Insecticidal Soap Spray
An organic insecticidal soap spray can be purchased from any garden center or made up for any spare clean spray bottle. You can simply drop a bar of castile soap into water overnight. If you have unscented, liquid castile soap, you add a tablespoon of liquid soap to a quart of water. You can also add 1-2 tablespoons of oil to help coat leaves more effectively.
Spray the leaves lightly on both sides. Spray again after rain. It is a good idea to try the spray out on a couple of leaves to make sure you aren't doing any harm and have your proportions correct.
Mix 1 tablespoon potassium bicarbonate and ½ teaspoon liquid castile soap (not detergent) in 1 gallon of water. Spray liberally to all affected areas. Apply once a week for three to four weeks.
This solution acts both as a treatment of existing powdery mildew infections and as a preventative measure.
Diatomaceous earth can be used to treat flea beetles. It is a white powdery substance and you should wear a mask when treating your plants with it.
Neem oil can be used to treat flea and cucumber beetles, as well as powdery mildew.
BT Bacillus can be used to treat tomato hornworms.
Serenade Disease Control
Serenade can also be used to combat powdery mildew.