Warm days and cold nights are ideal for causing mildew on roses. Dryness at the roots and poor feeding can also cause mildew. It forms a pale grayish coating on the upper leaf surface and also on the buds. The infected leaves crumple and become distorted. One of the best ways to keep mildew under control is to keep good air circulation around the plants. Pruning to open up the center helps rose bushes Climbers on a closed wall may also not be getting enough air through them and should be pruned more open. Spraying with a fungicide at the first signs keeps mildew under control.
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