Reduce Post-Hurricane Fruit Drop With PGRs

By Tripti Vashisth and Taylor Livingston

Hurricane Milton passed over many citrus-producing counties in Florida, resulting in canopy and fruit loss (especially in early varieties). HLB-affected trees undergo a lot of stress, and now the hurricane has added more abiotic stress to trees. High-speed winds caused significant fruit and leaf drop. The fruit and leaves that escaped the drop during the hurricane are still quite likely to fall in subsequent days. Therefore, going forward, the goal is to retain as much fruit as possible and rejuvenate citrus trees for healthy vegetative growth.

2,4-D AND GIBBERELLIC ACID

For retaining fruit, use of 2,4-D and gibberellic acid (GA) is suggested. Both plant growth regulators (PGRs) have potential to improve fruit retention and counteract ethylene (the hormone that is known to cause leaf and fruit drop). In the past several years, University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) researchers have seen that GA application will improve fruit retention and canopy density of citrus trees. Grower-collaborated field trials evaluating the use of GA on HLB-affected Hamlin in Polk and Hardee counties from 2021 to 2023 have shown that the GA trees retained, on average, 50 pounds more fruit than the control trees — even after Hurricane Ian devasted the Hardee site.

Post-Hurricane Ian, UF/IFAS researchers had an opportunity to evaluate these PGRs for fruit drop mitigation. As a hurricane-recovery measure, 2,4-D was applied to a subset of GA-treated trees in Hardee County two weeks after Hurricane Ian. The treated trees retained 33.3 pounds more fruit (approximately 50% more) than control trees at harvest. The control trees lost 17% of their canopy while the GA trees only lost about 4%. Results show that the use of PGRs such as GA and 2,4-D may help the tree’s ability to mitigate HLB disease symptoms while also protecting against Florida’s unpredictable weather patterns. 

TAKE-HOME MESSAGES

GA applications on HLB-affected Hamlin increased yield and reduced fruit drop. 

GA applications mitigate negative response to abiotic factors such as hurricanes and hard freezes. 

Use of 2,4-D can reduce further fruit drop caused by damage from hurricanes. 

Tripti Vashisth is an associate professor, and Taylor Livingston is a biological scientist, both at the UF/IFAS Citrus Research and Education Center in Lake Alfred.

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