Research Results Into Plant Growth Regulators for Preharvest Fruit Drop

Explore the results of UF/IFAS research that studied if plant growth regulators can reduce preharvest fruit drop.

A UF/IFAS Tip of the Week article started “Preharvest fruit drop is a major concern for Florida citrus growers, especially in groves affected by huanglongbing (HLB).” The article also shared that “Environmental stressors such as drought, flooding and cold snaps further accelerate fruit drop and tree decline.” The article examined recent research into using plant growth regulators (PGRs) to combat preharvest fruit drop. See the details on the research results below.

The Plant Growth Regulators

The article shared that two different plant growth regulators (PGRs) were used, gibberellic acid (GA3) and 2,4-D, in the research to use RGPs to reduce fruit drop. The article maintained that “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 Study

The research involved field trials in Central Florida studied the efficacy of the PGRs in reducing “fruit drop in mature Valencia sweet orange trees.” The article maintained that “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”

Research Results

The article shared that the field trials had the following 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.”

The research advised that “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.” It also added that “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.”

Griffin Fertilizer is committed to helping both growers and ranchers make sound agronomic and economic decisions in order to maximize the health of their grove and pasture. As a full-service custom dry & liquid fertilizer blender and crop protection product distributor, we will continue our mission to further advance Florida agriculture. For questions or concerns about your farm or pasture, contact us and one of our team will be in touch.  

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