Oxytetracycline Efficacy is Impacted by Exposure to Field Conditions
Posted August 2025
Researchers: Ozgur Batuman, Lauren Fessler Mathews, Sanju Kunwar, Ana Redondo
Contact: Ozgur Batuman, UF/IFAS SWFREC obatuman@ufl.edu
Summary:
Research conducted by scientists at the UF/IFAS has demonstrated that injections of oxytetracycline (OTC) can help to alleviate symptoms caused by huanglongbing (HLB) disease. OTC is a bacteriostatic compound that inhibits bacterial growth and replication. Like many antibiotics, OTC is sensitive to degradation under certain conditions, including high temperatures and intense UV radiation, which are inherent to Florida citrus groves. This degradation can be observed in the color change of the solution from bright yellow to dark brown. In July 2023, trees were injected with water, fresh OTC, and OTC that had been exposed to environmental conditions in the grove for 6, 24, or 48 hours. HLB management was evaluated monthly based on Candidatus Liberibacter asiaticus (CLas) titer quantification (i.e., qPCR) and visual disease ratings. Four months post-injection, only the freshly prepared OTC significantly reduced CLas titer compared to the water-injected control, indicating even 6 hours of exposure did not provide sufficient HLB control in this grove. This experiment was repeated in 2024 with the same treatments used in 2023, plus treatments with OTC that had been exposed for shorter intervals, including 1.5 and 3 hours. Data from 2024 is currently being analyzed. This study aims to establish a definitive threshold for the duration that filled injectors can be exposed to field conditions before losing efficacy in managing HLB.
Take Home Message:
- Field conditions, including high temperatures and intense UV radiation, degrade OTC.
- Always prepare fresh OTC and inject it into trees immediately; OTC degrades quickly.
- Well-irrigated trees can uptake the OTC faster, and may reduce the duration of OTC heat and UV exposure in the grove.
