"I would have guessed it was a little bit low," said Alexander "Sandy" Purcell, insect biologist at the University of California, Berkeley. He didn't speculate as to how much worse the problem may be, however.

Purcell, one of leading scientists involved in the expanding fight against Pierce's Disease, was among more than 150 researchers, growers and agriculture officials who attended a three-day Pierce's Disease symposium this week in San Diego.

The event included updates from nearly 70 scientists who have received more than $12 million to study Pierce's Disease and the glassy winged sharpshooter, the insect that spreads a scourge that wiped out the grape industry in Anaheim more than a hundred years ago.

"We are heading in the right direction," Williams Lyons, secretary of the California Department of Food and Agriculture told the audience. "We still have a lot of work to do."

He said more attention needs to be focused on long-term ways to deal with the bacteria that causes the disease than the hard-flying insect that spreads it.

"We must strive to cure this disease, not just control the vector," he said.

Results from a partial survey of Temecula vineyards recently showed that Pierce's Disease has infected or killed about half the region's grape vines.

But based on the glassy-winged sharpshooter's ability to spread the disease and its long-standing presence in Temecula, Purcell said he suspects that more than 50 percent of Temecula's 2,500 acres of vineyards may be at risk.

The price tag associated with replacing vines killed by the bacterium that causes Pierce's Disease was estimated as high as $22 million. That does not include lost grape production.

Previously it was thought that a third of Temecula's vineyards were infected with Pierce's Disease, which resulted in a loss of $9 million.

In 1999, scientists estimated that infection rates in Temecula vineyards ranged from a low of 10 percent to as high as 90 percent.

The spread of the disease was linked to type of grape being grown and how close the vineyard was to citrus, the sharpshooter's favorite nesting place.

Some grape varieties, such as Temecula's popular chardonnay, are more susceptible to Pierce's Disease than other grapes.

Scientists suggest that high infection rates may make it uneconomical to grow grapes in some Temecula vineyards.

"If it's more than 50 percent, does it really matter?" said Matthew Blua, entomologist at the University of California, Riverside.

Instances where Pierce's Disease is present throughout the vineyard would obviously be more serious than if the disease were discovered only on one side of the vineyard, he said.

Economics also depend on whether the grower is using the grapes to make wine or is selling them to a winery, he said.

Reach Don McAuliffe at (909) 587-3127 or dmcauliffe@pe.com