Combine Plant Growth Regulators for Most Benefit

Josh McGillCitrus Expo, PGRs

Using the plant growth regulators (PGRs) gibberellic acid (GA), 2,4-D and cytokinin in combination can maximize the benefit for HLB-affected trees, researcher Tripti Vashisth reported recently. The University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) associate professor of citrus horticulture and production works at the Citrus Research and Education Center in Lake Alfred. She discussed the benefits of PGRs at August’s Citrus & Specialty Crop Expo.


Vashisth emphasized that timely PGR application is critical. She recommended applying cytokinin in spring, GA in summer and 2,4-D in fall. She noted that the combination of cytokinin in spring and GA in summer increased yield by about 90 pounds per tree.

Zeroing in on GA timing, Vashisth recommended the product be applied to Hamlin oranges from August to November and to Valencia oranges from September to December. She said GA use should be avoided from January to May, reporting that March to May applications enhance fruit set, which is not desirable given current tree conditions.

Vashisth said GA applications on grapefruit trees can help improve canopy, but GA should not be sprayed on grapefruit or any fresh variety past September.

Vashisth said GA can improve yield and canopy. 2,4-D can reduce the pre-harvest drop of fruit but doesn’t seem to be helpful when fruit drop isn’t an issue. Cytokinin can improve canopy growth.

In recent years, Vashisth has led UF/IFAS research on how PGRs can improve the health of HLB-infected trees. She has conducted extensive research on the use of GA. Learn more about her GA work here. Also, read about her research on cytokinin

See Vashisth’s full Expo presentation, Use of PGRs to Improve the Growth and Productivity of HLB-affected Trees.

Additional presentations from the Citrus & Specialty Crop Expo can be viewed here.

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Ernie Neff

Senior Correspondent at Large

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