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POSTERS: Chemical and Biopesticide Control II

P-096 - Evaluating the ability of oxytetracycline to maintain efficacy after exposure to high temperatures

Tuesday, August 5, 2025
9:30 AM - 10:15 AM HST
Location: Exhibit Hall 3

    Presenting Author(s)

  • LM

    Lauren Fessler Mathews (she/her/hers)

    Graduate Research Assistant
    University of Florida
    Fort Myers, Florida, United States

    • Author(s)

  • AR

    Ana Redondo, n/a

    Research Coordinator
    Southwest Florida Research and Education Center, University of Florida
    Immokalee, Florida, United States

  • SK

    Sanju Kunwar, PhD (she/her/hers)

    Postdoctoral Researcher
    Southwest Florida Research and Education Center, University of Florida
    Quincy, Florida, United States

  • OB

    Ozgur Batuman, PhD

    Associate Professor
    Southwest Florida Research and Education Center, University of Florida
    Immokalee, Florida, United States

Abstract Text: Trunk injections of oxytetracycline (OTC) can help manage citrus greening or huanglongbing (HLB) disease presumptively caused by ‘Candidatus Liberibacter asiaticus’ (CLas). OTC is subject to degradation, the rate of which increases under intense heat and UV – conditions common to citrus groves. To evaluate if OTC can inhibit bacterial growth after prolonged exposure to high temperatures, both field and lab trials were conducted. Injectors were loaded with freshly prepared OTC then immediately injected into trees or left in the field exposed to environmental conditions for 6, 24, or 48 hours before injection. In the lab, inhibition of Xanthomonas citri subsp. citri was tested using aliquots from each timepoint. While direct comparison showed no significant difference in zone of inhibition (ZOI) size between fresh OTC and OTC exposed up to 72 hours, there was a weak negative correlation between ZOI size and exposure time. To assess HLB control in the field, visual disease ratings and CLas titers were taken monthly. Increase in canopy color was negatively correlated with exposure time but only freshly prepared OTC significantly decreased CLas titer compared to the water-injected control. Even 6 hours of exposure time rendered OTC ineffective for HLB control. It is theorized that adding ascorbic acid could slow the degradation rate of OTC and help maintain efficacy after exposure to heat. This is currently being investigated but preliminary results show potential. It is crucial to establish these guidelines for growers so that OTC trunk injections can effectively manage HLB.