agricultural pest because it can spread Pierce’s disease in grapevines. Areas of Turlock remain under active quarantine and eradication efforts are underway, as part of ongoing statewide prevention efforts.

According to a new economic impact study, the CDFA’s prevention, control and research efforts save California winegrape growers $56 million annually by reducing losses from the fatal grapevine disease. Without the program’s efforts, growers’ losses would more than double from $48 million to $104 million. The study found that if glassy-winged sharpshooters spread unchecked, outbreaks of Pierce’s disease could cost winegrape growers an additional $56 million a year in lost production and vine replacement.