By Megan Dewdney
Despite being in a transition from a La Niña to a neutral El Niño Southern Oscillation phase, Florida has not had warmer than average temperatures in the last two weeks from March 3. Looking at historical trends, temperatures for the last two weeks of February were in the normal range for this time of year.
When looking at the precipitation situation, locations are very different. In Central Florida and the Indian River, rainfall is just below the average yearly accumulation, but in the Southwest, there is a rainfall deficit of nearly 2 inches.
With all the cool weather and in some cases, water deficit, citrus trees are primed to flower in a synchronized manner. For the predicted timing in your area, follow the flower bud advisories. In North Central and Central Florida, flowering is expected to occur in the first and second weeks of March. Much of this period is predicted to be dry, with warm days and cool nights. These are good conditions for humans, but not great conditions for postbloom fruit drop (PFD).
There is a prediction of rain in Central Florida in the first week of March after warmer weather with lows in the 60s. Since this rain is associated with cooler weather, a PFD infection period seems unlikely unless the conditions are wet for a long period of time. What might transpire when bloom is at its peak in Southwest Florida and Indian River is too far away to make any predictions now, but keep an eye on warm, wet weather predictions.
Because weather can be very local, it is important to be monitoring for PFD disease risks even though the likelihood of disease seems low this year. Blocks with chronic problems may be at just enough risk with the upcoming rain events during bloom to see disease. Monitor the disease risk in your area with the Citrus Advisory System. As a reminder, if a block is located in an area where there are longer wetting periods than your Florida Automated Weather Network station, add up to 0.05 to the infection index to see if you cross the threshold for disease. These locations include low-lying areas prone to fog or near waterbodies.
There are limited fungicide choices for PFD. Only the strobilurin (FRAC 11) fungicides have been consistently effective in University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) trials. But these fungicides are prone to resistance development so they should be used sparingly. There is a label limit of four applications within a growing season. Consult the Florida Citrus Production Guide for specific information on fungicides and timing to manage PFD.
Megan Dewdney is an associate professor at the UF/IFAS Citrus Research and Education Center in Lake Alfred.
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