It's been raining off and on for the last 10 days. Now the leaves of some of my plants look as though I have powdered them with flour. I'm afraid this is some type of fungus that I can do nothing about. This stuff just seem to spring up over night. I know it's not the regular fungus that starts at the bottom of the plant and works its way upward. This stuff is white. It's not causing the leaves to yellow or turn brown. A local garden shop said it was spidermites. But I'm not sure what that looks like. Any suggestions?