Dual-Action Approach to Mitigate Preharvest Fruit Drop

By Taylor Livingston and Tripti Vashisth

Preharvest fruit drop is a major concern for Florida citrus growers, especially in groves affected by huanglongbing (HLB). Environmental stressors such as drought, flooding and cold snaps further accelerate fruit drop and tree decline.

Recent field trials in Central Florida evaluated the use of plant growth regulators (PGRs) — specifically gibberellic acid (GA₃) and 2,4-D to reduce fruit drop in mature Valencia sweet orange trees. These PGRs are reported to work through different mechanisms: GA₃ helps maintain canopy and peel health, while 2,4-D slows the fruit’s natural abscission signal and counters ethylene, a hormone that promotes drop in HLB-affected trees. The two-year field trial evaluated four treatments on the same sets of trees:

1. Untreated control
2. Single November spray of 2,4-D (3.2 oz/acre)
3. Three smaller monthly sprays of 2,4-D (1 oz/acre) from September to November
4. Tank mix of 2,4-D (3.2 oz/acre) + GA₃ (10 oz/acre) in November

Key Results:

• Treatment 4 (2,4-D + GA₃) was the only treatment that consistently reduced fruit drop in both years.
• In Year 1, it reduced fruit drop by 16% compared to untreated trees.
• In Year 2, despite Hurricane Milton, it reduced fruit drop by ~15% and improved fruit yield and canopy productivity.
• Multiple small sprays of 2,4-D did not offer additional benefits over a single full-rate application.
• Addition of GA₃ to 2,4-D seems to provide an additive effect in reducing fruit drop.

To conclude, a single, well-timed November spray of 2,4-D combined with GA₃ is an effective and cost-efficient strategy to reduce fruit drop in HLB-affected citrus. This combination targets different hormonal pathways, improving fruit detachment force and reducing stress-related hormone levels in the peel.

This treatment may also help extend the harvest window. If growers are unable to harvest fruit immediately due to labor shortages, weather or other logistical issues, the reduced fruit drop from this treatment can help retain fruit on the tree longer, thus minimizing losses.

Growers are encouraged to consider this PGR strategy as part of their grove management, especially during the critical pre-harvest period. Continued research will help refine timing and dosage, but current evidence supports this method as a practical tool to protect yields and reduce economic losses. However, the GA application can result in green peel color retention, thus this may not be an applicable strategy for fresh fruit growers.

Tripti Vashisth is associate center director and associate professor, and Taylor Livingston is a biological scientist, both at the University of Florida Institute of Food and Agricultural Sciences Citrus Research and Education Center in Lake Alfred.