Tree growers and researchers across Florida are continuing to try to reduce the harm caused by a decades-old disease that’s impacting avocado production.
The disease, known as laurel wilt, was first introduced to the United States through infested wood packing material from Asia in 2002, according to the University of Florida Institute of Food and Agricultural Sciences.
“A boat came into Port Wentworth, Georgia, with some wooden pallets,” said Jeff Wasielewski, a commercial tropical fruit agent at the UF/IFAS Extension Miami-Dade County. “Inside these wooden pallets were very tiny ambrosia beetles, and they were carrying a fungus.”
Laurel wilt spreads naturally via the beetles, which commonly inhabit avocado groves. The fungus, Raffaelea lauricola, causes a rapid deterioration of older avocado trees.
“The fungus actually gets into the center of the tree,” Wasielewski said. “And the center of an avocado [tree] is where the water goes up. So the fungus is in there, and it's getting blocked by the tree because the tree is trying to stop the fungus. But the fungus is so aggressive, the tree hyper-reacts and blocks its own water supply, and then you get that wilting.”
In South Florida, the disease has resulted in the loss of over 300,000 trees across an industry worth an estimated $54 million.
The rapid spread of the pathogen inside groves, as well as among residential trees, makes finding a solution difficult.
“I think early on, you had a lot of groves that weren't being managed,” Wasielewski said. "So [the avocado trees] were very overgrown with a lot of vines, big canopies. They kind of got wiped out because people weren't aggressively managing the disease.”
The damage caused by laurel wilt is comparable to other diseases in statewide fruit production, like citrus greening, which has plagued Florida's citrus industry.
“It's up there as one of the worst,” Wasielewski said. “Citrus greening and laurel wilt, I would put them pretty close together. Citrus greening gets more press because obviously, the oranges are our state fruit. But laurel wilt is also a death sentence. Once it gets in the tree, you're not going to pull that tree out of it.”
Despite the difficulties, researchers have been working closely with avocado growers to lessen the effects of laurel wilt on seasonal production.
“Remember, the disease came into the country in 2002; it got down to Miami-Dade County in 2011,” Wasielewski said. “Since then, we've been studying the disease. We've been working on it, the University of Florida, other researchers as well. The growers have found some things as well. I think we're doing a good job, and I don't think it's worse this year than in the past.”
Much of the research into laurel wilt points to carefully managing susceptible trees as the main solution to its spread.
“As with any pest or disease, number one, you want to keep your trees very healthy,” Wasielewski said. "So you want them fertilized, you want them irrigated, you want them at top shape.”
Wasielewski also said that growers should keep avocado-producing trees well-pruned and open to light and air, as these conditions are less attractive to beetles.
“The researchers at the University of Florida did a study and found that the ambrosia beetles prefer to be shaded, as they come from a forest area,” Wasielewski said. "So if it's very sunny, they don't want to be there. A good pruning will take away a lot of [shade].”
And while laurel wilt may be a persistent issue, researchers believe conditions are not expected to worsen in the coming seasons.
“It sounds bad, but the growers are doing the best they can," Wasielewski said. “It's not the end of the world. We're still putting out our Florida avocados, and we're still putting out a great product. I'm really proud of the growers and the researchers.”
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