Reduce infection by keeping the area around the bush free of debris. Prune out and destroy diseased canes and leaves. Do not plant roses in shaded spots, especially areas which dry out slowly. Thin roses to open up the plant center so air can freely circulate through the foliage. Irrigate early in the morning to preven the disease and avoid irrigating at night, especially with sprinklers.
New growth is especially susceptible to mildew during hot, dry periods.
If the disease does appear and requires a fungicide, thoroughly cover the canes and leaves with the dust or spray. They occur on wounds caused by pruning or budding. Gall tissues have no definite growth pattern. The bacteria may live for several years in the soil or on another host before infesting roses. If bacteria is in the soil, replace it with new soil.