By Ute Albrecht
Replicated field studies have demonstrated positive effects of oxytetracycline administered by trunk injection to manage HLB. In October 2022, a 24(c) special local need label was approved that allows the use of this technology in Florida, and final clearance was given in January.
When practicing trunk injection, it is important to do so properly and to be aware that the injection itself causes injury, which is exacerbated by oxytetracycline. Moreover, trunk injection does not replace other essential tree care such as vector control and nutrition. When using this technology on a large scale, the following best practices are recommended to ensure the highest efficacy and the least harm to the tree:
- Follow label directions.
- Inject after the main flowering period to prevent exposure of pollinators.
- Uptake and distribution of injected materials is driven by transpiration. Transpiration is the process of evaporation of water vapor on the leaf surface through the stomata. The loss of water vapor pulls water (and therefore injected materials) from the stem and roots upwards. Therefore: A) Inject when leaves are fully expanded (not during flush) to ensure efficient uptake and distribution. B) As much as possible, inject during mid- to late morning when trees are actively transpiring. Injections in the afternoon are likely to be less effective and may also increase the risk for phytotoxicity.
- Avoid injecting during the hottest time of the day and season. There have been reports of phytotoxicity (leaf bronzing) when injections were conducted in August.
- Use a sharp brad-point drill bit to minimize injury.
- Drill the hole no deeper than necessary. The inner (older) wood of the trunk is metabolically less active, and drilling results in more internal damage and dysfunction.
- Do not use any wound sealants or plugs/stoppers to seal the injection hole. These inhibit the tree’s ability to effectively compartmentalize (heal) the wound.
- Remember that trees can become reinfected. Oxytetracycline injection is not a replacement for psyllid control.
- Although the label allows it, it is not advised to inject trees with a trunk diameter of less than 2.5 inches.
- Inject trees only once annually and leave a preharvest interval of at least 180 days.
Trunk injection of oxytetracycline can provide much needed help for growers, provided it is done properly, and other tree care is not neglected. Please pursue this new technology with care as researchers develop more information on best practices.
Ute Albrecht is an associate professor at the University of Florida Institute of Food and Agricultural Sciences Southwest Florida Research and Education Center in Immokalee.
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