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 March 1,to May 31, 2021 During this period, we have conducted and/or completed the following work/research tasks: 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..