Research into gibberellic acid treatments for Hamlin oranges by UF/IFAS appears to have similar promising results to Valencias.
Gibberellic acid treatments have been shown to be successful in helping Valencia oranges deal with the effects of citrus greening. A Citrus Industry article maintains, “Monthly application of GA (September to January) on Valencia improved yield on average by 30%, reduced fruit drop and elicited enhanced plant defense response.” However, Hamlins have not undergone the same research “due to a shorter fruit-growth period (as compared to Valencia) and the need to stop GA application by October or November to allow sufficient time for color/Brix development,” according to the article. The article shared information on a new field trial using gibberellic acid on Hamlin oranges. See the details of the promising research below.
Gibberellic Acid Treatments
In the new trial, a 10-acre block of Hamlin trees received two applications of gibberellic acid (GA) about a month apart while the adjacent 10-acre block received no treatment as a control. Results of the gibberellic acid treatments field trial, from the article, include:
- The GA-treated Hamlin trees showed higher fruit detachment force (FDF).
- The GA-treated Hamlin trees showed less abscission (the physiological process of fruit separation).
- During a later ethylene-spray demonstration to simulate a stress situation on the trees, the GA-treated trees dropped 30 percent less fruit than the control trees.
- The Brix in untreated and GA-treated trees is similar with a marginal difference in fruit color.
The field trial has not yet included harvesting; it is planned for at least two years to collect enough data for recommendations.
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