Trunk injection of commercial oxytetracycline for HLB management in young Grapefruit trees using a novel injection system

Authors: LOCATELLI, GUILHERME - University Of Florida; THOMPSON, LUKE - Cornell University; Shatters, Robert - Bob; Heck, Michelle; ROSSI, LORENZO - University Of Florida

Submitted to: International Research Conference on Huanglongbing
Publication Type: Abstract Only
Publication Acceptance Date: 3/1/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Huanglongbing (HLB) is considered one of the most devastating diseases to the global citrus industry. It has drastically reduced the yields in Florida, especially for grapefruits whereas the forecast for the 2022-2023 season is expected to be the lowest production since the 1911-1912 season. The disease is associated with the bacteria ‘Candidatus Liberibacter asiaticus’ and vectored by the Asian citrus psyllid (Diaphorina citri). The pathogen resides in the phloem of infected trees making control of the disease difficult. Recently, in Florida, trunk injections of oxytetracycline (OTC) have been approved for the treatment of HLB-affected citrus trees. In this study, 3-year-old ‘Ruby Red’ grapefruit trees grafted on UFR-17 were injected with either of two different OTC formulations or with distilled water (control) once or twice during the 2023 season. The first injections occurred in February 2023 and the second injections occurred in June 2023 using a novel delivery system that does not require drilling and targets the outer ring of vascular tissue under the bark. Trees injected once received 75 mg of the active ingredient (OTC-HCL), and trees injected twice received 150 mg of the active ingredient. Tree uptake of OTC formulations was measured 2 and 7 days after each injection and leaves were collected to measure OTC residues 7, 14 and 30 days after each injection. Trees were monitored at the time of initial injections and monthly for disease index (DI) and canopy volume. The rootstock injection site of each tree was monitored for external damage. Preharvest fruit drop, yield, and fruit quality will be measured prior to or at the harvest. Tree uptake 7 days after injection of each OTC formulation was greater than 90% for all treatments in the first injection and was 100% for all treatments in the second injection. Visual improvement in tree health was observed in trees that received an OTC treatment independent of the OTC formulation that was used at 2, 3 and 4 months after injection. The rootstock injection site showed more external damage in trees treated with OTC compared to control.