Second Pest Threatens State Vineyards : Viticulture: The sharpshooter not only feeds on young vines, but also serves as a carrier for a harmful bacterium.

California’s wine industry, still hurting from the root-eating pest phylloxera, now faces a threat from a bug that is spreading a deadly microbe through vineyards.

The new pest is a quarter-inch-long insect called the sharpshooter, which is attacking vineyards in the wine country north of San Francisco.

The insect feeds on many different plants, including young grapevines, sucking the sap. It does not kill the plants directly but carries xylella fastidiosa, a bacterium that causes many maladies, including the fatal Pierce’s disease.

Pierce’s disease, once called Anaheim disease, destroyed virtually all the vineyards in Orange County earlier in the century. In recent years it has affected vines in San Diego County, but this is apparently the first time it has hit Northern California.

“It is the viticultural problem we have the highest anxiety about,” said Mike Walsh, owner of Walsh Vineyard Management in Napa.

About 200 acres of the 1,800 acres of vineyard he manages are seriously affected by Pierce’s disease, and the problem may be more widespread than previously believed.

“The especially disturbing thing is that the disease is particularly hard on young vines, and we have new vineyards in many of the most problematic areas,” he said.

The sharpshooter is the latest problem to hit California’s wine industry. For the past 10 years, growers have had to cope with phylloxera, a tiny, aphid-like louse that has killed thousands of acres of vines. Increased competition, scarcity of credit and a drop in wine consumption have also harmed the industry.

The sharpshooter is worrisome because it is impossible to kill all the insects in an area. It tends to affect vines next to brush and forests, so some growers are trying to control the pest by cutting back wild growth along the edges of their vineyards.

Researchers hope to determine whether some rootstocks might resist Pierce’s disease as they do phylloxera. There is some evidence that is the case, said Andrew Walker, a rootstock breeder and assistant professor of plant genetics at University of California, Davis. Walker is helping set up a series of rootstock experiments.

“It’s very hard to get funding during periods of low Pierce’s disease incidence for trials like this, but we’re seeing lots of interest these days,” he said.