"If you are seeing powdery-looking patches on the foliage of your plants, you most likely have a case of the very common powdery mildew fungal disease. Here is a simple spray for controlling the spread of the fungus. It won't get rid of the fungus on leaves that already have it, but it will prevent it from spreading to the rest of the plant." Farming & Agriculture
Prevent powdery mildew with this spray: 1 gallon of water 1 tablespoon of baking soda 1 tablespoon of vegetable oil 1 tablespoon of dishwashing liquid Mix the ingredients together and add them to a spray bottle. Spray your plants weekly, preferably on overcast days to prevent it from burning the foliage.