By Ute Albrecht, Gabriel Pugina and Caroline Tardivo
Two years have passed since trunk injection of oxytetracycline (OTC) was approved for HLB management in Florida. Many growers have adopted this technology. While most reported positive responses, others did not.
The plant physiology team at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Southwest Florida Research and Education Center (SWFREC) has conducted numerous field trials. All of them found that OTC injections significantly increased fruit yield, fruit quality and juice quality. Naturally, results varied based on factors such as tree age, tree health status, scion and rootstock variety, trial location and the amount of OTC injected.
Unfortunately, positive responses were diminished by crop losses owing to several hurricanes, most recently Milton. While results may not meet expectations in terms of profitability even without losses from hurricanes, it remains clear that OTC injections are effective.
To truly determine how effective OTC injections or any other novel therapy are, it is imperative to use controls. Controls are trees that have not received the therapy (non-injected trees) and that can be compared against trees that have received it (OTC-injected trees). Only by comparing treated trees against non-treated (control) trees can an accurate assessment of the impact of a treatment be determined.
Comparing one year’s yield and pounds solid against the previous year’s, or comparing one location with another location, will not allow you to determine the true efficacy of a treatment. A case in point is a Hamlin trial where two consecutive years of injection were performed. The trial was in the main path of Hurricane Milton and experienced fruit loss of more than 50%. While fruit loss was extensive in both injected and non-injected trees, we still harvested up to 2.5-fold more fruit when trees had been injected. The trees were 18 years old at the time of the first injection.
The best results were observed when injections were administered on two (opposite) sides of the trunk (0.825 grams of OTC on each side). In fact, despite the fruit loss from Milton, trees that received this treatment had the same yield as in the previous year while the yield for the control trees was reduced by half. Fruit were also larger and had more soluble solids. If planning to move forward with OTC injections, or testing other novel treatments, it is therefore advised to leave a group of trees untreated in each location to serve as a control to truly assess treatment efficacy.
Ute Albrecht (ualbrecht@ufl.edu) is an associate professor; Gabriel Pugina and Caroline Tardivo are PhD students — all at the UF/IFAS SWFREC in Immokalee.
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