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California Growers Battle Carrier of Pierce's Disease

Lynn Alley
Posted: February 14, 2000

With spring just around the corner, grapegrowers in Southern California are gearing up for a full frontal assault on the glassy-winged sharpshooter, the insect responsible for the rapid spread of deadly Pierce's disease in the region's vineyards.

Fearing that the disease could soon threaten vineyards throughout California, the wine industry, local governments, the state and the federal government have kicked in a total of $1.7 million so far to fight the pest, according to Patrick Gleason, director of the American Vineyard Foundation in Napa. Requests for more funding from the federal government are pending.

No known cure exists for Pierce's disease, which is caused by a bacteria that is typically carried by insects. Infected vines usually die within one to five years, with productivity diminishing along the way.

For more than a century, California vineyards have been faced with sporadic outbreaks of P.D. However, this time around, the disease is being carried by a new, far-flying pest -- the glassy-winged sharpshooter, which experts believe was introduced into southern California in 1990 via ornamental plants from the southeastern United States. Last year alone, Temecula growers lost more than 350 acres to the disease.

Beginning in late February or early March, helicopters will spray a sharpshooter-killing organophosphate over 240 acres of Temecula citrus groves, where the adult bugs winter and lay their eggs. Then, in March, growers will apply a systemic insecticide to the roots of the trees to kill off the first generation of young sharpshooters as they hatch, before the insects move back into the budding vineyards.

Other growers are experimenting with more unconventional methods of control, such as biodynamic vineyard practices and a tetracycline screw that is inserted into vines. "We're making a concerted effort to leave no stone unturned in the battle to save the vineyards," said Craig Weaver, vineyard manager at Callaway Vineyard & Winery.

Meanwhile, many growers in California's North Coast are clamoring for their counties to institute a quarantine of all ornamental plants from the southern portion of the state. No action has been taken yet.

However, the Nursery Growers Association has agreed to jump into the fight to control the spread of the insect via ornamental and other plants. Voluntary education and inspection programs are currently being instituted in nurseries in Ventura and Los Angeles counties.

Regardless of these efforts, the glassy-winged sharpshooter has already gained a strong-enough foothold in some areas to allow it to spread to larger wine-producing regions of California. The pest has now firmly established itself in the few small vineyards in Ventura County, just south of Santa Barbara County, and in grape plantings in Kern County, around Bakersfield, which is to the northeast of the Santa Barbara region.

"All but one of our vineyards is now infested with the glassy-winged sharpshooter," said Phil Phillips, farm advisor of Ventura County, where the bug also lives in laurel sumac, not just citrus trees. "We suspect that the laurel sumac found in the coastal ranges will offer the insect a means to leapfrog from Ventura County into the vineyards of Santa Barbara and San Luis Obispo counties," he added. "Just how long this will take is anyone's guess."

And now that the problem is found in Kern County, Phillips pointed out, "The sharpshooter can easily go south, or north up Highway 99 all the way to the Sacramento Valley, with virtually nothing to slow its progress."

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For past news on the problem:

  • Oct. 13, 1999
    New Pierce's Disease Carrier Spreads to Lodi

  • Sept. 16, 1999
    Pierce's Disease Devastates Vineyards in California's Temecula Region

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