‘We do not want this stuff getting out': More Costco plants found with invasive pest

A second wave of Costco plant shipments has been found carrying evidence of an invasive insect that can spread a fatal grapevine disease, widening concern among California agriculture officials already trying to track down thousands of potentially infested grapevines sold this spring.

Desert willow plants shipped last week to Costco stores in Sacramento and Marin counties had viable egg masses of the glassy-winged sharpshooter on their leaves, according to state agricultural officials.

The pest does not harm people or animals, but it can spread Pierce's disease, a bacterial infection that can kill grapevines and threaten wine and table grape production.

The new findings come less than two months after glassy-winged sharpshooters were found on grapevines shipped from a Fresno County nursery and sold at Costco stores in Northern California between April 21 and May 21.

The California Department of Food and Agriculture has urged anyone who bought grapevines from Costco in affected counties during that period to isolate the plants and contact their local agricultural commissioner immediately.

The latest desert willow shipment was expected at more than 85 Costco locations statewide, according to an email between county agricultural offices obtained by the Sacramento Bee.

The outlet reported that the plants were shipped from a nursery in Tyler, Texas and that some may have been sold before inspectors could destroy them.

In Sacramento County, agricultural inspectors destroyed 209 of 215 infested desert willows at Costco stores, Agricultural Commissioner Chris Flores told the Bee. Six plants remained unaccounted for.

"The counties are being very diligent in trapping and trying to alert our nurseries to give us calls," Flores said. "We do not want this stuff getting out."

In Marin County, Agricultural Commissioner Joe Deviney told the newspaper that Costco asked his office Friday morning to inspect the desert willows, even though the shipment did not have the required inspection paperwork when it arrived at the retailer.

Inspectors found six egg masses in various stages of development, including two that showed the pests had already emerged, Deviney told the Bee. His office destroyed all 24 desert willows in the shipment before any were sold.

The CDFA's public Costco alert, last updated June 26, still focused on the earlier grapevine shipments.

The agency said glassy-winged sharpshooters had been found on grapevines sold at select Costco stores in Northern California and that early detection and rapid response are critical to preventing the pest from spreading.

CDFA says the glassy-winged sharpshooter feeds on the xylem fluid of many plants, builds large populations on a wide range of hosts and can fly farther than native sharpshooters.

Caleb Mosley, executive director of Napa Valley Grapegrowers, said in an interview with the Chronicle earlier this month that Napa County had traced roughly half of about 200 to 220 Costco grapevines and removed and destroyed about 100.

Egg masses were found on four plants, he said.

"The major push right now, we're still in this period of trying to get the word out to people who purchased plants from Costco during that time frame to call the agricultural commissioner," Mosley said. "The more of those we can do, the safer we're going to feel."

Mosley said the fact that the Costco grapevines were sold for home use does not make them harmless. It makes them harder to track. Once the vines left the store, they could have been planted almost anywhere - in residential neighborhoods, near creek corridors or close to commercial vineyards.

"It's a scatterplot," Mosley said. "Some could have gone to densely residential areas, some might be planted next to a commercial vineyard or a riparian corridor."

CDFA said Costco is offering full refunds to customers who bought the vines and that customers do not need to return the plants to get a refund.

Agriculture officials are telling customers not to move, return, throw away or compost suspect plants. CDFA says grapevines should be kept in their original containers, isolated from other plants and, if possible, double-bagged while awaiting inspection.

The stakes are high for California agriculture. CDFA said a 2025 economic study estimated Pierce's disease could cost California about $166 million a year if left unchecked.

In a letter this month, U.S. Sens. Alex Padilla and Adam Schiff and 12 California House members asked U.S. Agriculture Secretary Brooke Rollins to release $32.2 million in emergency funds for tracing, surveying, trapping and longer-term eradication work.

The lawmakers said infested nursery stock identified May 19 had been distributed to Costco stores in 24 counties and that vines sold to customers were believed to have been transported to homes in at least 38 counties.

For growers, the threat arrives during an already difficult period marked by weak wine demand, rising costs and other vineyard diseases.

"All the other stuff remains," Mosley said. "Leafroll. Red blotch. Regulation. Weak market. If you think about it all at the same time, your head will explode."

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