Abstract: 1. On the crape myrtle, there are three species of powdery mildews——Uncinuliella australfana(basionym:Uncinula australiana),Erysiphe lageratroemiae and Phyllactinia corylea. Under an identification on powdery mildew infected on the crape myrtle, the species existing in Kunming area Should be Uncinuliella australiana, the same specieswith the powdery mildew of the crape myrtle in Yaan City. 2. Under the bud scale, the mycelium of powdery mildew will be able to pass through winter, or the suitable condition is given, the mycelial filaments will develop and primary infection will take place on the host. 3. The spread of the conidia is affected by precipitation, temperature, relative humidity and the suitable speed of wind. It is evident that precipitation is unfavo-rable for the spreading of the conidia. The spread of the eonidia has obvious diurnal rhythm. 4. In spring, as temperature rises, the bud of the host sprouts. The mycelial filaments begin to infect the host, and induce the disease. In the rainy season(from June to September), epidemic of the disease rises on high and ends in the later fall.