Oxytetracycline Bactericide Sprays Being Used on Citrus Trees Not Effective, New Study Says

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Due to an epidemic of citrus greening disease, which is caused by a bacteria that is carried by an invasive flying insect known as the Asia citrus psyllid (Nordlie, 2019). Also known as huanglongbing, or HLB, the disease is eventually fatal but, with supportive management the trees can still produce for several years.

So, bactericides are used to treat infected tress. Citrus growers in Florida have had special permission from the EPA since 2016 to spray citrus groves with bactericide solutions containing oxytetracycline or streptomycin, despite concerns about how widespread use of antibiotics and other bactericides is increasing antibiotic resistance.

But, new research out of the University Florida’s Institute of Food and Agricultural Sciences (UF/IFAS) suggests that the spraying method used over the last three years is largely ineffective.

The problem, reports UF/IFAS’ Citrus Research and Education Center researchers in this press release, is getting the bactericide into the infected plant tissue.  “Our researchers did not have much success on that front using foliar sprays, and saw no significant effects from the treatments.”  They suspect the waxy coating on citrus leaves may be preventing foliar penetration.

In contrast, the bactericides were mostly effective when injected directly into the trunks of the trees.

This story is an example of how pesticide regulation can often be out of step with science, leading to unnecessary applications of ineffective pesticides.

Sources:

Li, Jinyun, Pang, Zhiqian, Duan, Shuo, Lee, Donghwan, Kolbasov, Vladimir, & Wang, Nian; “The in planta effective concentration of oxytetracycline against Candidatus Liberibacter asiaticus for suppression of citrus Huanglongbing;” Phytopathology, 2019; DOI: 10.1094/PHYTO-06-19-0198-R.

Tom Nordlie; “UF/IFAS Study: Oxytetracycline Sprays May Not Protect Citrus Trees From Greening Disease Effectively, Though Trunk Injections Show Promise;” Press Release, Univeristy of Florida Institute of Food and Agricultural Sciences, Date published: 8/2/2019, Date accessed: 8/7/2019.