Trunk-Injection Takeaways Presented

Researcher Ute Albrecht on April 21 shared lessons learned from three years of oxytetracycline (OTC) trunk injection for HLB management in Florida. Albrecht is an associate professor with the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) specializing in citrus plant physiology. She works at the Southwest Florida Research and Education Center.

Albrecht reported on results of a Valencia orange-on-Swingle rootstock field trial planted in Polk County in 2005 and trunk-injected with OTC from 2023 to 2026:

• The month when the injection was made had little influence on yield, although April injections reduced the yield slightly compared to July injection.
• Late injections increased the Brix more than early injections.
• Late injections increased pound solids more than early injections.
• Late injections decreased acidity slightly more than early injections.

Regarding a trial to determine the impacts of an off-year (not injecting OTC in year 2), Albrecht reported that:

• Yield is reduced in the off-year but is still higher compared to the control.
• An off-year reduces the pound solids to nearly the same level as the control.
• Off-year yield reductions carry over slightly into year 3.
• Off-year juice quality reductions do not carry over into year 3.

A Valencia trial on various rootstocks was planted in 2015 in Polk County at 303 trees per acre. The rootstocks were US-812, US-942, US-897, UFR-2, UFR-4 and Carrizo. OTC injections were made in 2023, 2024 and 2025. The OTC-treated trees yielded 462 boxes per acre. Control trees yielded 219 boxes per acre.

Albrecht also offered the following observations and suggestions:

• OTC uptake seems to be a little faster when injecting into the scion than into the rootstock.
• Bark cracking/trunk injury is less severe when injecting into the rootstock than into the scion.
• It is better to inject young trees into the rootstock.
• Use a smaller applicator to reduce trunk injury.

UF/IFAS multi-county citrus Extension agent Mongi Zekri hosted Albrecht’s virtual presentation, which attracted more than 40 participants.