Growing Citrus Trees With Oak Mulch

Ernie NeffHLB Management

Lukas Hallman

Lukas Hallman, a graduate student at the Indian River Research and Education Center (IRREC), is doing research to find what is in oak trees that apparently helps citrus cope with HLB. The University of Florida Institute of Food and Agricultural Sciences operates the IRREC.

“Anecdotal reports from Florida growers claim that citrus trees growing within the drip line of large oak trees have minimal HLB symptoms, while trees nearby, but not under the oak drip line, show severe symptoms,” said Hallman. He believes oak trees may hold a compound that boosts the citrus trees’ ability to tolerate the disease.

Marco Pitino, a former University of Florida postdoctoral researcher, published the first research study for oak tree extract used in the greenhouse against the bacterium that causes HLB. The work took place at IRREC. Pitino found the extract improved citrus trees’ ability to tolerate HLB in the greenhouse.

Hallman said a literature review and Pitino’s greenhouse study “were enough to form a viable hypothesis for a field study with oak mulch beds under citrus trees. Pitino’s work took place in a greenhouse. His findings need field tests.” 

Lorenzo Rossi, assistant professor of plant root biology at IRREC, is Hallman’s graduate research advisor. Rossi persuaded Hallman to apply for a Southern Sustainable Agriculture Research and Environment (SSARE) graduate student grant to fund research of his hypothesis.

When Hallman began to write the SSARE grant, a large oak tree fell on the IRREC property in a 2019 hurricane. In collaboration with U.S. Department of Agriculture (USDA) scientist Robert Shatters, Rossi and Hallman prepared the tree for mulch. The researchers used it for a bed under citrus trees in a research grove. With the research infrastructure in place, Hallman began to take monthly data from the root rhizosphere under the oak-mulched citrus tree beds.

“The oak mulch is easier to apply to trees than the oak extract,” said Rossi. “Through the research, we may find oak mulch soil amendments improve the soil and that the compounds in the mulch help citrus trees tolerate HLB.”

“In the future, we will need to identify which compounds are beneficial, where those compounds are in the trees, which oak species hold the specific compounds, and how much of the right compounds will control the disease,” Rossi said.

One year into the project, Hallman said he found more nutrients in the root rhizosphere. Also, preliminary findings show that as the mulch breaks down, soil biodiversity increases. 

“The research is a collaboration with the USDA,” Rossi noted.

Learn more about the research.

Source: University of Florida Institute of Food and Agricultural Sciences


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