Powdery mildew looks like a white, dusty mold that is growing on your zucchini squash leaves. It is a common problem for plants from the Cucurbitaceae family. Produced by several species of fungus, the infection spreads quickly over large distances. You don't need to use any pesticides if you want an organic solution to the problem.
Things You'll Need
Remove the badly infected leaves and those that are clearly dead. Don't put them on your compost pile, as the mold spores could survive in the soil and infect the next year's crop.
Mix 1 part skim milk with 1 part water. Spray the mixture on the all the zucchini leaves and let it dry.
You can also use a mixture of 1 oz. baking soda in 1 gallon water. Another recipe recommends the use of 4 tbsp. baking soda, mixed with 1 gallon of water and 2 1/2 tbsp. horticultural oil.
Repeat the treatment every few days. Keep it up even after the mold is gone to keep it from coming back. It can also be used as a preventative measure.