Dogs sniff out citrus tree disease

Ventura County is first to use detector dogs to identify trees with bacteria that causes HLB

By Kevin Hecteman

California Farm Bureau

VENTURA COUNTY – Using detector dogs as an early-warning system for a deadly citrus disease, Ventura County farmers have begun removing more than 200 trees after the dogs alerted them to the presence of the bacteria that cause the disease.

Huanglongbing—also known as HLB or citrus greening—has been found in residential citrus trees in Southern California but has not yet been detected in a commercial California grove. The disease has damaged and killed trees in Florida and other citrus-growing regions.

During the summer, the Farm Bureau of Ventura County hired a Florida-based company, F1K9, to bring four of its detector dogs to check some of the county’s citrus farms. The dogs are trained to find HLB bacteria.

“And they found it,” county Farm Bureau CEO John Krist said. “It wasn’t like they hit solid blocks of completely infected trees, but we had them run perimeters because that’s the most likely place that HLB will start when it reaches a grove.”

The dogs alerted on 211 trees out of 3,500 scouted, Krist said, and the affected trees are being removed.

“We’ve known that it was out there, but we had no way of really finding it until we were able to bring the dogs out here,” he said.

HLB is spread by an insect, the Asian citrus psyllid, and was first detected in the state in August 2008.

“Ventura’s had pretty hefty levels of psyllids for at least, I would say, five years and no known disease,” said Beth Grafton-Cardwell of the University of California Lindcove Research and Extension Center in Exeter.

Psyllid and HLB infestations usually start in urban areas and spread from there, she added.

The dog tests were carried out along the edges of groves because, before tarping regulations took hold, the psyllids might have hitched rides on citrus shipments from infested areas, Grafton-Cardwell said.

“They did see a fair number of alerts along those traffic corridors,” she noted. “That tells us that if the dogs are right, the bacteria have been there. Now, whether it’s causing infection in the trees or not, no way of knowing for several years.”

The canine-detection method is not yet officially validated by the California Department of Food and Agriculture or the U.S. Department of Agriculture. At present, the only USDA-approved method for confirming the presence of HLB is a DNA test called polymerase chain reaction, or PCR; a quarantine is imposed if the PCR test comes back positive.

Krist said the dogs came in because he doesn’t think Ventura citrus growers could wait for the length of time those tests require.

“We feel it’s the only chance we have to be out in front of the epidemic,” he said.

No quarantines will be triggered as a result of the canine visits, said Victoria Hornbaker, director of the CDFA Citrus Pest and Disease Prevention Program.

Hornbaker said she’s on board with whatever anti-HLB measures farmers take.

“Growers should be encouraged to use whatever (early detection methods) they feel comfortable with to make decisions on their own groves,” she said. “Regardless of regulatory involvement, we support that.”

The Ventura County growers who agreed to a detector-dog visit paid for it, at a rate of $4.50 per tree, and also agreed to remove any trees the dogs alerted on, Krist said.

“Right now, this is a voluntary program,” he said. “We believe that the dogs are sensing HLB. The growers we’re working with accept that.”

The dogs will return, he added, with the objective of canvassing the entire county.

“We’re hoping that this early removal of infected trees, at this early stage in the infection, will enable us to be out in front and keep it from taking hold in our groves,” Krist said.

The Florida-based detector dogs were trained in a program funded by a USDA grant and run by Tim Gottwald at the USDA research station in Fort Pierce, Florida. Grafton-Cardwell noted the dogs were trained to distinguish HLB from other diseases, such as Phytophthora—and that detection of HLB bacteria is not necessarily a death sentence.

“When a psyllid lays down some bacteria, it doesn’t always turn into an infection,” she said. “Sometimes the bacteria just sit there, so the dogs are able to detect the bacteria, but the tree may or may not be becoming diseased. And it takes, sometimes, several years for the bacteria to spread throughout the tree.”

Grafton-Cardwell said although some people want to see more proof of the dogs’ abilities to find HLB, others say they need to be used because citrus farmers along travel corridors know they’re at risk.

“Basically, they’re saying, let’s take the most conservative route, which would be remove trees, control psyllids,” she said. “And that’s all we can do to prevent disease spread at the moment, because we don’t have a cure for the disease.”

Research into citrus varieties that can resist or tolerate HLB continues, especially in Florida, said Melinda Klein, chief research scientist for the Citrus Research Board in Visalia.

“They’re more interested in tolerant varieties in Florida, relative to California, just because the disease is endemic in Florida,” Klein said. “We’d like to have resistant varieties, but we’ll take tolerant varieties, too, if it comes to it, in order to produce quality California citrus.”

Ben Faber, a subtropical horticulture farm advisor for UC Cooperative Extension in Ventura County, noted the distinction between the two—a tolerant variety can put up with the disease and produce a crop, whereas the resistant variety won’t get sick in the first place.

Later this month, a Bio-Safety Level 3 Laboratory for HLB Research will open in Riverside.

“We expect a lot of research to be going on, including in-state testing of California varieties under HLB conditions,” Klein said.

-Kevin Hecteman is an assistant editor of Ag Alert. He may be contacted at [email protected].

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