By Tripti Vashisth
Huanglongbing (HLB) severity is associated with small fruit sizes and lower fruit numbers at harvest. Moreover, small fruit are more likely to drop and drop earlier during preharvest fruit drop. Unfortunately, management practices suggested to increase fruit size or reduce drop have had mixed results.
So, before looking for ways to increase fruit size and number, it is necessary to first identify when and why differences in size and retention occur. To do this, University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) researchers followed fruit on mildly and severely HLB-symptomatic trees from bud to harvest.
Mild trees had a higher rate of flowering and fruit set, which suggests HLB affects fruit number early on. Mild trees have a denser canopy with more fruiting wood and better source-to-sink ratio available for flower and fruit production. Maintaining canopy density should be a priority in maintaining fruit numbers. While HLB-affected trees are more susceptible to drought stress, mild trees experience less water deficits. This may contribute to their improved flowering and fruit set as these processes correspond with the Florida dry season.
UF/IFAS researchers are currently investigating irrigation practices to further mitigate this susceptibility. An experimental treatment involved irrigating three times daily for twenty minutes each while the control involved irrigating every other day for two hours. The experimental schedule increased bud production and fruit set while improving yield at harvest. Trees under the control regime experienced a late burst of flowering consistent with drought stress. This was not seen in the experimental schedule, which suggests that frequent, smaller doses of irrigation maintain trees in a well-watered state.
- Canopy density largely limits flowering, fruit set and final fruit numbers.
- Mildly affected HLB trees experience less water deficits than severely affected trees.
- Frequent, small doses of irrigation increase bud production and fruit set leading to improved yield.
Acknowledgment: This is a UF/IFAS Citrus Initiative project funded by the Florida State legislature.
Tripti Vashisth is an associate professor at the UF/IFAS Citrus Research and Education Center in Lake Alfred.