By Ute Albrecht and Larissa Nunes
Citrus growers who injected oxytetracycline (OTC) last year most likely experienced sectoring, which is the appearance of some portions of the canopy looking considerably healthier than the rest of the tree.
RECENT RESEARCH
In a recent trial in a commercial citrus grove, University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) researchers injected nearly 200 Valencia/X-639 trees with 1.1 grams of OTC per tree (11,000 parts per million rate) using the FLexInject injectors. Injections were done into the rootstock trunk at the beginning of September 2023.
Two weeks after the injections, there was considerable yellowing and “bronzing” of the leaves on the side of the tree that had been injected. By the time of harvest (early April 2024), an obvious sectoring in terms of tree health was evident in all injected trees. The injected side looked considerably healthier with larger, greener leaves and more, better colored fruit than the non-injected side. Also, less fruit drop was noticed on the injected side.
Overall, a 2.25-fold (125%) yield increase was measured in response to the injections. For the juice-quality analysis, fruits were collected separately from the injected side and the opposite side of each tree. The average Brix was 11.2 on the injected side and 9.3 on the opposite side! In comparison, the Brix for the non-injected trees was only 8.5. The same was found for the Brix/acid ratio and the fruit rind color. Both were significantly better on the injected side than the opposite side. But even on the opposite side, findings were better compared to non-injected trees.
RECOMMENDATIONS
These results clearly document the sectoring that typically occurs when OTC injections are performed using current practices. The sectoring, and likely any leaf phytotoxic effects, may be moderated by splitting the injections into two on opposite sides of the trunk. However, this may be logistically challenging and/or cost prohibitive. It is therefore strongly recommended to perform the second-year injections on the side of the trunk opposite to first-year injections.
Sectoring may be especially evident in trees with a short trunk. The short trunk will prevent the OTC from dispersing evenly before reaching the canopy, thus causing sectoring. Injecting in line with the crotch of the scaffold branches may also reduce some of the sectoring.
Acknowledgments: Funding for this project was provided by the U.S. Department of Agriculture National Institute of Food and Agriculture and the Citrus Research and Development Foundation.
Ute Albrecht (ualbrecht@ufl.edu) is an associate professor, and Larissa Nunes is a PhD student, both at the UF/IFAS Southwest Florida Research and Education Center in Immokalee
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