Ute Albrecht, a scientist with the University of Florida Institute of Food and Agricultural Sciences, recently released findings from trials conducted regarding the injection of antibiotics into the trunks of citrus trees. The goal is to provide protection for the trees against HLB while simultaneously reducing the undesired effects of traditional forms of antibiotic application, including the risks to non-target organisms and workers.
Trunk injection, or endotherapy, is accomplished by delivering the antibiotics directly into trees through the xylem. This allows the material to then be distributed efficiently throughout the plant via the transpiration system and into the phloem, where the Candidatus Liberibacter asiaticus (CLas) bacteria that causes HLB resides. This method is successfully utilized to combat various pathogens in a number of species, including the fungal infection that causes laurel wilt in Florida avocados.
One of the main benefits of trunk injection as a delivery method for antibiotics is that the residual effects last significantly longer than they do with other forms of delivery. Other benefits include synchronization of flushing and flowering, improved quality of fruit internally and externally, decreased fruit drop, and increased yield. This was the result of injection specifically with the antibiotic oxytetracycline. These benefits were maintained through the second year of study without additional injection, despite an increase in the concentration of CLas bacteria present.
Albrecht also investigated the effectiveness of injecting citrus trees with the pesticide imidacloprid to control the Asian citrus psyllids that spread the CLas bacteria. While this insecticide increased psyllid mortality for two weeks after the injection, it was no longer effective two months later.
There are a number of factors that influence how quickly the injected material is distributed through the tree by the transpiration system, such as weather, season, and time of day when the injection is made. Whether the injection is made into the rootstock or scion also impacts uptake and distribution. Spring injection resulted in larger fruits. Injury to the tree from the injection seems to be best treated with no treatment at all, although more research needs to be conducted to determine long-term effects.
This column is sponsored by Griffin Fertilizer Co., and the opinions expressed herein may not reflect those of CFAN or of its advertisers.
BIO: Mike Roberts is the Vice President of the Frostproof, Fla.-based Griffin Fertilizer Co. Roberts joined the company in November 2011. He has spent the majority of his career in the fertilizer/agchem industry. Roberts earned a Bachelor of Science degree in citrus production from Florida Southern College in Lakeland. For more information, visit griffinfertilizer.com.