Studies on the Occurence, Development and Control of Rosa roxburghii Powdery Mildew

Powdery Mildew of Rosa roxburghii Tratt.is caused by Sphaero-theca pannosa (Wallr.) Lev.,cleistothecium has not been yet discovered in Xian.Hypha overwinters in the bud scale as primary infection source.Conidia are disseminated by wind.The incubation period is about 4~5 days.The disease occurs in the middle of April,2 peaks of the disease occur in May~June and September~October.The factors affecting the disease occurence are temperature and relative humidity.The disease can be controlled by 25% Triadimefon.Chemicals such as 50% Topsin,Antimycin 120 and Antibiotic Bo-10 also showed a certain degree of control efficiency.