With high humidity, warm days and nights and rain, powdery mildew typically comes and takes hold on your cucumber, squash and zucchini leaves. It looks like small white powdery dots all over the leaves. They will grow in size and cover the entire leaf. Treatment with 1 tablespoon of baking soda in 1 gallon of water is very effective. The video shows you what an early outbreak of the fungus look like.
Add dish soap to help the baking soda stick to the leaves as well as kill soft bodied insects. Spray around 6 pm.