Border agents have stepped up searches and hundreds of traps have been placed on the California-Mexico line in an aggressive campaign to stop a tiny bug from bringing in a disease farmers say could wipe out the $1.3 billion citrus industry here.

Already, Asian citrus psyllid has hurt citrus production in parts of China and infested millions of dead and dying trees in Florida and Brazil. Growers say the bug has the potential to be more damaging than the Mediterranean fruit fly because entire groves _ not just fruit _ are at risk.

"This is not one more thing, this might be the last thing," said Al Stehly, who manages 200 acres of oranges near Valley Center in San Diego County.

The tiny psyllids are the only transmitters of the disease, officially known by its Chinese name, huanglongbing, or "yellow dragon disease" for its visual effect on leaves. In the U.S., growers call it "citrus greening" disease because fruit fails to ripen.

Psyllids feed on the liquid inside citrus leaves, and once a psyllid eats from an infected tree, it carries the bacteria for life. Diseased trees wither and die within a few years.

More than 22 years of research by the U.S. Department of Agriculture has not yet revealed genetic or biological controls for the disease.

"There is no place in the world this disease is under adequate control," said plant pathologist Tim Gottwald of the USDA's agricultural research service in Florida and one of the world's leading authorities on citrus greening. "We don't have an adequate strategy at this moment."

Gottwald likens the potential impact to Dutch elm disease, which has wiped out nearly the entire elm population in England and Europe.

Recent news that the bug was found within four blocks of the San Diego County line sent orange juice futures up and spread panic through the industry. Industry officials worry international trade could be affected, as California supplies 85 percent of the U.S. fresh orange market, and 30 percent of the state's production is shipped overseas.

"The sky could fall unless everybody is constantly on top of everything on this," said Christopher Mundt, a plant epidemiologist at Oregon State University who studies grains, but was asked recently to bring fresh eyes to the citrus problem. "There's not going to be much room for error on this one."

DNA tests on 138 psyllids trapped so far in Tijuana have given no indication those bugs carry the bacteria.

Still, officials are being vigilant.

Border patrol agents have stepped up monitoring for orange tree cuttings and even certain types of curry leaves at airports and crossings. Some nursery ornamentals such as mock oranges and certain orange jasmines can be silent carriers of the disease. Officials also worry that citrus greening already could be present in California but until now has lacked a carrier.

California agricultural officials have placed 1,065 traps in a 120-square-mile grid at the border in San Diego and Imperial counties.

"Unfortunately, pests don't observe international borders," said Steve Lyle of the California Department of Agriculture. "Should the pest cross the border, and there's little reason to believe that it won't, we'll be able to detect it as fast as we can."

After that, agriculture officials say they aren't sure what they'll do and that "response options are under evaluation."

The California Citrus Research Board also is launching its own fight Friday, enlisting growers and master gardeners from San Diego to Ventura to help bait and trap the bug by pruning sentinel trees to encourage the new growth the psyllids favor. It will form a line of defense against the San Joaquin Valley, where 80 percent of the state's oranges grow.

The group, funded by state growers, will also set up labs in Riverside and Tulare counties to expedite testing for the disease on suspect trees. The cost will be about $1.5 million a year.

"We're throwing everything at it but the kitchen sink," said Ted Batkin, the board's president.

The bugs arrived in the U.S. in Florida in 1998, and the disease was in full-swing by 2005. Costly spraying of a variety of insecticides toxic to bees and beneficial insects and wildlife have been used to combat the disease's spread in an effort to protect the state's $9 billion a year industry.

Florida growers have contributed more than $20 million for research this year.

In June, an infected backyard tree outside of New Orleans prompted a statewide quarantine in Louisiana. That was the disease's first U.S. appearance outside of Florida.

While defending against the bug has proved difficult, one long-term solution, Gottwald said, could be to build genetic resistance into the trees.

"That has to be augmented with short-term solutions to keep the industry alive," he said.

The cost to farmers has been hard to assess since prices rise when supply falls. But increased spraying alone increases production costs by one-third, said Tom Spreen, chairman of the University of Florida's food and resource economics department and one of the country's three citrus economists.

When the disease hits, growers must decide whether to cull and replace trees, or abandon operations.

"We can slow it down," Stehly said, "but we can't stop it. I'll be out of business in a few years."

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On the net:

http://www.CaliforniaCitrusThreat.org