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Bactericide Applications for HLB Control

At UF/IFAS, we are working on finding solutions for Florida’s citrus growers. This is a summary of one project made possible by state legislative funding for the UF/IFAS Citrus Initiative during the 2018-19 cycle. It documents how we are making progress and  providing Florida growers with reasonable, pragmatic solutions to successfully grow citrus in the new age of citrus greening.

Researcher: Nian Wang, Microbiology and Cell Science

IMPACT: Findings suggest that bactericide applications as legally allowed at present may have no significant benefit to greening-affected trees.

In 2017, the U.S. Environmental Protection Agency granted an emergency exemption to Florida citrus growers, allowing them to test bactericide applications. The exemption permitted growers to spray their trees with solutions containing the bactericides oxytetracycline and streptomycin to fight
citrus greening.

Recent studies led by UF/IFAS Citrus Research and Education Center microbiologist Nian Wang indicated these compounds had no significant benefit to trees when applied in spray form because very little bactericide made its way into the leaf where the pathogen resides.

However, a companion study suggests that bactericides provide excellent control of greening disease when injected into the trunks of affected trees.

Wang and his associates conducted field trials using three bactericides and eight environmentally friendly compounds believed to activate or fortify natural defense systems in plants. The results showed that any of the bactericides — oxytetracycline, streptomycin, and penicillin — when injected into the tree could provide excellent control of HLB, by reducing bacterial concentrations and halting disease progress. Four of the environmentally friendly compounds provided significant disease control, though generally they did not perform as impressively as the bactericides.

At present, federal regulations do not allow U.S. citrus growers to apply bactericides to citrus trees via trunk injection, but Wang plans to continue researching this application method to explore its potential benefits and drawbacks that can be used to help facilitate the registration of these bactericides using trunk applications.

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