By Tripti Vashisth, Maricielo Postillos and Taylor Livingston
In recent years, many citrus growers in Florida have begun using gibberellic acid (GA) to enhance tree growth and productivity. Initially, the recommendation was to apply GA monthly from September to January for Valencia oranges to maintain canopy health, reduce fruit drop and improve yields. However, some growers are hesitant about applying GA in the fall due to concerns about the greener peel color, which can affect the appeal of fresh fruit even though GA does not impact internal quality. Additionally, applying GA five times increases production costs.
Recent field trials have investigated the effectiveness of applying GA in early summer and the minimum number of applications needed to optimize tree productivity. Data collected over two years for both Hamlin and Valencia oranges showed that trees receiving three or more GA sprays exhibited better fruit retention and lower preharvest fruit drop compared to untreated trees. While untreated trees experienced a decline in canopy density, those treated with GA maintained a more stable canopy, with better results for trees receiving more applications. Notably, even after Hurricane Milton, the treated trees preserved their canopies.
Overall, the yield improved by 30% with a higher number of GA applications. In terms of fruit quality, internal traits such as Brix, acidity percentage and pounds of solids per box were not significantly affected by the number of GA sprays in either Hamlin or Valencia oranges. However, peel integrity improved, indicated by lower electrolyte leakage, even though the color development of treated fruit was slightly delayed. It is important to note that applying GA three to five times resulted in a greener peel color.
The research results suggest that early and repeated GA applications can be a valuable strategy for growers managing groves affected by HLB (citrus greening disease). A minimum of three applications, spaced 45 days apart starting in July, can promote canopy health and reduce fruit loss without compromising the internal fruit quality.
Tripti Vashisth is associate center director and an associate professor, Maricielo Postillos is a visiting scholar, and Taylor Livingston is a biological scientist — all at the University of Florida Institute of Food and Agricultural Sciences Citrus Research and Education Center in Lake Alfred.
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