Is There a Solution for Citrus Fruit Drop?
May 29, 2020 
Staying on top of citrus fruit drop is critical for growers to have a successful harvest. Photo by Frank Giles
Plain and simple: Fruit left unharvested is a waste for growers and consumers alike. The citrus industry certainly cannot afford to leave anything on the ground. That is why UF/IFAS citrus scientists Tripti Vashisth and Fernando Alferez are trying to reduce the amount of fruit that drops from Hamlin and Valencia trees prior to harvest.
According to Alferez, about 10% to 15% of citrus fruit drops from a healthy tree on a normal basis. The pressure of citrus greening (HLB) ups the chance for drop though. In the 2012-2013 season, researchers and citrus growers reported about 25% of crop loss because of greening-associated fruit drop. Now, depending on the citrus variety, growers may see a pre-harvest drop up to 50%.
So, what can be done? The two scientists are looking into the effect of removing fruitlets (fruit that’s less than 2 centimeters in diameter) from so-called “off-blooms.”
Preliminary experiments show that removing fruitlets from off-blooms when Hamlin oranges are mature results in more mature fruit hanging onto citrus trees – as opposed to dropping — Alferez confirmed. This might increase yield because the mature fruit drops less.
Valencia oranges are more complex, as several blooms occur during the last part of fruit maturation, Alferez pointed out.
Another preliminary finding is that insufficient carbohydrates do not cause fruit drop. Therefore, the researchers recommend growers use good irrigation and nutrition practices during the fruit-development period. Vashisth and Alferez also say if growers apply gibberellic acid during the fruit-development period, it can help reduce fruit drop.
“Our preliminary findings are important because they show that the fruit drop related to HLB is not a simple process,” Vashisth said. “There is no single cause for the fruit to drop. There have to be more causes, and that is what we are trying to understand now.”
In healthy trees, competition for resources between mature and fruitlets causes some ready-to-harvest fruit to drop. Trees with HLB have their own set of issues.
“In Hamlin and Valencia oranges, we have observed several off-blooms resulting in new fruit as the current crop is already developing,” Vashisth said. “This is normal in healthy trees growing in tropical or subtropical regions, such as Florida. However, in an HLB-affected tree, this may compromise the tree’s ability to keep fruit. It may also reduce yield, because the new fruitlets and mature citrus compete for carbohydrates.”
Resources for this research is made possible by state legislative funding for the UF/IFAS Citrus Initiative and UF/IFAS new faculty.
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