Agricultural officials rejected a nursery load at a Napa, Calif. retailer after officials discovered viable glassy-winged sharpshooter (GWSS) egg masses on two crape myrtle trees shipped from San Diego County.

The nursery stock was returned to the original nursery and the egg masses were destroyed. Entomologists with the California Department of Food and Agriculture verified the viability of the egg masses.

The announcement from Napa County Ag Commissioner Greg Clark highlights the county’s proactive effort to keep the GWSS out of Napa County and protect the county's wine grape industry, which last year was valued at more than $656.2 million in grape sales alone.

“We have been successful in keeping GWSS out of Napa County for 14 years,” Clark said. “This recent discovery of viable GWSS egg masses points to the continued importance of our GWSS exclusion and detection programs.”

Assistant Ag Commissioner Humberto Izquierdo said Napa County’s vigilance in the matter led to a local policy that inspects all shipments delivered to retail nurseries, regardless of whether the product comes from a quarantine zone.

In this case, the shipments did not originate from a quarantine zone, but some of the materials in those shipments could have originated from within a GWSS quarantine, Izquierdo said.

Izquierdo says local grape growers have assessed themselves for GWSS protection based on vineyard production. Assessment dollars help fund state efforts to keep the GWSS out of Napa County.

“We have a lot of concern over the glassy-winged sharpshooter here,” Izquierdo said. “We’re very aggressive in our approach.”

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The glassy-winged sharpshooter spreads Pierce’s disease, a bacterial disease which kills grapevines. There is no known cure for Pierce’s disease.

Adults sharpshooters are strong flyers which can lay eggs in the vineyard. GWSS prefers to feed on a variety of plants; increasing the likelihood that it can pick up and spread the disease.