The purpose of this project is to reveal the mechanisms of bactericide uptake and transport in citrus plant and establish a theoretical basis for developing technologies to improve the efficacy of bactericides (oxytetracycline and streptomycin), which is helpful to provide potential solution to the development of effective chemotherapeutic tools for HLB management. Achieving this outcome will require progress in the following three tasks: (1) to compare the delivery efficacy of bactericides with three application methods (foliar spraying, truck injection, and root administration) based on the uptake and dynamic movement/distribution of the bactericides within the tree; (2) to clarify the systemic movement and transportation mechanisms of bactericides within the phloem of tree; and (3) to investigate the effects of citrus variety and age on the delivery efficacy of bactericides. This project requires a combination of greenhouse studies and field trials. Prior to conducting these experiments, a sensitive and accurate quantifying method of bactericides in citrus tissues is needed. This project officially started on December 1, 2018. This is the 7th quarterly progress report covering June 01 to August 31, 2020. During this period, we conducted and/or completed the following work/research tasks: 1) The samples from the foliar spraying experiments in greenhouse were analyzed. The preliminary results show that after foliar application, the concentration of oxytetracycline (OTC) and streptomycin (STR) decreased in the order of leaf > stem > root. Leaf concentration of the bactericides decreased with time, whereas their concentration in stem increased and reached peak at day 15. The concentration of antibiotics in the root was very low, only the STR was detected at day 7. 2) The samples from the treatments of trunk injection and root administration in the greenhouse experiments were all pretreated and are currently under analysis using the LC-MS, and hopefully we can obtain additional data by the end of September. 3) Preparations were made for field trials, including chemicals and tools for field applications of bactericides. The work planned for the next quarter (September 1, to November 30, 2020):The major research tasks for the next three months are to: 1) Analyze the data to be obtained and evaluate the delivery efficacy of three different application methods for bactericides in greenhouse experiments. 2) Implement field experiments, based on the greenhouse results, 3) Conduct treatments in fields, including foliar spraying, trunk injection and root administration.