MENDOCINO CO., 6/1/26 — Plants sold at Costco stores around California this spring, the Ukiah warehouse among them, harbored the glassy-winged sharpshooter — an insect that can spread Xylella fastidiosa, the bacterium behind the vine-killing Pierce’s disease. On May 19, inspectors seized and destroyed what was still on the shelves, but the rest had already gone home with shoppers, scattered in backyards across Mendocino County and into Lake County. The state has no sure way to find them.
The Ukiah store may have sold more of them than anywhere else.
“Our store did sell, I think, the largest number of plants before it was caught,” said Lorenzo Pacini, a Mendocino County grape grower who chairs the Mendocino Winegrowers Inc. grower committee, at a May 27 briefing the California Department of Food and Agriculture called for the industry.
“They destroyed all the plants at this store, but we don’t know where the rest of them went — and the Ukiah Valley is our largest grape-growing region in the county,” Pacini said.
The glassy-winged sharpshooter has been in California for decades, mostly in the south and the Central Valley. The North Coast already lives with a native carrier, the blue-green sharpshooter, but it mostly keeps to creekside brush. The glassy-winged kind ranges farther, feeds on a much wider range of plants and travels with nursery stock — which is how a southern pest turned up on a pallet of grapevines in Ukiah. And once Pierce’s disease takes hold in a vine, there is no cure. The vine dies within five years at most.
The vines came from a Fresno County nursery and sold through Costco. The problem surfaced first in Santa Rosa, where Sonoma County inspectors spotted suspect sharpshooters on the plants. Marin County found them next, at the Novato store, from the same shipper. The shipment had arrived with no notice that it needed inspecting. From there, the warning went out to every county that had taken the plants.
Costco has told customers who bought a grapevine since April 21 to call their county agricultural commissioner and have it inspected. The counties are running what they call “trace-forward” — tracking down each sold plant, one buyer at a time.
But the state cannot reach those buyers directly.
“We have inquired with Costco early on,” said Stacie Oswalt of CDFA’s Pierce’s disease control program. “They disclosed that it’s not their policy to give out customer information.” Costco is concerned with the privacy of its members.
Containment now depends on customers reading a Costco message and calling their county ag department on their own. Growers are skeptical that will work.
“Everyone deletes an email from Costco,” Pacini said at the briefing. He pressed the agency to compel the records instead: “I’m pretty sure we could probably get a court order to subpoena Costco’s records. They destroyed all the plants in their store, so I don’t know why we wouldn’t be destroying those plants as well.”
CDFA’s chief counsel, Haig Baghdassarian, said the agency is weighing it. “There may be avenues, as you suggested,” he told Pacini. Because several counties are involved, he said, the state attorney general’s office “may take an interest” and help move faster — something CDFA would be “exploring in the coming hours.”
But obtaining the records might not avert the danger. Michelle Pham, also with the Pierce’s disease control program, said Costco knows which members bought the plants, “but those may not correlate to where those plants actually went.”
Joseph Damiano, the CDFA official who ran the briefing, acknowledged the limits. The plants went “in different places,” he said, and between the emailed notices and the calls that come in, “we may not find everything.” The agency, he said, is “relying on public information to come back.”
In an interview with The Mendocino Voice, Pacini said his frustration at the briefing was aimed at the state, not local officials. The county had moved, he said — Mendocino’s agriculture department sent the first notice, and counties including Napa and Mendocino issued press releases. It was CDFA he could not account for.
“This is the state’s responsibility. This is CDFA’s responsibility,” he said — a problem in several counties at once, which in his view made it the state’s job, not the county’s. “Where have you guys been, and why are you showing up to the party now?”
He said he had to ask the agency directly what it was doing to find the plants. The answer, he said, was that it had talked to Costco, and Costco would not release the buyer list. “And then they ended the sentence.” Pressed on what the plan was from that point, he said what he heard amounted to a promise to send another email in a week.
Lake County faces the same risk. It has no Costco of its own; its growers and residents drive to Ukiah.
“This is extremely concerning to our region as well,” said Jenny Keller, president of the Lake County Winegrape Commission, who also asked the state to get the customer records “if at all possible.” Pacini, who farms in both counties, described the store’s reach: one Costco drawing buyers from Lake County across to northern Sonoma and up toward southern Humboldt.
The vines have been out since late April, more than a month. The sharpshooters found on them turned up in more than one life stage — a sign they could breed, not just travel on the plants. Inspectors also found a single confirmed nymph on a plant sitting next to the grapevines at one store; they pulled the plant and destroyed it, and said the rest of the nearby stock tested clean.
Stuart Spencer, executive director of the Lodi Winegrape Commission, said the window does not stay open long. If the pest settles into the wild, he said, “getting in there and eradicating them is going to be nearly impossible.” In his experience, people who get an email from a store “are not going to be responding quickly.”
So far, the extra traps set at the affected stores and at the homes inspectors have reached have caught no new sharpshooters, though the trace-forward that started May 19 is only a few weeks old. No stores were fumigated; CDFA said treating a building the size of a Costco that way is not practical.
CDFA is asking anyone who bought a grapevine at a Costco since April 21 — in Mendocino, Lake or elsewhere on the North Coast — to call their county agricultural commissioner before the plant goes near a vineyard. Or before it is already in the ground. The agency said it expects to brief the industry again within the week.