By TRACIE CONE

Associated Press

FRESNO, Calif. (AP) -- A citrus disease that has killed millions of citrus trees and cost growers billions of dollars across Florida and Brazil has been detected in California, despite the industry's best efforts to keep it at bay.

After a week of testing the U.S. Department of Agriculture confirmed at noon Friday that citrus greening was detected in a lemon-grapefruit hybrid tree in a residential neighborhood of Los Angeles County. Sales and shipments of citrus trees within a 5-mile (8-kilometer) radius of the tree were due to be suspended Saturday.

The disease stands to threaten not only California's nearly $2 billion citrus industry, but treasured backyard trees scattered throughout the state.

"Huanlongbing is called the world's worst disease of citrus," said Dr. Robert Leavitt of the California Department of Food and Agriculture. "It had been present until now in all of the world's major citrus producing areas -- except California."

The bacterial disease, also known as huanglongbing, is carried by the Asian citrus psyllid and attacks a tree's vascular system, producing bitter fruit and eventually killing the tree. Sap-sucking pysllids that feed on an infected tree become carriers of the disease.

It is not a threat to humans.

"It's disappointing," said Joel Nelson of California Citrus Mutual. "Now we'll see if this great program that we believe we have in place is going to work."

State officials were working on a larger quarantine that would extend into northern Orange County. The closest commercial grove is 14 miles (22.5 kilometers) away from the infected tree.

Detection of the disease has been state citrus growers' fear since the bug first crossed into San Diego County from Mexico in 2008, potentially threatening California's fresh citrus market. Despite 25 years of worldwide research, there still are no biological or genetic controls for the disease that keeps fruit from ripening.

The disease is present in Mexico and across the southern U.S., but nowhere is the problem more severe than in Florida, where the disease first appeared in 2005. The University of Florida estimates it has cost 6,600 jobs, $1.3 billion in lost revenue to growers and $3.6 billion in lost economic activity.

The pest and the disease also are present in Texas, Louisiana, Georgia and South Carolina. The states of Arizona, Mississippi and Alabama have detected the pest but not the disease.

California growers and state agricultural officials have been aggressively trapping and testing bugs for the disease since the first sighting four years ago.

"This is the other shoe dropping," said Ted Batkin of the California Citrus Research Board. "We're prepared, and now we'll put our game face on."

The industry group will ramp up trapping efforts and increase testing samples in an effort to keep the disease from crossing into the San Joaquin Valley, where 80 percent of the state's citrus grows. California growers have been contributing $15 million a year to fund efforts to fight both the psyllids and the disease on top of state and federal programs to fight its spread.

"We've been fortunate that we have been able to learn from the experiences of other citrus-growing areas of the world," Leavitt said. "They didn't know they had the psyllid or the disease until it was too late. We have learned from their scientists and have taken a proactive approach."

State officials are making arrangements to remove and dispose of the Los Angeles County tree, which so far is the only one found to be infected. They also will spray all citrus trees for psyllids within a half-mile (800 meters) of the infected tree. Testing on tissue samples from other trees within the half-mile radius is ongoing.

State officials are unsure why Los Angeles County has a higher rate of psyllid infestations than areas closer to the Mexican border. But officials are investigating whether the bugs are hitchhiking through airports and seaports.

Copyright 2012 The Associated Press.