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Why does fruit drop prematurely?

At UF/IFAS, we are working on finding solutions for Florida’s citrus growers. This is a summary of one project made possible by state legislative funding for the UF/IFAS Citrus Initiative during the 2018-19 cycle. It documents how we are making progress and  providing Florida growers with reasonable, pragmatic solutions to successfully grow citrus in the new age of citrus greening.

Researcher: Tripti Vashisth, Horticultural Sciences

IMPACT: Researchers found that fruit from severely HLB-symptomatic trees drop significantly more than mildly symptomatic trees. The fruit that drop are smaller sized than those that do not drop and are not deficient in carbohydrates. Thus, other factors that can influence the fruit size such as water uptake and hormonal balance should be studied in future research projects.

Commercial citrus trees routinely lose some of their developing fruit before harvest. This phenomenon, known as fruit drop, happens at three growth stages: during spring flowering, a month or two after flowering, and during the last few weeks before harvest. The matured fruit simply drop to the ground and cannot be marketed, so they are considered waste. Observations indicate that Florida groves affected by citrus greening disease, also known as Huanglongbing or HLB, often drop an unusually high percentage of their fruit just before harvest — up to 40% in some cases.

Because scientists are uncertain how HLB may promote premature fruit drop, UF/IFAS Citrus Research and Education Center horticulturalist Tripti Vashisth led a study to investigate the disease’s effect on fruit drop. First, the trees were classified into three groups, based upon the severity of visible disease symptoms. Further observations showed the severely affected trees had lower yields, produced smaller fruit, and dropped a greater percentage of developing fruit compared with less-affected trees. Also, the fruit remaining on severely affected trees were more likely to be loosely attached.

Though the researchers did not pinpoint the cause of premature fruit drop, previous experiments have indicated it cannot be remedied with pruning, thinning or application of plant hormones. This was the first citrus study to report that there is a relationship between fruit size and fruit drop.

To read about more research projects funded through the Citrus Initiative visit  or the  website