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Signs of Vineyard Pest Found Again in Napa

County is on alert against the glassy-winged sharpshooter, which spreads a vine-killing disease

Daniel Sogg

Posted: Thursday, May 25, 2006

Spring in Napa means more than the beginning of vine growth. It's also the peak alert season for the glassy-winged sharpshooter, the leaf-hopping insect that transmits the fatal, as-yet-incurable vine malady known as Pierce's disease. Since April 4, Napa County agricultural inspectors have discovered a total of five viable sharpshooter egg masses on four plant shipments originating from nurseries in Southern California, where the insect is already entrenched.

The inspection program, which has been in place since 2000, is Napa County's prime defense against the glassy-winged sharpshooter, which has yet to establish a foothold in Northern California's most prestigious winegrowing appellations. The county also targets all residents with awareness campaigns, to enlist them in the fight to identify and intercept any new arrivals of the insect.

Pierce's disease has been present in California since the 19th century and already occurs in Napa, where it is spread there by a less vigorous insect, the blue-green sharpshooter. The glassy-winged sharpshooter is of much greater concern because it is bigger, travels farther and feeds on a wide range of plants, allowing it to spread rapidly. After it infested Southern California's Temecula appellation in the 1990s, hundreds of acres of vineyards were wiped out by Pierce's disease.

Every year, agricultural inspectors face the same challenge. Beginning in April, growers in Southern California accelerate plant shipments to nurseries, retail stores and landscapers located in Napa and other neighboring areas in the northern part of the state. According to Napa County agricultural commissioner Dave Whitmer, his inspectors have already received more than 2,200 plant shipments of the more than 3,000 anticipated this year.

Five full-time Napa staffers inspect the shipments, which can contain hundreds of different plants. By law, both the shipper in Southern California and the receiving nursery must alert the county of incoming shipments. In the case of the most recent infested shipment, which arrived in Napa on May 17, the receiver failed to contact agricultural inspectors. That could result in the county taking disciplinary action, which can range from a warning letter to revocation of the nursery license.

Nonetheless, Whitmer says that the nursery industry has been cooperative. "They've really been team players. From the wine industry perspective the nurseries have been very engaged. The largest number of nurseries that are shipping are trying to be in compliance," he said.

Whitmer emphasizes that even though the inspection program has apparently been successful so far--no infestations of live insects have been discovered in Napa--concerns remain and the county must be vigilant. "For us, it's one of those life or death fights," he said. "The threat is very real, and it's important that folks stay engaged and that we maintain the same level of awareness."

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