It’s Almost Time to Spray Gibberellic Acid

Josh McGill HLB Management, Tip of the Week

By Tripti Vashisth

Gibberellic acid (GA) can benefit citrus trees in many ways. GA can improve vegetative and fruit growth while reducing fruit drop and flowering intensity.

Evidence is mounting that repeated application of GA is needed to induce the desired positive effect on fruit growth and tree productivity. In a multiyear field trial on Valencia orange, monthly application of GA from September to January improved yield on average by 30%, reduced fruit drop and elicited enhanced plant defense response. The repeated monthly application of GA has been an important factor in improving productivity of Valencia trees.

Gibberellic Acid

Last year, a number of grower trials were initiated to gather information on use of GA on early- and late-maturing sweet orange varieties. The preliminary information on Hamlin is promising. The data suggest that in addition to applying GA sprays early in the season, three applications of GA were better than two applications. Growers who made the first GA application in late October or November on Hamlin trees did not see any significant benefit to fruit drop reduction or yield enhancement. The grower who saw the maximum benefit with GA application on Hamlin started the application at the end of August and carried the sprays to November. An early start to GA application benefits the growing fruit and can reduce fruit drop.

For growers who are planning to try out GA this year, this is a good time to start thinking about the sprays. The timing of GA application will depend on the variety and when you plan to harvest. It is ideal to have a two- to three-month gap between the last GA application and the anticipated harvest.

For example, for Hamlin, it is suggested to start the sprays in August and try to squeeze in at least three applications 30 to 45 days apart. It is best to not go beyond Nov. 15, as the harvest can be significantly delayed. One additional potential benefit of a November spray is flower suppression. By suppressing flowering, the source-to-sink ratio can be improved, thus improving next season’s fruit set and growth.

The bottom line is to have a plan! Feel free to contact Tripti Vashisth at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Citrus Research and Education Center (CREC) if you have question about GA applications.

UF/IFAS researchers are continuously working on gathering more information on GA application in different varieties and regions to develop solid recommendations. It is a slow process.

Read more on gibberellic acid research here.

Tripti Vashisth is an associate professor and citrus Extension specialist at the UF/IFAS CREC in Lake Alfred.

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