ASHS 2025 Conference

Huanglongbing (HLB), associated with Candidatus Liberibacter asiaticus (CLas), continues to devastate citrus production worldwide. Individual protective covers (IPCs) offer a physical barrier against the Asian citrus psyllid, delaying CLas infection in young trees. However, once removed, trees become vulnerable to rapid infection. This study evaluates an integrated approach utilizing IPCs followed by systemic oxytetracycline (OTC) trunk injections to mitigate disease progression and sustain tree health. A field trial was established with ‘Valencia’ sweet orange (Citrus sinensis) grafted onto US-812 or US-942 rootstocks. Trees were either protected with IPCs for 18 months after planting (“late infected”) or had “open” IPCs (“early infected”). All trees received annual OTC injections in 2023 and 2024, beginning 10 months after IPC removal. CLas titers, OTC residues, tree growth, fruit yield and quality, leaf nutrient content, and root endorhizosphere microbial dynamics were assessed. Results indicate that IPCs successfully delayed infection, as late-infected trees maintained lower CLas titers for the first five months after IPC removal and exhibited denser canopies and larger scion and rootstock trunk diameters than early-infected trees. OTC injections significantly reduced CLas titers in leaves, with effects persisting for up to six months. However, no significant reductions in CLas titers were detected in fibrous roots, suggesting limited OTC translocation to the root system. Injected trees exhibited a greener canopy color, greater leaf size, higher chlorophyll content, higher yield, larger fruit size, and better juice quality compared to non-injected trees. No significant changes in leaf nutrient content were observed, and the root endorhizosphere microbial diversity remained unchanged across treatments, indicating minimal disruption to the microbial community due to the antibiotic. These findings provide evidence supporting the combination of IPCs and systemic delivery of OTC as an integrated strategy to manage HLB in new citrus plantings. IPCs delay the onset of infection, allowing trees to establish a healthy canopy and robust root system, while OTC injections aid in sustaining tree health post-infection. The integration of these practices provides a promising framework for establishing productive citrus orchards under HLB-endemic conditions.