Frequent Irrigation Increases Yield in Huanglongbing-Affected Sweet Orange

A steady decline in sweet orange ( Citrus sinensis ) tree health is associated with Huanglongbing (HLB). Part of this decline includes root dieback, which limits their capacity to take up water. For this reason, affected trees tend to be more susceptible to drought stress. This raises a significant concern during the dry season (October to May) when trees are largely dependent on supplemental irrigation for water. Unfortunately, most growers continue using irrigation schedules that were optimized for healthy trees. We hypothesized that irrigating more frequently but in smaller amounts would provide more opportunities for uptake and improve water relations in HLB-affected sweet orange trees. The control treatment received the standard practice of irrigating every other day for 2 h (12 gal/h). The experimental treatment received water every day, three times a day, for 20 min (12 gal/h). The two treatments received the same amount of water over the course of a week, but the experimental treatment received water more often. Treatments were initiated before flowering in Jan 2022 and were continued for 2 consecutive years. Upon implementation, tree water status improved in the experimental trees as reflected in higher midday leaf water potentials than in the control. In the second year, flowering was more synchronized in the experimental treatment. The control treatment saw two peaks in bud production with the latter one being consistent with a drought stress–induced flowering event. The experimental trees also saw increases in fruit set in year 1 (41% higher in experimental) and year 2 (18% higher in experimental). Trees receiving the experimental and control treatments dropped a similar proportion of their crop load during June drop and preharvest fruit drop in years 1 and 2. Finally, the experimental treatment resulted in significantly higher yields on average than the control in both year 1 and year 2. Altogether, more frequent irrigation improved sweet orange tree productivity by maintaining a better water status.