Aspirin is the remedy for fungal plant problems, Black spot, powdery mildew, and rust are a terrible trio of fungi, which can attack and destroy your plants. Scientists have found that two uncoated aspirin tablets (325 milligrams each) dissolved in 1 quart of water and used as a foliar spray can thwart these diseases. I have not tried this, but I will.
Spray for control of powdery mildew on squash I have used a solution of milk, baking soda, and liquid dish detergent to effectively control powdery mildew in my own vegetable garden. Here is the spray recipe I use: Fill the 32 oz bottle with 1/2 c. of milk. Add 2 T. of baking soda. Fill sprayer with water & add one drop of liquid dish detergent. Mix contents well