Does mildew hurt peonies or phlox? If so, how to remove it.
Powdery Mildew has a long term result on a plant, but short term it doesn't have bad results.
It can be prevented by good hygine, picking up fallen leaves each winter. Also, do not spray water on the plant except in early morning. Once on the plant little can be done to remove it. You can limit its growth on the plant, spray with a milk and water mixture and remove leaves that are heavily affected. Do not compost these leaves. A one to ten ratio of milk to water works well. Use whole milk or unhomogenizes if available.