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Agriculture commissioner reports potential glassy-winged sharpshooter finds linked to Costco plant sales
Summary
Mariposa County Agriculture Commissioner Monica Nielsen reported inspections of 14 locations with 29 suspect grapevines linked to Costco; two locations had plants seized and destroyed and samples were sent to CDFA for confirmation. One property refused inspection and could be treated as ground zero if infestation is confirmed.
Mariposa County Agriculture Commissioner Monica Nielsen told the Board of Supervisors on June 16 that the California Department of Food and Agriculture (CDFA) is investigating possible glassy-winged sharpshooter (GWSS) infestations tied to grapevine purchases from Costco.
Nielsen said county investigators identified 29 plants at 14 locations. To date, two locations had plants seized and destroyed and personnel recovered a nymph molt that was sent to the CDFA laboratory for confirmation. She said traps have been deployed at all locations, including those currently free and clear, and that one property owner has refused inspection.
"If we were to get an infestation, they are going to be considered ground zero, and we'll start trace back from that location," Nielsen said, explaining that a ground-zero determination would trigger further enforcement steps and possible involvement from the district attorney’s office.
Supervisor questions focused on spread potential and proximity to vineyards. Enrique Smelcom/Smallcomb (transcript name variation) asked about the distance to the nearest vineyard; Nielsen said one suspect location is within approximately two miles of a grape vineyard and confirmed deploying traps countywide at identified addresses.
Nielsen emphasized the pest's agricultural risk: GWSS vectors Pierce's disease, which can kill grapevines within two years and threatens local viticulture and associated agricultural commodities; she said the pest poses no direct human or animal health threat.
The board thanked Nielsen and urged continued outreach to purchasers and monitoring; Nielsen said CDFA requested revised emergency work plans and that county staff would update the contract and reporting as requested.
