Beetle, fungus threaten Florida's avocado industry

Scientists are tracking the redbay ambrosia beetle as it crisscrosses the southeastern United States, spreading a fungus that is killing avocado trees. The beetle and the fungus it transmits could be devastating in Florida, the country's second-largest avocado producer.

The fungus, called laurel wilt disease, has so far only affected the avocado trees of homeowners and has not yet infiltrated the industry's commercial growing hub in South Florida, said University of Florida plant pathologist Randy Ploetz.

It has already been recorded Okeechobee County, however, which is dangerously close to Miami-Dade County, where most of the state's 7,500 acres of commercial trees are planted.

"It has not reached us yet," Ploetz said, "but it's only 100 miles away."

About 60,000 Floridians have at least one avocado tree growing in their yards. Florida's avocado industry brings in about $30 million annually.

Florida trails only California, which has not yet been infiltrated by the pest, in avocado production nationwide. Under a rough estimate in which half of the state's commercial avocado trees died, it would mean a total economic impact of about $27 million, including lost jobs, said UF agricultural economist Gilly Evans.

"It could wipe out the entire industry," he said.

Evans estimated that about $250,000 had been spent on research, with scientists working to find a treatment that could slow the disease's spread. But possible pesticides or fungicides might present health risks or be too expensive for growers.

In Miami-Dade, there is little Craig Wheeling can do to protect his Homestead-based business. The CEO of Brooks Tropicals says the impending threat of laurel wilt disease bears a striking resemblance to citrus canker, which struck Florida orange and lime growers years ago, causing millions of dollars in damage.

"Having gone through that mess in the early 2000s, we're very concerned when we see the redbay ambrosia beetle coming down," he said.

Scientists believe the beetle is native to Asia and first came to the United States through a shipping port in Georgia. Laurel wilt was first documented in the U.S. in 2004 and has so far popped up in South Carolina, Georgia and Florida. The beetle naturally expands its range about 20 to 30 miles each year, but is also transported when the beetle's host tree is cut for firewood.

"When you're moving wood around and you have some redbay growing out there and you have some backyard avocados growing as well, you may be providing an easy pathway for that pest to move south," said Frank Koch, a researcher with the North Carolina State University who has projected the beetle and the disease it carries will hit South Florida around 2020 or sooner.

Laurel wilt is both difficult to identify and quickly attacks a tree, starting at its crown and working its way throughout the plant. Beetles that spread the fungus tend to attack healthy plants, scientists say, burrowing a tunnel in the wood then inoculating its walls with spores.

"What you're looking for is wilted stems as leaves, some black streaking in the wood. Strings of compacted sawdust that would be protruding primarily from tree trunks," state Department of Agriculture spokesman Mark Fagan said.

Of the 28 species of avocado grown in Florida, all are susceptible to the disease but not all have died, Fagan said. So far only homeowners have been affected, which has made it challenging for researchers to how the disease should be handled by commercial growers. Other types of redbay trees at risk include sassafras, camphor, silkbay, swampbay, pondspice and pondberry, which is an endangered species.

"Trying to predict what this thing is going to do has been difficult, because this is actually a brand new disease," Ploetz said. "We knew nothing about this before it showed up."

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On the Net:

University of Florida Institute of Food and Agricultural Sciences Extension, http://edis.ifas.ufl.edu/HS379

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