A strangler is stalking the avocado trees of South Florida, threatening backyard trees as well as thousands of acres of commercial groves.
Laurel wilt disease has turned up in Palm Beach and Miami-Dade counties, and experts say it will almost certainly reach Broward County. The disease swiftly chokes the life from trees in the laurel family by destroying their tubular systems for transporting water and nutrients. The trees include redbay, swamp bay and avocado.
The disease, carried by a beetle smaller than a grain of rice, was discovered February in redbay trees at the Loxahatchee National Wildlife Refuge in Palm Beach County. This week, the Florida Department of Agriculture announced it had been discovered in an avocado grove in southern Miami-Dade County, home to the second largest avocado crop in the United States.
"The find of laurel wilt in a commercial avocado grove is a major concern," said Agriculture Commissioner Adam Putnam. "Unaddressed, the disease can spread quickly, threatening the health of South Florida's commercial avocado industry. We're working with our partners and the industry to diagnose other trees in proximity to the finding and mitigate the spread of the disease."
Authorities are asking people to keep on eye on their trees and report any signs of the disease: sudden leaf wilt, quick death and darkened, brownish wood. They say the disease likely spreads through the transport of firewood and ask that people use only local firewood.
Scientists have begun helicopter surveys of southern Miami-Dade County; any diseased commercial trees will be destroyed.
Jonathan Crane, professor of agriculture at the University of Florida, who is involved in the fight, said scientists have several weapons against the disease, including insecticides, fungicides, barriers, repellents, and trap-and-kill systems. But none have been shown to work decisively.
"We have not found a magic bullet," he said.
Denise Feiber, spokeswoman for the Florida Department of Agriculture, said, "It's a very challenging disease. There's nothing that's tried and true."
In the agricultural lands around Homestead, 6,773 acres are devoted to avocados, accounting for nearly $13 million in sales. At Brooks Tropical, the largest commercial avocado operation in the region, president Neal Brooks said he takes the discovery seriously but doesn't think it threatens the industry in South Florida.
"I am not in a position to panic," he said. " I am hopeful we will continue to find results from research to stop the bug or stop the spread. Whatever spread occurs, I would expect it to be relatively slow, and we will monitor it as it goes along."
The disease is spread by the redbay ambrosia beetle, an insect suspected of arriving in the United States at the port of Savannah, possibly in packing pallets or crates. The beetle bores into the tree's trunk and spreads the laurel wilt fungus. As the tree starts to die, additional beetles bore in and lay eggs, with the newly hatched larvae feeding on the fungus that now lines the tree's insides.
With the disease in Palm Beach County and Miami-Dade County, Crane said there's little doubt it will eventually arrive in Broward.
At Spyke's Grove, a nursery that has operated in Davie since 1950, the 16 varieties of avocado tree for sale are among the most popular items.
"We sell a lot of them," said Barbara Granger, the owner. "We sell mostly citrus, then mango, then avocado.''
Having dealt with citrus canker, citrus greening and various other plant ailments, she said disease was a part of life for people in the nursery business and expressed confidence that scientists would be able to deal with this one.
"There are a lot of diseases for all of the different trees out there," she said. "They really are coming up with good ideas for handling them."