Reducing Fruit Drop in HLB Citrus

By Tripti Vashisth

Fruit drop has become one of the biggest challenges for Florida citrus growers, especially in groves hit hard by HLB. On top of the disease, recent hurricanes like Ian and Milton have made the problem worse, causing fruit to drop not just during the storm but often weeks later. Other stresses — such as drought, flooding or cold snaps — can also speed up fruit loss and tree decline.

Plant growth regulators (PGRs) can be used as tools to help growers keep more fruit on trees. Two products in particular are showing results: gibberellic acid (GA, ProGibb LV Plus by Valent BioSciences) and 2,4-D (Citrus Fix by AMVAC). GA helps keep the peel and canopy healthier for longer. 2,4-D works directly to slow the fruit’s natural “drop signal.” Both also push back against ethylene, the plant hormone that drives premature drop in HLB trees.

A two-year field trial on mature Valencia in Polk County tested different approaches:

• An untreated control
• A single November spray of 2,4-D at the label rate
• Three smaller sprays at 1 ounce per acre spread out September through November
• A tank mix of 2,4-D (3.2 ounces per acre) plus GA (10 ounces per acre)

The results were clear. The GA + 2,4-D combination cut fruit drop by about 16% in the first year. In the second year — despite Hurricane Milton — trees treated with either 2,4-D alone or the GA + 2,4-D mix lost at least 20% less fruit than untreated trees. Treated trees also produced more fruit per canopy size, showing better efficiency even under storm stress. Multiple small sprays of 2,4-D did not provide any extra benefit in reducing fruit drop.

The takeaway message for growers is that one well-timed November spray of 2,4-D along GA works very well in reducing fruit drop. Using these PGRs, especially after hurricanes, can help reduce drop and protect yields in HLB-affected citrus.

Tripti Vashisth is associate center director and associate professor at the University of Florida Institute of Food and Agricultural Sciences Citrus Research and Education Center in Lake Alfred.