Citrus huanglongbing (HLB) is one of the most destructive diseases of citrus worldwide,and is threatening the survival of the Floridian citrus industry.Currently,there is no established cure for this century-old and emerging disease.As a possible control strategy for citrus HLB,therapeutic compounds were screened using a propagation test system with Las-infected periwinkle and citrus plants.The results demonstrated that the combination of penicillin and streptomycin (PS) was effective in eliminating or suppressing the Las bacterium and provided a therapeutically effective level of control for a much longer period of time than when administering either antibiotic separately.When treated with the PS,Las-infected periwinkle cuttings achieved 70% of regeneration rates vs.less than 50% with other treatments.The Las bacterial titers in the infected periwinkle plants,as measured by quantitative real-time PCR,decreased significantly following root-soaking or foliar-spraying with PS.Application of the PS via trunk injection or root soaking also eliminated or suppressed the Las bacterium in the HLB-affected citrus plants.This may provide a useful tool for the management of citrus HLB and other Liberibacter-associated diseases.