Wound reaction to trunk injection of oxytetracycline or water in huanglongbing-affected sweet orange (Citrus sinensis) trees

Key message

Trunk injection causes injury to trees and best practices must be established for use of this technology to manage vascular diseases such as huanglongbing.

Abstract

Trunk injection is a technique for applying plant protection compounds that has demonstrated efficacy for management of huanglongbing (HLB), a bacterial disease which has devastated the Florida citrus industry. Recently, the antibacterial oxytetracycline has been approved for trunk injection in citrus in Florida. Despite its potential for restoring health of HLB-affected trees, little information is available on the trees’ ability to heal and compartmentalize the wounds caused by trunk injection and the interaction with season and other factors. In this study, 5-year-old HLB-affected sweet orange (Citrus sinensis) trees were injected bi-monthly to measure seasonal differences in the rate of uptake of injected water and to compare the external and internal wound reaction in both scion and rootstock. Also investigated was the wound reaction after trunk injection of an injectable formulation of oxytetracycline. Injection during spring and summer promoted more rapid wound closure compared to injection in fall or winter, and injection into the scion was less damaging than injection into the rootstock. Although citrus trees effectively compartmentalized wounds inflicted by injection of water, injection of oxytetracycline impeded wound healing and increased internal damage. Application of a fungicide or pruning sealant increased the size of the wound internally and externally. For trunk injection to be adopted for use in commercial citrus orchards, the benefits of injection must outweigh the risks of wounding associated with the application method. This study provides first insight on some of the best practices for effectively utilizing trunk injection in citrus as a crop protection strategy.