Abstract: Objective The aim of this study was to clarify the action mechanism of tusite on Duranta repens cv.Gold leaves inoculated with Cuscutajapouica Choisy,and provide reference for controlling C.japouica.MethodPartial physiological indexes of C.japouica and D.repens seedlings 7 d after spraying tusite AS of different concentrations (6,10and 14 ml/L).ResultAfter treated by 6,10 and 14 ml/L tusite,superoxide dismutase(SOD) activity and soluble protein content of C.japouica significantly decreased (P<0.05,the same below),which were 28.34%,38.73%,58.68% and 67.37%,39.62%,71.05% of those in control (clear water).The content of soluble sugar and the activities of peroxidase (POD) and catalase (CAT) were significantly higher than those in control.After treated by 6% tusite AS,chlorophyll fluorescence parameter,photosynthetic parameter,content of soluble protein,content of soluble sugars and activities of protective enzymes(SOD,CAT and POD) ofD.repens were significantly higher than those in control.The chlorophyll a and chlorophyll b contents were significantly higher than control in 6 ml/L 6% tusite treatment,and were 1.35 and 1.53 times of those in control.But there were no significant difference in chlorophyll a and chlorophyll b contents between other treatments and control (P>0.05).Conclusion 6 % tusite AS controls C.japouica by affecting metabolism of protein and other biomacromolecules and destroying the balance of protective enzyme in C.japouica.On the contrary,the host plant,D.repens,can prevent injury from tusite through remaining high level of photosynthesis,increasing the content of soluble protein and keeping the balance of protective enzyme.