Researchers with UF/IFAS tested whether adjuvants would help improve the intake of the bactericide oxytetracycline in citrus trees.

The use of bactericides was approved in 2016 to combat citrus greening, but citrus growers have not seen the benefits in fighting citrus greening suggested by research. During a Citrus Expo presentation,  UF/IFAS assistant professor of horticultural sciences, Christopher Vincent, shared the results of research into using adjuvants to improve the delivery of foliar-applied oxytetracycline, a bactericide, according to a Citrus Industry article. See the details below.

Adjuvants do Not Improve Oxytetracycline

The study used six-year-old Hamlin trees on Swingle rootstock that were infected with citrus greening and had never been treated with antimicrobial applications. Researchers used a CO2 backpack sprayer to apply oxytetracycline and an adjuvant for foliar applications. Additionally, researchers also looked at the results of injecting the bactericide with tree-injection syringes.

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

Unfortunately, no adjuvant was successful. “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,” Vincent said, according to the article.

However, the study did find that oxytetracycline delivered by injection did reduce the bacterium that causes citrus greening.

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