Prune infected areas out of your shrubs at the first sign of infection. Cut away any infected branches or leaves and dispose of them away from any plants or shrubs. Dip the shears in a bucket containing a mixture of one part bleach to four parts water to disinfect after each cut, so that you do not spread the fungus.
Apply fungicidal soap to the affected shrub. This soap, available at many nurseries and garden centers, will help to prevent the spread of the disease but is safe for plants, animals and humans. Follow application instructions for your particular product.
Mix one teaspoon of baking soda for every one quart of water in a spray bottle. Spray onto the shrubs once per week to prevent the spread of powdery mildew.
Apply a sulfur-based fungicide to your shrubs every seven to 10 days to protect healthy shrubs from contracting powdery mildew. These fungicides are available at most garden centers or nurseries.