Trunk Injection for HLB: Pros and Con

The pros of injecting the antibiotic oxytetracycline (OTC) into citrus tree trunks to combat HLB appear to be numerous, including increased fruit yield, according to scientist Ute Albrecht. On the other hand, the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) researcher only discussed one con, but it was a big one.

“Trunk injections cause injury, and long-term effects need to be evaluated,” she reported in a well-attended (more than 250 participants) virtual seminar on July 22.

In Albrecht’s trials, injections of OTC were made into Valencia orange tree trunks in October 2020 and April 2021. Controls included injection of water and no injection at all.

A slide in her presentation stated: “Injected OTC appears to move to the phloem, reduces CLas titers, and improves tree health, fruit quality and yield.” CLas titer is a measure of the bacterium Candidatus Liberibacter asiaticus in a tree; CLas is the HLB causal agent.

According to Albrecht, the OTC injections reduced fruit drop and increased yield significantly. The injections also improved internal and external fruit quality significantly. The effect of fruit production remained in year two without any additional injection, although CLas titers increased. This indicates that injections may not need to be performed annually.

Other findings included:

• Citrus fruit were larger following the spring OTC injection than after the fall injection.
• OTC residue in fruit decreases dramatically within 30 to 60 days after injection.
• OTC synchronizes flushing and flowering.

On the same dates researchers injected the OTC for HLB control, they injected the insecticide imidacloprid into trunks to test its control of HLB-spreading Asian citrus psyllids. Albrecht reported that the imidacloprid did not show long-term efficacy. Imidacloprid significantly increased psyllid mortality two weeks after injection but not after two months.

UF/IFAS head Scott Angle addressed the virtual seminar audience immediately prior to Albrecht’s presentation. He said some UF/IFAS presentations like Albrecht’s are being made to growers and others more quickly than they used to be. He said UF/IFAS wants to “share the information we have and let you make up your own mind” how or whether to use it. “We know we don’t have years and years” to develop solutions to HLB, he said. 

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