Pierce’s Disease Spreads in Kern

After devastating the Temecula wine region, the dreaded vineyard scourge of Pierce’s disease appears to be spreading across the southern half of the state’s second-largest grape growing area, Kern County.

In one corner east of Bakersfield alone, the vine-shriveling disease has been confirmed in a dozen vineyards, and farmers and government officials are pulling out more than 600 infected vines, according to UC farm advisor Jennifer Hashim.

“It’s a lot more widespread in the area than we originally thought,” said Hashim, who has been working on a state and federally funded program to control the disease.

Since it usually takes a year or two for symptoms of Pierce’s disease to show up after a plant has been infected, it’s likely that more confirmed cases will start showing up, said Nick Toscano, UC Riverside entomologist.

Although Pierce’s disease has existed in Kern County and other parts of California in low levels for decades, it took a particular nasty bug, the glassy-winged sharpshooter, to raise the problem to epidemic proportions.

Introduced to California about a decade ago, the flying insect covers large distances, carrying a deadly bacteria in its mouth, Xylella fastidiosa , which is transferred to grapevines during feeding. Once infected, the plant’s tissues become clogged and water and nutrients can’t get to its leaves and fruit.

The disease has wiped out 1,000 acres of wine grapes in Temecula over the last decade, costing growers an estimated $40million in damages.

In Kern County, the stakes are even higher: Grapes are a $438-million business, cultivated on 86,000 acres. That acreage is split almost equally between table grapes, grapes for wine and raisin grapes.

Although there had been a marked increase in the numbers of glassy-winged sharpshooters caught in the county in the last two years, both county agriculture officials and industry officials had hoped they could use pesticides and other treatments to keep the insect from settling into the area’s vineyards.

“Perhaps we all had been lulled into thinking that it would not move across the Tehachapis,” said Karen Ross, president of the California Assn. of Winegrape Growers. “But now that it’s moved into the Central Valley, it’s increased the potential for this thing to spread farther.”

Growers in the southern half of the county have started spraying more pesticides on their grapes to kill the sharpshooter and are urging their neighbors to do the same. In the 13,000-acre test area that Hashim is monitoring, state food and agriculture officials are paying for applications of a clay-based repellent and the release of parasitic wasps, which eat the sharpshooter’s eggs.

All of these strategies are only attempts to contain the pest. So far, there is no cure for the disease itself. Vines that show symptoms typically are too far gone to survive, Hashim said.

State and federal agriculture officials have spent about $50 million to study and try to contain the pest before it spreads to grapevines farther north.

Kern County grape grower Jack Pandol worries that with the diverse array of fruit and plants in Kern County that the sharpshooter likes to feed on, it may be hard to stop. And with farm prices low for raisins and area wine grapes, he fears that his neighboring growers might not be able to spend the money on pesticides and other treatments to fight the pest.

“Vigilance is required,” Pandol said. “If we sit here on our rear ends and do nothing, we’ll lose the battle.”