Citrus Advisory System May Help Prevent Losses From Postbloom Fruit Drop

GAINESVILLE, Fla. — A new University of Florida-developed forecasting system could help citrus growers control postbloom fruit drop this winter, despite the predicted El Niño weather pattern that’s expected to bring more rain and moderate temperatures.

With an El Niño, forecasters expect above-average rain this winter and early spring. Increased rain improves the chances of fungal spores splashing from flower to flower in citrus groves, researchers with the UF Institute of Food and Agricultural Sciences say. Those fungal spores cause a disease known as postbloom fruit drop (PFD).

PFD causes citrus fruit to fall off a just after flowering, said Megan Dewdney, a UF/IFAS associate professor of plant pathology. After the fruit falls, it leaves behind a “button” on the tree – the part of the tree to which the fruit would normally be attached.

Dewdney, a faculty member at the UF/IFAS Citrus Research and Education Center in Lake Alfred, Florida, works with Natalia Peres, professor of plant pathology at the UF/IFAS Gulf Coast Research and Education Center in Balm, Florida, and Clyde Fraisse, a UF/IFAS professor of agricultural and biological engineering on a web tool to help growers control PFD.

The system helps growers know the most appropriate times to spray fungicides on their citrus trees to minimize PFD. Following feedback from growers, the UF/IFAS researchers developed a new Citrus Advisory System with less information required to be entered into the model and adding visual forecasts.

“The system allows growers to receive forecast alerts to their phones of infections for areas of citrus trees they consider important,” Dewdney said. The mobile technology is based on weather data from the UF/IFAS-developed Florida Automated Weather Network.

PFD can appear explosively in a bad season, seemingly infecting every flower on a tree, Dewdney said. It can cause between 20 percent and 80 percent yield loss, depending on the severity of the conditions, she said.

As part of the research team’s continuing work on PFD, a graduate student, André Bueno Gama, is working on ways to further improve predictions. Gama is studying historical weather data and experiments to expand scientists’ understanding of the fungus’ biology so researchers can better see how the fungus grows.

Researchers also are testing chemical treatments for their efficacy against the fungus, and they’re evaluating fungicide programs for disease management.

The research, funded by the Citrus Research and Development Foundation, will give growers the information they need to rotate fungicides so they’re not using a treatment for which the fungicide has developed resistance.

“We need to know which fungicides work well together for adequate control,” Dewdney said. “The fungicides prevent the flower petals from becoming infected but cannot prevent the loss of the small fruit of an already infected flower.”

To access the Citrus Advisory System, click on the AgroClimate platform, and go to the “tools” section.


By: Brad Buck, 352-294-3303,

The mission of the University of Florida Institute of Food and Agricultural Sciences is to develop knowledge relevant to agricultural, human and natural resources and to make that knowledge available to sustain and enhance the quality of human life. With more than a dozen research facilities, 67 county Extension offices, and award-winning students and faculty in the UF College of Agricultural and Life Sciences, UF/IFAS works to bring science-based solutions to the state’s agricultural and natural resources industries, and all Florida residents. Visit the UF/IFAS web site at and follow us on social media at @UF_IFAS.




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Posted: November 7, 2018

Category: UF/IFAS
Tags: Agricultural And Biological Engineering, Citrus Advisory System, Citrus Research, Citrus Research And Development Foundation, Citrus Research And Education Center, Clyde Fraisse, Department Of Plant Pathology, Megan Dewdney, Natalia Peres, News, Postbloom Fruit Drop

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