Insect’s Spread Poses Threat to State’s Vineyards

When Joe Kretsch looked into the jar of ugly-looking bugs, he knew the war against the latest voracious pest to threaten California agriculture had finally reached his doorstep.

Inside the jar were half a dozen glassy-winged sharpshooter nymphs from a friend’s backyard vine--confirmation that infestation has spread to the heart of the Central Valley, state agriculture officials said this week.

The discovery significantly raises the stakes in the escalating battle against what scientists call the most serious threat ever to California grape production.

“It’s kind of like the alarm bell,” said Kretsch, a pest management specialist for raisin producer Sun-Maid Growers of California.

The glassy-winged sharpshooter already has infested Southern California, destroying $40 million worth of grapevines in the Temecula area alone. Researchers at the University of California estimate it will cost $52 million to replace dead and dying oleander, another host plant, along 2,100 miles of state highway.

Kretsch’s find was on the southern outskirts of Fresno. On Wednesday, local officials reported another discovery, this time an adult sharpshooter found at an apartment downtown. With $605 million in grapes at stake in Fresno County, worried growers have been flooding local Agricultural Commissioner Jerry Prieto’s office with calls seeking information.

Saying the sharpshooter is “just as serious a threat to agriculture” as the Mediterranean fruit fly, Prieto ordered crews into the field with traps to figure out how far the infestation has spread.

But while the insect’s entry into the Central San Joaquin Valley is alarming, just as worrisome is the sharpshooter’s steady northward march toward California’s premier wine country. If the sharpshooter reaches the Napa Valley, said Napa County Agricultural Commissioner Dave Whitmer, it would be like “striking a match in a forest.”

The glassy-winged sharpshooter is a monster of a bug. At half an inch long, it is bigger and stronger than many leafhopper cousins, with a needle-sharp proboscis that it uses to stab plants and suck out their nutrients. But its appetite is not what makes it dangerous.

The insect carries a bacterium, Xylella fastidiosa, which causes Pierce’s disease. The disease, which is incurable, clogs a plant’s water-carrying tissues so that it slowly dies of thirst. The sharpshooter picks up the bacterium while feeding on infected plants and carries the disease to healthy plants.

Pierce’s disease is a familiar enemy to California growers. Outbreaks date back more than 100 years. In the 1880s, the disease destroyed 40,000 acres of wine grapes in Anaheim. Found in riparian areas, and also carried by a puny relative of the glassy-winged sharpshooter called the blue-green sharpshooter, the disease continues to cause serious losses in the Napa Valley. Last year, north coast growers lost $46 million to the disease.

The blue-green sharpshooter, a weak flier, can only nibble at the edges of a field. The glassy-winged-sharpshooter is considered more dangerous because it can spread damage over a wide area. The bug’s mouth parts are also powerful enough to stab into the stem of the plant, spreading the disease into the plant’s heart.

Also, it breeds prodigiously. “The glassy-winged sharpshooter and the diseases it vectors are possibly two of the greatest threats ever to California agriculture,” Richard Redak, associate professor of entomology at UC Riverside, told an Assembly committee last fall.

For a long time, California farmers didn’t worry much about the glassy-winged sharpshooter. It is native to the Southeastern United States and Northern Mexico. Then, in the early 1990s, the bug began showing up in Southern California, particularly in nursery stock and citrus groves.

Still, there was no real concern until an outbreak of Pierce’s struck Temecula in 1997. Researchers traced the outbreak to the glassy-winged sharpshooter, but by the time scientists understood the new threat, it was already well established in Southern California.

So far, 20% of the Temecula region’s 2,300 acres of vines have been lost, according to Riverside County Assistant Agricultural Commissioner Cal Kaminskas.

The future could be even bleaker. Kaminskas said up to 75% of the vines in the Temecula area may be infected with Pierce’s disease.

As that outbreak worsened, the insects spread in the ornamental oleander along highways in Southern California, particularly in Orange County.

“Since becoming established in Southern California, the glassy-winged sharpshooter-Xylella association has eliminated oleander as the plant of choice for California roadways,” Redak said in a statement.

Ominous Discovery

So far, the spread of oleander leaf scorch has not been detected north of the Tehachapi, said Jim Drago, a Caltrans spokesman.

Individual glassy-winged sharpshooters have been found outside Southern California, but most were on nursery plants from the Los Angeles area. That encouraged farm leaders hoping to contain the insect.

Then, on May 17, three bugs were found in the Tulare County community of Porterville. The more investigators looked, the more they found.

The infestation there has grown to nine square miles, said Steve Lyle, a spokesman for the California Department of Food and Agriculture. Because Tulare County is also an important grape-growing region, this was a serious development. Two days after the Porterville discovery, Gov. Gray Davis signed legislation by state Sen. Wesley Chesbro (D-Arcata) providing nearly $7 million for eradication of and research on the glassy-winged sharpshooter and Pierce’s disease.

Davis also sent a letter to U.S. Secretary of Agriculture Dan Glickman requesting help. A week later, Congress approved another $7 million for the battle against the sharpshooter.

In Fresno County, where more than 230,000 acres of grapes are harvested each year, residents understand how closely their fortunes are tied to those of agriculture. Though the economy is much more diversified than in the past, residents pride themselves on their farm roots. As word spread of the infestation’s approach, county entomologist Norman Smith found himself inspecting 35 to 40 insects sent in each day for analysis.

“Napa and Sonoma have put pressure on us to stop it here,” Smith said. “You don’t want to have a continuum all the way to Napa.”

Crews like one headed by Wayne Peregrin recently combed Fresno’s suburban undergrowth. “These things are very intelligent for a bug,” said Peregrin, a county agricultural worker. They hide on the other side of the branch when the tree is approached.

The best way to find them, he said, is “thwapping.” That involves hitting a branch with a stick and sweeping a net under it. Employing the technique on a sycamore in a neighborhood of $500,000 homes, Peregrin came up with an Argentine ant and a lacewing, but no sharpshooters.

A few days later, Sun-Maid’s Kretsch got a call from a friend who wanted him to look at some insects he found.

“No one likes looking at something that could devastate your industry,” Kretsch said.

By Monday, Commissioner Prieto knew he had an infestation. “There’s no telling how large it is,” he said, as workers fanned out in the residential neighborhoods near the site where the insects were discovered. On Wednesday, the lone adult bug was found downtown.

Natural Enemies

The sharpshooter battle plan, officials say, has been to try to contain the insect and minimize its damage while scientists search for answers.

They have visited the bug’s native habitat looking for natural enemies. Several parasitic wasps are

being tested at UC Riverside’s quarantine facility to make sure that they are effective and that they only eat sharpshooter eggs. If they prove to be successful, the tiny wasps, which do not sting humans, could be raised by the millions and released into infested areas.

The trouble is, it will be a few years before the prey insects are ready for release. Nobody knows where the infestation will be then.

In Temecula, growers are treating their fields with a pesticide called Admire, but it’s too early to know the results.

When it comes to residential areas such as Porterville and Fresno, the problem is more difficult. Public health concerns make spraying an unpalatable alternative in populated areas. A panel of scientists is due to make its recommendations this week on whether to spray in Porterville.

Lyle acknowledged that the glassy-winged sharpshooter was allowed to spread unchecked in Southern California. But he said that’s because no one knew that it would be such an effective carrier of Pierce’s disease.

“We didn’t know what we had in Southern California,” said Lyle. “We can understand the criticism, but it’s easy to Monday morning quarterback. We think we’re taking steps to control it.”

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Times staff writer James Ricci contributed to this story.