Systemic Delivery of Oxytetracycline by Drill-Based and Drill-Free Trunk Injection for Treatment of Huanglongbing in Young Sweet Orange Trees

The systemic delivery of oxytetracycline (OTC) by trunk injection has emerged as a viable strategy to manage huanglongbing (HLB, also known as citrus greening), a bacterial disease devastating citrus production around the world. This study examines the efficacy of delivering OTC systemically into the trunk of young, HLB-affected citrus trees using a drill-based or a drill-free system to improve tree health and productivity. Two field trials were conducted in two commercial production sites in Florida. Trees were four years old at the start of the study and composed of ‘Valencia’ or ‘OLL-8’ sweet orange (Citrus sinensis) scion grafted on X-639 (C. reticulata × Poncirus trifoliata) rootstock. Injections were performed in spring or late summer/early fall in 2022 and 2023. Using the drill-based system, 0.79 g of OTC was administered into each tree, whereas 0.15 g or 0.3 g was administered using the drill-free system. Delivering a higher dose of OTC by drill-based injection increased fruit yield and improved juice quality more than delivering lower doses by drill-free injection, though responses varied between cultivars. Injections in late summer/early fall increased the juice total soluble solids content considerably more than injections in spring. However, fall injections resulted in OTC fruit residues exceeding the maximum allowed level. Trunk injury was more extensive when OTC was applied with the drill-free system than when it was applied with the drill-based system.