The milk is a fungicide, that means kills the fungus. Baking soda + light oil is a deterrent. You're right about dampness encouraging the growth of powdery mildew, but in Alan's dry climate, "damp" is meaningless. Margaret L >Maybe there's different kinds elsewhere, but the powdery mildews that grow >here in TN thrive in both hot humid weather as well as cold damp weather. >Putting water on the plant infected with it is like throwing gas on a fire. > >As I understand it, the milk solution (as well as baking soda, sulfer, or >even the fungicide I use) just deters further reproduction of the mildew >somehow. It don't actually kill it, supposedly. > >Dan Dixon