Zero Tolerance For Citrus Disease

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The state of California will institute a policy of mandatory removal if any citrus trees in the state are found to be infected with the deadly disease Huanglongbing (HLB). An official with the state’s Department of Food and Agriculture (CDFA) announced the official policy at the 2012 Citrus Showcase, the annual meeting of California Citrus Mutual.

If any tree is found to be infected with HLB, the state will mandate its removal, no matter if it’s found in a commercial grove or in a residential back yard, Robert Leavitt, acting director for CDFA’s Plant Health and Pest Prevention Services, told the audience at the Visalia Convention Center. In Florida, where the disease has cost $3.6 billion and 6,600 jobs, Leavitt said officials waited too late, and California will not make the same mistake. “CDFA is committed to working with the industry to fight HLB tree by tree, street by street, and grove by grove,” he vowed.

In addition, in an attempt to prevent spread of the disease, the CDFA will try to eliminate the pest that carries HLB, the Asian citrus psyllid (ACP). Before any infected tree is pulled, CDFA will order a mandatory pesticide application to both the tree and the area around the tree to a minimum distance of 400 meters, said Leavitt. Many products can be used on ACP. A typical application would be a foliar pyrethroid spray and a ground application of imidacloprid, said Brian Taylor, field program director of the Citrus Research Board, at an afternoon workshop.

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Citrus industry members are understandably uneasy about HLB, because in virtually all other parts of the world where ACP was found, HLB followed. In Brazil, for example, 12 million trees have been pulled because of HLB, said the president of California Citrus Mutual, Joel Nelsen. It was found there and in Florida in 2005, and more recently has been found in Mexico and Texas. In general, said Leavitt, HLB has been found about five years after ACP invades. “We’re hoping to break that historical cycle,” he said. “There’s a high level of guarded confidence; there’s no panic.”

The reason he’s relatively confident is that they’ve been able to keep ACP out of heart of the California’s citrus industry — the famed San Joaquin Valley Citrus Belt, which lies along the foothills of the Sierra Nevada Mountain Range. ACP was first discovered in large numbers in east Los Angeles around Dodger Stadium, and officials have mostly limited ACP to a 640-square-mile quarantine in that area.

They’ve put out about 20,000 traps in that area, and so far have made nearly 73,000 residential treatments, said Nick Hill, the chairman of the California Citrus Disease & Prevention Program. The overwhelming majority of ACP have been found in residential areas, not commercial groves, said Leavitt.

They have encountered virtually no resistance from residents to the treatment program, which is funded entirely by commercial growers through a 9¢-per-box assessment that funds the California Citrus Pest and Disease Prevention Committee. “Most homeowners not only allow us (to spray), they welcome us because they get free insect control,” said Leavitt.

However, it might be a different story if HLB does turn up and the CDFA begins pulling trees. In Florida, when the state began pulling trees from people’s yards, state officials were met with resistance and instituted a compensation program. Leavitt said they were looking into the issue of homeowner compensation, and that was still to be determined. “We don’t expect any problems,” he said.

Taking (Bio)Control

Most recently, the state has started a biocontrol program. In December, University of California (UC)-Riverside scientists began releasing Tamarixia radiata — tiny, stingless parasitic wasps that lay eggs in ACP nymphs. Richard Stouthamer, UC-Riverside entomologist, said they are continuing to breed and release the wasps, and that by the end of May they expect they will produce 5,000 of the parisitoids per week.

Scientists are concerned that their attempt at biocontrol won’t work if there is too much inbreeding by the wasps, said Stouthamer, because inbreeding can produce wasps that aren’t as hungry for ACP as those found in the wild. For that reason, his UC-Riverside colleague, Mark Hoddle, has recently returned to Pakistan, where he originally located the wasps. Hoddle will collect more wasps from the wild and bring them back in an effort to increase the diversity of the California population.

It’s difficult to predict how successful biocontrol efforts will be in reducing ACP populations, said Stouthamer. “We’re still trying to determine how many wasps per tree need to be released to avoid releasing too few or too many,” he said.

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