Abstract: Based on the results of occurrence，damage and control index of Liberobacter asiaticum from 2002 to 2006，the dynamic trend and trajectory model of the occurrence Liberobacter asiaticum in citrus orchards were discussed．The correlation equation between the amount of citrus psylla per tree and the infection rate of citrus psylla was m=0．0302Mp一0．1145(n=9，r=0．9771**)．The correlation equation between the infection rate of citrus psylla and the infection plant rate of Liberobacter asiaticum was P=0．8960 Mp一4．5754(n=36，r=0．9479**)．The correlation equation between the infection rate of citrus psylla and the incidence rate of Liberobacter asiaticum was D=0．5085P+3．5167(n=7，r=0．7507**). The relationship between the infection rate of Liberobacter asiaticum and yielding loss rate has been investigated，showing Y=3．1469P一0．5354(n=6，r=0．9979**). Based on the allowable economic level，the statistic control index of Liberobacter asiaticum was 1．0％ of the incidence rate and early warning index was 4％ of the infection rate of citrus psylla．It was suggested that early shooting stage of citrus trees(spring shoots，summer shoots，autumn shoots)was all optimum control period for citrus psylla．The control index was 0．1 citrus psylla per tree(efective pest amount of 5 shoots on eastern，western，southern，northern，central branches)．It was shown that the applied control index was in accordance with the practical situation．

Key words: citrus, Liberobacter asiaticum, citrus psylla, occurrence, control index