Gibberellic Acid Continues to Show Benefits

Researcher Tripti Vashisth has been telling citrus growers about the benefits of using gibberellic acid (GA) on citrus trees. At the Citrus & Specialty Crop Expo, the University of Florida Institute of Food and Agricultural Sciences horticulturist said GA continues to show efficacy, based on 2022 harvest numbers.

Vashisth’s Expo presentation included details from a 2016–2022 study of 10-year-old Valencia orange trees on Swingle rootstock. Trees were treated monthly with GA from September to January. She reported:

• GA-treated trees dropped less fruit.
• There was significant canopy growth on GA-treated trees.
• GA increased fruit yields. GA-treated trees had higher yields in all six seasons. The highest GA yield of 282 pounds of fruit per tree came in 2018–19. Yield on control trees was 209 pounds of fruit per tree that season.
• Trees treated with multiple GA applications produced more fruit.

The researcher also reported that GA reduces the number of flowers, enhances leaf and fruit growth and improves tree defense responses, among other benefits. She emphasized that the timing of GA applications and repeated applications are the keys to best results.

In Vashisth’s studies, the five-year average for fruit drop was lowest at 18% when trees were treated five times with GA from September to January. The five-year average fruit drop was:

• 23% with four applications from September to December
• 25% with three applications from September to November
• 23% with two applications from September to October
• 27% in a control without GA applications

Fruit drop has become one of the primary reasons Florida growers have experienced drastic yield reductions since HLB became widespread in the state.

Combining gibberellic acid and 2,4-D applications was also promising, Vashisth told the Citrus Expo audience. Learn more about the GA plus 2,4-D studies from another presentation Vashisth made after Expo.

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