Hopes raised in fight against sharpshooter

Genetic discovery may help grapevines resist costly disease

Eric Brazil / SF Chronicle 21may01

The glassy-winged sharpshooter The glassy-winged sharpshooter spreads Pierce's disease, which is lethal to grapevines.

  • Color and size: Brown, a half-inch long.

  • Its name: From its large proboscis, which it uses to drill into a plant's tissue to suck out fluid.

  • Diet: Feeds on a variety of common plants and infests them with Xylella fastidiosa bacterium, which attacks the plant's xylem, or water-conducting tissues, and eventually chokes off water and nutrient supplies.

  • Favorite haunts: Ash, citrus, sycamore, macadamia, crape myrtle and grapevines.

  • Nuisance: When the insects infest tree canopies, their watery excretions fall on people, cars, picnic tables and sidewalks.

  • Control: Insecticide can kill the sharpshooter but probably not fast enough to prevent it from transmitting Pierce's disease.

Sources: UC Davis, California Dept. of Food & Agriculture, photo courtesy of UC Berkeley. Pesticide figures from the state Department of Pesticide Regulation; figures are for 1998, the most recent available. Chronicle Graphic

Mad cow disease, hoof and mouth disease and the energy crisis have pushed the glassy-winged sharpshooter off the front pages lately, but California grape growers remain on red alert to repel a pest they view as the Darth Vader of the insect world.

They're buying time with plant inspections, chemical spraying, field trials and a public education campaign to keep the sharpshooter at bay. The insect carries bacteria that cause Pierce's disease, which is invariably fatal to grapevines.

Growers are hoping that science will come to the rescue soon with ways to engineer plants that are genetically resistant to infection. And such help may be on the way: The University of Florida announced last week that patents have been issued for a group of resistance genes in grapevines, an early step toward developing what many growers consider the ultimate solution.

In the long run, "controlling the sharpshooter is not going to be an effective means of defeating this disease," said Dale Brown of St. Helena, president of the Napa Valley Grape Growers Association. "Genetic resistance is where we want to go."

Until that resistance becomes available to growers, their main weapon is a $40 million state-federal counteroffensive begun last summer against the sharpshooter.

The campaign is paying for a beefed-up plant inspection service which examines all plant materials shipped from areas of known infestation by the glassy-winged sharpshooters. It is also financing a variety of field trials on 13,000 acres in infested Kern County, where chemical and organic materials are being tried to control the pest.

The panic that swept through the grape growing industry last year has subsided, said Sonoma County Agricultural Commissioner John Westoby, whose office has added nine plant inspectors to keep an eye out for the glassy- winged sharpshooter in incoming plant shipments.

"I think there seems to be less pressure this year. There are still as many plant shipments, but nurseries in California are doing an excellent job of making sure their plant materials are as clean as possible," he said. "There's tighter control on the commercial movement of plant material, so we're not quite as anxious."

Two statewide vineyard surveys found no new infestations and reduced numbers of sharpshooters in the 13 counties where infestations were reported last year.

The glassy-winged sharpshooter's potential for spreading to Napa County is a major threat, Brown said. He speaks from experience.

"My own (chardonnay) vineyard was reduced by one-third" by Pierce's disease,

he said. It was transmitted by the endemic blue-green sharpshooter, "which is like a big mosquito. It doesn't travel very far. The glassy-winged is the B-52 of sharpshooters."

Sonoma and Napa counties have established a Web site -- www.bugspot.org -- urging residents to "be a sharpshooter spotter." And in Napa County, the board of supervisors has proclaimed May "Sharpshooter Awareness Month." Sharpshooter posters abound, and trees are festooned with sharpshooter detection traps.

California's multibillion-dollar wine industry has every reason to fear the spread of Pierce's disease, said Dennis Gray, a professor of developmental biology at the University of Florida, who leads the latest research effort.

Pierce's disease clogs a plant's water-transporting vessels and causes it to wither and die. It destroyed Florida's grape-growing industry in the early 1900s.

"If California's future with Pierce's disease is anything like Florida's past, the grape industry will be severely threatened," said Gray, a Modesto native who teaches and does research at Florida University's Mid-Florida Research Center in Apopka.

The Florida university researchers have been working on genetic resistance to Pierce's disease in cooperation with the U.S. Department of Agriculture for more than a decade.

The genes they have discovered are a synthetic version of those found in a variety of organisms, such as silkworm larvae, which use genes to kill bacteria and fungi. Gray said that in laboratory conditions, the protein produced by the gene kills the Pierce's disease bacterium.

But no one expects a quick fix.

"Assuming everything goes according to plan, it will be a bare, bare minimum of five years, more likely eight or so years," before resistant plant material -- or the technique for developing it -- will be available, Gray said.

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