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Deadly citrus disease reaches Mexico, threatens California

Citrus greening disease, described by one expert as 'a citrus grower's worst nightmare,' is spread by an infestation of the Asian citrus psyllid.

August 18, 2009|Jerry Hirsch

Leaders of California's $1.6-billion citrus industry said Monday that a disease that was killing orchards worldwide was now rooted in Mexico, and experts warned that it was headed toward the state.

Citrus greening disease has infected six citrus trees on Mexico's Yucatan Peninsula, spread by an infestation of the Asian citrus psyllid.

There's a virtual insect highway across the width of Mexico, and once the aphid-like insect hops on, California is in trouble, said Beth Grafton-Cardwell, a UC Riverside entomologist and director of the Lindcove Research and Extension Center, east of Visalia.

Mexico "is infested with the bug and they will gradually move the disease across the country," Grafton-Cardwell said. "This disease is a citrus grower's worst nightmare."

U.S. and Mexican authorities are working together on solutions. In June, officials from the two countries as well as Belize met to discuss the severity of the infestations and ways to wipe to it out. They will meet again next month.

U.S. officials credited homeowners and growers for many of the insect discoveries so far, and urged them to remain alert.

Farmers shared their concern.

"This is an existential threat. It would put us out of business," said Jim Churchill, a Pixie tangerine grower in Ojai.

The disease doesn't affect humans, but it's lethal to citrus trees. It ruins the taste of fruit and juice before killing the plants, experts said, and there is no known way to rid a region of the pathogen once it has struck.

The disease has killed tens of thousands of acres of trees in Florida and threatens to put the Sunshine State out of the orange juice business, according to the state's Department of Citrus.

Since its discovery in Florida in 2005, the disease has quickly spread to every citrus-growing county in the state, contributing to the death of about 5% of its trees every year. It has wiped out much of the citrus industries in China, India, Saudi Arabia and Egypt, and has ravaged parts of Brazil.

How long California's citrus industry has before it too is afflicted by the disease is anybody's guess, Grafton-Cardwell said. Also called Huanglongbing, or HLB, the disease could take years to reach the state, but it could arrive far sooner if someone helps it along by bringing an infected plant across the border.

California's citrus industry already is on high alert.

Small colonies of psyllids from Tijuana have established themselves in San Diego and Imperial counties. But none of the psyllids trapped in those colonies turned out to be carriers of Huanglongbing disease. It was a lucky break, said Ted Batkin, president of the Citrus Research Board in Visalia.

What inspectors fear is the kind of citrus Armageddon that occurred in Florida, where officials surmised an uninfected psyllid fed on a diseased plant and flew to nearby citrus trees, spreading the disease. Other psyllids fed on the newly infected plants, distributing the pathogen throughout Florida.

An alternative source of infection could come from a psyllid carrying the disease hitchhiking in from overseas and starting the disease in California.

California had an exceptionally close call last month. Only the smart work of Chelsea, a Labrador retriever that sniffs out contraband plant material, kept diseased psyllids from escaping into some of the state's prime citrus-growing areas.

While working with agricultural inspectors at a FedEx depot in Fresno, Chelsea pointed to a duffel bag that had arrived from India. A plastic bag of curry leaves inside the duffel contained one dead adult psyllid and nine live juvenile insects, or nymphs. Tests subsequently found that nymphs were infected with Huanglongbing.

"The nymphs were put in alcohol and sent to the state lab in Sacramento for testing. We burned the curry leaves in case we didn't get all the bugs," said Tye Hafner, Fresno County's deputy agricultural commissioner.

Hafner said the duffel bag belonged to an older woman from India who was visiting her daughter in Fresno. The woman's luggage was lost in transit. The airline found the duffel and was delivering it to the woman at her daughter's home via FedEx when it was intercepted by Chelsea and the inspectors.

California caught a lucky break when the traveler got separated from her luggage, Hafner said. The curry leaves might have escaped detection in customs.

"Something like this wouldn't show up on an X-ray machine," Hafner said.

Chelsea regularly patrols the local shipping facilities. "When they do their sorts, Chelsea sniffs the packages as they go by and is trained to identify the ones that contain plant material," Hafner said.

Just to be careful, officials have set up traps in Fresno to make sure the infestation was contained to the bag of curry leaves.

"We are fairly confident that we intercepted the disease before it was released into the environment," Hafner said.

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