By Tripti Vashisth and Mary Sutton
Prolonged water deficits can negatively impact flowering, fruit growth, crop load and fruit quality. Unfortunately, HLB-affected trees are more susceptible to water deficits than healthy trees due to extensive root loss. Observing HLB-affected trees throughout the dry season showed that severely symptomatic trees consistently had lower leaf water potential than mildly symptomatic trees. This suggests HLB-affected trees experience more water deficits as the disease progresses. For this reason, adequate irrigation during the dry season is imperative in preventing drought stress.
This is particularly true for the sweet orange variety Valencia because flowering and fruit maturation periods overlap with the dry season. Researchers hypothesized that more frequent but smaller applications of water would better support the water needs of HLB-affected trees throughout the year. In an experiment, irrigation on control trees ran every other day for two hours (grower standard). Irrigation on the experimental trees ran three times every day for 20 minutes at a time. Both sets of trees received the same amount of water over time, but the experimental trees received water more often and in smaller amounts.
Trees receiving the frequent irrigation consistently had higher soil moisture content and mid-afternoon leaf water potential. This suggests the experimental trees were being maintained at a more well-watered state. The experimental trees also had significantly higher bud, fruitlet and leaf production during the spring flush. In fact, in 2023, the control trees saw a drought-stress-induced flowering event in late May that was not observed in the experimental trees. This all culminated in higher yields (more than double) at harvest over the two-year course of the study.
Tripti Vashisth is an associate professor, and Mary Sutton is a Ph.D. student — both at the University of Florida Institute of Food and Agricultural Sciences Citrus Research and Education Center in Lake Alfred.
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