Dangerous Avocado Pathogen Grows Faster in Cooler Temperatures

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Avocados growing on a tree. Avocado fruit. UF/IFAS Photo by Tyler Jones.

By: Brad Buck, 352-294-3303, bradbuck@ufl.edu

GAINESVILLE, Fla. — A University of Florida scientist has some new data that avocado growers might consider: The disease grows faster in the fall or winter than in the summer, so growers may want to look for laurel wilt more closely during the winter.

Laurel wilt has been ravaging Florida’s avocadoes, which have a University of Florida/Institute of Food and Agricultural Sciences (UF/IFAS)-estimated $100 million-a-year economic impact on the state. UF/IFAS scientists say several species of ambrosia beetles transmit laurel wilt to avocado trees.

But growers – nearly all of whom are in Miami-Dade County — may consider scouting for laurel wilt during cooler temperatures (e.g. October to March), said Nemat Keyhani, professor of microbiology and cell science at UF/IFAS. They may also want to change how they eliminate wilted branches so they don’t leave contaminated trees in the area next to healthy trees, as the fungus can spread rapidly as temperatures cool, Keyhani said.

Keyhani grew laurel wilt at different temperatures in his lab on the UF Gainesville campus. Though his data are preliminary, Keyhani said the pathogen, known scientifically as Raffaelea lauricola, grows best between 68 and 79 degrees F, but it barely grows between 86 and 89 degrees F, Keyhani said.

When growers see their trees wilting, many cut affected branches down, potentially giving them a false sense of security that the disease is gone, he said. It’s likely still lingering and growing slowly or dormant in the tree, waiting for the right growing temperature, Keyhani said.

“For growers, as a tree presents symptoms, cutting of wilted branches may temporarily result in little to no infection of the rest of the tree during hotter months,” Keyhani said. “Sometimes that works, and they don’t see the spread of the disease, and they say, ‘OK, things are great.’ But what happens is that, for some reason, the disease will come back after a few months.”

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