Abstract: When planting trees, all of branches and tip of trunk from 1/3 of top ofone year-old part were cut off. As a result of surface reducing of trunk,branches and leaves, the water-consumption in the treatment was less than inthe contrast. Furthermore, the number and total length of roots were increased. So that the relative water content in the treatment was higher than inthe contrast. The results reveal that the poplar trees canker disease caused by Dothiorella gregaria was reduced with relative water content increased. Theeffect of controlling is about 60%.

Key words: Poplar canker, Cut top, Principles of diseases control