Managing endemic huanglongbing in commercial citrus production through vascular delivery of oxytetracycline

The bacterial disease huanglongbing (HLB) is devastating citrus industries around the world. Recent studies have identified trunk injection of oxytetracycline (OTC) as an effective method to reduce pathogen titers and restore citrus tree health and productivity. Here we assess the efficacy of OTC injections to mitigate HLB in a commercial citrus orchard in Florida over two production cycles. Nine-year-old ‘Valencia’ orange (Citrus sinensis) trees were injected with two rates of OTC in May 2022 and 2023 using two different injection methods and compared against non-injected trees. Regardless of the method, OTC injection significantly improved fruit yield and juice quality. At the lower rate (0.55 g OTC/tree) fruit yield increased by up to 66 % in year 1 and 95 % in year 2. At the higher rate (1.1 g OTC/tree) fruit yield increased by up to 70 % in year 1 and 121 % in year 2. Significant increases were also measured for fruit size, fruit weight, juice color, and soluble solids, regardless of the OTC rate although the higher rate generally produced better results. OTC residues in the fruits collected at harvest were below the maximum allowed level, regardless of the rate. Leaf bacterial titers measured one year after each injection were not different between injected and non-injected trees, suggesting that reinfection occurred and that repeated injections are necessary to maintain the beneficial effects of this therapy. The economic analysis showed that the cumulative result of OTC treatments over two seasons is positive, denoting that their benefit outweighed their cost.