Many Florida citrus growers were among the approximately 300 people who registered for a Sept. 21 virtual seminar telling how gibberellic acid (GA) can improve Valencia orange yields. Valencias, at 30.1 million boxes, made up slightly more than half of Florida’s total citrus crop in the 2020-21 season.
Presenter Tripti Vashisth started her presentation by saying that GA, already available for use in citrus, is another tool for coping with HLB. She said properly applied GA applications can improve fruit set, development and yield. Vashisth is a University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) horticulturist at the Citrus Research and Education Center (CREC) in Lake Alfred.
After summarizing five years of research on GA, Vashisth said Valencia growers can begin using the plant growth regulator now to improve their yields. She recommended growers apply GA monthly from September to early January.
See the UF/IFAS presentation for specifics, including GA application rates and economic benefits.
In Vashisth’s 2016-21 study of Valencias on Swingle rootstock, GA increased fruit yields substantially compared to untreated plots when applied monthly from September to January. The highest pound-per-tree fruit yield occurred in the 2018-19 season when the GA treatment yielded 282 pounds versus 209 pounds for an untreated plot.
There are some precautions growers should be aware of when using GA. Vashisth said GA slows down the color change process or can even reverse the color change. For that reason, fresh fruit growers should take extra precautions when using GA. Vashisth said fresh fruit may require a 4- to 5-month gap between the last GA application and harvest. Traditionally, only about 5% of Florida oranges go to the fresh market; the vast majority is processed into juice.
GA also suppresses flowering, Vashisth cautioned. Applying the product too close to bloom could negatively affect bloom and fruit drop. Do not apply GA after January 10, and possibly not after Dec. 31, she said.
Recent UF/IFAS research showed that many HLB symptoms on trees are the result of oxidative stress caused by the disease. In an introduction to Vashisth’s presentation, CREC Director Michael Rogers noted that studies indicated GA reduces oxidative stress and improves tree health and yield.
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