Application Timing Recommendations
- Observing persistent calyces at the end of the season should trigger scouting for postbloom fruit drop (PFD) symptoms on early bloom.
- Groves with a history of PFD should be scouted twice weekly.
- If PFD is seen on early bloom, fungicide application recommendations should be followed for the major bloom.
- Use the Citrus Advisory System (CAS) to help decide when to apply fungicides.
- Low-lying areas with frequent fog may need an application when the risk is just under the moderate threshold because of the lengthy wetting periods.
Fungicide Mode of Action Availability
Ferbam is no longer registered as of 2025. With the loss of the Ferbam registration, there is no longer a non-strobilurin-containing fungicide with efficacy against PFD available. Copper is ineffective for PFD management, so there are no multisite fungicides to recommend. This means that limiting fungicide use to only when necessary is very important for PFD. Use CAS for determining if an application is needed. We have not seen strobilurin (FRAC MOA 11) resistance yet, but it is still a concern, particularly because it is not possible to rotate to another mode of action.
Recommended Chemical Controls
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Rates for pesticides are given as the maximum amount required to treat mature citrus trees unless otherwise noted. To treat smaller trees with commercial application equipment — including handguns — mix the per-acre rate for mature trees in 125 gal of water. Calibrate and arrange nozzles to deliver thorough distribution, and treat as many acres as this volume of spray allows.
Table 1. Recommended chemical controls for postbloom fruit drop.