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Adult Diaprepes citrus weevil. Photo courtesy of U.S. Department of Agriculture/Agricultural Research Service. Click here for high-res image.

GAINESVILLE, Fla. — The Diaprepes citrus weevil is often more abundant in finely textured, poorly drained flatwoods soils than in the sandy soil varieties of Florida’s Central Ridge; perhaps that’s because sandy soils seem to host more species of nematodes that prey on insects.

Researchers with the University of Florida’s Institute of Food and Agricultural Science have taken those observations and turned them into a potential management technique, using “transplanted” soil and nematodes to grow flatwoods citrus. Their results appear in the January issue of the journal Biological Control.

In the study, researchers conducted experiments at a weevil-infested flatwoods citrus grove in Osceola County. They planted 50 trees in oversized holes filled with sand, and 50 trees in native soil, then introduced predatory nematodes to most of the trees. For the next four years, researchers monitored nematode and weevil populations and checked tree health.

The results showed there were more predatory nematodes of more species — and fewer weevils — in the root zones of trees planted in sandy soil. By the study’s end, 21 trees in native soil had died of weevil herbivory, compared with three trees in sandy soil. Surviving trees in sandy soil also had 60 percent greater trunk diameter and produced 85 percent more fruit than those in native soil.

Lead author Larry Duncan, a professor at UF’s Citrus Research and Education Center in Lake Alfred, said researchers are eager to learn how to keep transplanted nematode populations robust. In a future study they’ll plant the citrus trees in trenches rather than holes, because trenches should enable the microscopic creatures to travel from one root zone to another.

Once optimized, the system may catch on with flatwoods citrus growers, Duncan said. Some already plant their trees in sandy soil to achieve better drainage.

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Contacts

Writer: Tom Nordlie, 352-273-3567, tnordlie@ufl.edu

Source: Larry Duncan, 863-956-8821, lwduncan@ufl.edu

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University of Florida nematologist Larry Duncan (back row, center) poses with members of his laboratory: Entomologist Robin Stuart (back row, left); soil ecologist Fahiem El-Borai (back row, right); nematology doctoral student Ekta Pathak (front row, left); and nematode ecologist Raquel Campos-Herrera (front row, right).

All five were part of a research team that investigated a potential new management strategy to discourage Diaprepes citrus weevils in flatwoods citrus groves with finely textured soils. The team planted citrus trees in oversized holes that had been filled with sandy soils, and released predatory nematodes. The results suggest that nematodes thrived in the “transplanted” soil and dramatically reduced herbivory by the weevil, a major citrus pest. UF/IFAS photo by Katherine Snyder

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