Adjuvants Did Not Improve Delivery of Foliar-Applied Oxytetracycline

Tacy CalliesCitrus Expo


In 2016, federal authorities began allowing Florida citrus growers to spray oxytetracycline solutions on their trees to combat citrus greening disease. Since then, researchers have been investigating oxytetracycline delivery methods.

In a Citrus Expo presentation, Christopher Vincent, assistant professor of horticultural sciences at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Citrus Research and Education Center, shared results from a UF/IFAS study. The goal of the study was to determine if adjuvants can improve the delivery of foliar-applied oxytetracycline.

“Our objective was to assess the role of adjuvants in delivery of oxytetracycline through applications,” Vincent said. “And of course, we wanted to know which adjuvants are most effective in achieving delivery.”

For this study, researchers used six-year-old Hamlin trees on Swingle rootstock. All trees were HLB-affected and had never received antimicrobial applications before. Researchers used tree-injection syringes and a CO2 backpack sprayer for foliar applications.

According to Vincent, researchers wanted to evaluate how much oxytetracycline was in the leaves as well as how much had moved around the plant. To assess the systemic delivery, researchers bagged one shoot on every tree to keep the shoot protected from the application. Any oxytetracycline that was found in the leaves coming from that shoot would have been found from oxytetracycline moving through the plant due to the application through the spray.

Based on the findings from the study, Vincent reported that no foliar adjuvant increased the delivery of antibiotic. “Of the oxytetracycline that makes it into the leaf, only about 20 percent of that is being actually cycled around systemically in the plant. The concentrations that were systemically delivered were about 5 to 12 percent of those delivered by injection,” he said.

Another finding from the study was that only oxytetracycline delivered by injection reduced the bacterium that causes citrus greening.

View Vincent’s full Citrus Expo presentation here. All Citrus Expo presentations and the continuing education units that can be earned by watching them will remain available through the end of 2020.

This article was written by Ashley Robinson, AgNet Media communications intern in Gainesville, Florida.