Powdery mildew is a widespread disease of roses. The disease is easily recognized by the white powdery appearance of infected leaves, twigs, and flower buds. Infected leaves may also appear distorted and fall from the plant.
Powdery mildew is favored when rainfall is low or absent, temperatures are between 70 and 80, nighttime relative humidity is high, and daytime relative humidity is low. Mildew spores can spread easily by wind to nearby healthy plants.
To control powdery mildew:
- Select powdery mildew resistant roses for planting.
- Do not crowd plants.
- Plant roses in full sunlight.
- Prune infected canes and rake and discard mildewed leaves and flowers during and after the growing season.
- Adequately fertilize roses to maintain plant vigor, but avoid excess fertilization.
- Apply a labeled fungicide (many are available at garden centers) at the first sign of mildew. Follow label instructions for rates and timing.
This article originally appeared in the July 14, 1995 issue, p. 104.