QuestionsHow to growRosesWeeds, Pests and Diseasesmildew 0 Vote Up Vote Down denis galavan asked 14 years ago I have mildew on most of my roses some gardeners say not enough water others say too much water can you tell me the cause? 1 Answers 0 Vote Up Vote Down Gerry Daly Staff answered 7 years ago Roses generally suffer powdery mildew in dry spots, usually close to a wall, and if they have soft growth. Spray with Roseclear.