powdery mildew

Look what I found at Rebecca's Garden... a recipe for Powdery Mildew tonic.
One tablespoon of baking soda
2 teaspoons of vegetable oil
Add to 1 gallon of water.
Mix it very carefully and thoroughly. Put it in a spray bottle, and you’re ready to go. This helps prevent the spread of powdery mildew. But if you want to keep it from developing in the first place, start early in the season, spraying on a weekly basis.