Florida orange

The Promise of Gibberellic Acid

Josh McGillHLB Management, PGRs

Researcher Tripti Vashisth shed additional light on the promise of gibberellic acid (GA) applications in rejuvenating HLB-affected orange trees during a Jan. 11 presentation. Some of the important messages that the University of Florida Institute of Food and Agricultural Sciences associate professor highlighted were:

gibberellic acid
  • GA application on Hamlin seems to be more promising than on Valencia.
  • GA-treated trees had significantly higher yield efficiency than untreated trees after two years of GA application. Yield efficiency is important because it accounts for canopy volume (fruit-bearing area) that may exist in trees before the start of experiments.
  • GA plus 2,4-D helped in reducing fruit drop after Hurricane Ian in September 2022.

In a 2016 to 2022 Valencia field trial, GA applications made from September to January resulted in more fruit. The GA-treated trees produced a 5-year average of 220 pounds of fruit per tree and 2.4 boxes per tree versus control trees that produced 172 pounds per tree and 1.9 boxes per tree. From that trial, Vashisth extrapolated that a block with 150 trees per acre treated with GA would have produced 367 boxes per acre, compared to 287 boxes per acre for untreated trees.

The GA in Valencias also resulted in more vegetative growth, larger fruit, lower fruit drop and overall tree health improvement. 

In a 2021 to 2022 Hamlin study, a grower sprayed half of several blocks with GA and left the control halves untreated.

At one site, the first-year yield for GA-treated trees was 310.5 pounds of fruit per tree versus the control’s 292.8 pounds. Yields dropped in the second year to 161.3 pounds per tree in the GA treatment versus 80 pounds in the control.

At a second site, the first-year yield for GA treatment (225.3 pounds per tree) trailed the control yield (302.8) pounds. In the second year, the GA treatment yield (167.4 pounds per tree) exceeded the control yield (156 pounds).

Vashisth said the reduction from the first year to the second year in both sites was possibly due to Hurricane Ian.

Learn more here about the benefits of gibberellic acid.

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