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Florida avocado industry faces pressure from tree disease

Tree growers and researchers across Florida continue to try to reduce the damage caused by a decades-old disease that is impacting avocado production.

The disease, known as laurel wilt, was first introduced to the United States through infested wood packaging material from Asia in 2002, according to the Institute of Agricultural and Food Sciences at the University of Florida.

“A ship arrived in Port Wentworth, Georgia, with some wooden pallets,” said Jeff Wasielewski, UF/IFAS Extension tropical fruit business agent for Miami-Dade County. “Inside these wooden pallets were very small ambrosia beetles and they were carrying a fungus.”

Laurel wilt is spread naturally by beetles, which commonly inhabit avocado orchards. The mushroom, Raffaelea lauricolacauses rapid deterioration of older avocado trees.

“The fungus actually reaches the center of the tree,” Wasielewski said. “And the center of an avocado (tree) is where the water rises. So the fungus is there and the tree blocks it because the tree is trying to stop the fungus. But the fungus is so aggressive that the tree overreacts and blocks its own water supply, and then wilts.”

In South Florida, the disease has caused the loss of more than 300,000 trees in an industry worth an estimated $54 million.

The rapid spread of the pathogen within groves, as well as among residential trees, makes finding a solution difficult.

“I think in the beginning there were a lot of groves that weren’t being managed,” Wasielewski said. “So (the avocado trees) were very overgrown with vines and big canopies. In a way, they were wiped out because people weren’t aggressively controlling the disease.”

Ragweed beetles carry the fungus that causes laurel wilt, which affects the family of trees from which avocados come.

Ragweed beetles carry the fungus that causes laurel wilt, which affects the family of trees from which avocados come.

The damage caused by bay leaf wilt is comparable to other diseases in fruit production throughout the state, such as citrus greening, which has affected Florida’s citrus industry.

“It’s one of the worst,” Wasielewski said. “The greening of citrus fruits and the wilting of laurel, I would put them quite close together. Citrus greening gets more press because, obviously, oranges are our state fruit. But laurel wilting is also a death sentence. “Once it gets into the tree, you won’t be able to get it out.”

Despite the difficulties, researchers have been working closely with avocado growers to lessen the effects of laurel wilt on seasonal production.

“Remember that the disease entered the country in 2002; came to Miami-Dade County in 2011,” Wasielewski said. “Since then we have been studying the disease. We’ve been working on it, the University of Florida and other researchers as well. The producers have also found some things. “I think we are doing a good job and I don’t think this year will be worse than last.”

Much of the research on laurel wilt points to careful management of susceptible trees as the primary solution to its spread.

“As with any pest or disease, the first thing is to keep the trees very healthy,” Wasielewski said. “So you want them fertilized, you want them irrigated, you want them in top shape.”

Wasielewski also said growers should keep avocado-producing trees well pruned and open to light and air, as these conditions are less attractive to beetles.

“Researchers at the University of Florida did a study and found that ambrosia beetles prefer shade, since they come from a forest area,” Wasielewski said. “So if it’s too sunny, they don’t want to be there. A good pruning will take away a lot of (shade).”

And although laurel wilt may be a persistent problem, researchers believe conditions are not expected to worsen in coming seasons.

“It sounds bad, but the producers are doing the best they can,” Wasielewski said. “It’s not the end of the world. We are still producing our Florida avocados and we are still releasing a great product. I am very proud of the growers and the researchers.”

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