The purpose if 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, which is helpful to provide potential solution to the development of effective chemotherapeutic tools for HLB management. Three application methods, foliar spraying, tree trunk injection and root administration, for bactericides (oxytetracycline and streptomycin) currently suggested to be used in citrus HLB management have been employed in this study with greenhouse and field tests. The data obtained in the test will be used to: 1) compare the delivery efficacy of the bactericides applied by the three application methods into the citrus plants; 2) to compare the distributions and concentrations of the bactericides in different citrus tissues and; 3) to compare the effect of citrus variety and age on the delivery of bactericides applied by the three methods and up taken concentrations of bactericides by the plants. This project officially started on December 1 2018. This is the 9th quarterly progress report covering December 1, 2020 to February 28, 2021. During this period, we have conducted and/or completed the following work/research tasks:1) Field study has been completed based on greenhouse study results. The study included two citrus varieties, Grapefruit and Valencia orange, in two farms located in the Fort Pierce area. Oxytetracycline and streptomycin applied into/onto citrus plants by foliage spraying, tree trunk-injection and root administration methods. Samples of citrus leaves, stems, roots and fruits from all the tested plants collected on the day 0, 7, 15 and 30 after treatments and brought back to the Lab for processing. 2) All the samples collected from the field study have been processed for extraction of oxytetracycline and streptomycin analysis purpose. The procedure used for the extraction of oxytetracycline and streptomycin included washing, air drying, cutting, liquid nitrogen grinding, weighing out, and solvent extracting, SPE column cleaning up nitrogen-air dying and bring up to targeting volume with special solvent for HLPC-MASS analysis. 3) The extracted samples for oxytetracycline and streptomycin analysis have been sent to cooperated institute, the Citrus Research and Education Center (CREC), UF for analysis purpose. However, the analysis has not been finished yet. The work planned for the next quarter (March 1 to May 31, 2021): The major research tasks for the next three months include: 1) Completing the analyses of the extracted samples 2) Processing of the data from the field trials.3) Write the final report for this project.4) Preparation of manuscripts from the data obtained from the greenhouse and field experiments..