Fungicides need to be applied at the first sign of powdery mildew. Powdery mildew is most severe in heavily shaded areas. Avoid such locations when planting roses or other plants susceptible to mildew, i.e., lilac, zinnia, dahlias. Follow suggestions for good air circulation as outlined under blackspot. Galls are most frequently seen as round, rough-surfaced growths near the plant's crown or on roots.
Crown gall is a difficult disease to control once a plant is infected.
It is best to rogue diseased plants as soon as they are detected. Where possible, remove and discard all soil in which the root system is growing and replace with sterilized soil. If crown gall is a recurring problem in an area of your yard, it is best to rotate the area with a nonsusceptible grass crop for 3 or 4 years. Where a gall is restricted to stem tissue only, cut off the entire cane and immediately seal the cut surface with pruning paint. Always sterilize cutting tools with rubbing alcohol after each cut .