Oxytetracycline Injections - Sectoring and Phytotoxicity
Posted August 2025
Researchers: Ute Albrecht, Larissa Nunes, Gabriel Pugina, Igor Rodrigues
Contact: Ute Albrecht, UF/IFAS SWFREC ualbrecht@ufl.edu
Summary:
Trunk injections are mostly performed on one side of the tree. In the following year, the injected side generally looks considerably better than the non-injected side. This is also reflected in the better quality of the fruits in terms of size, peel color, and °Brix. To reduce sectoring, injections may be performed two-sided, that is injecting half the dose of oxytetracycline (OTC) on two (opposite) sides of the trunk. However, even with two-sided injections, some sectoring may still occur. Dye injections can visualize this phenomenon. The photo shows that despite the two-sided injection, most of the dye moved into one branch of the tree, likely the one originating closest to the injection side and most metabolically active at the time of injection. Such dye studies also demonstrate why phytotoxic effects can occur in response to OTC injections. Those sections in the canopy receiving most of the chemical are likely to express the most phytotoxicity. Moderate phytotoxicity manifests as yellowing of the leaves, which usually disappears during the growing season. These sections of the canopy will ultimately be the healthiest. Severe phytotoxicity includes twig die-back and fruit drop but is usually limited to small sectors in the canopy. Phytotoxic effects do not seem to be related to the month of injection but rather to local growing conditions. Apart from performing two-sided injections, reducing tree stress prior to the injections may help reduce the risk of phytotoxicity. Some sectoring will always occur but will likely be less evident after consecutive years of injection.
Take Home Message:
- Uneven OTC distribution may lead to phytotoxicity and sectoring.
- Both phytotoxicity and sectoring may be reduced by two-sided injection.
- Dye injections visualize the uneven distribution in the canopy.
