I believe that my poor coleus plant is suffering a bout of powdery mildew. Until now, it's been a very healthy, robust plant. Lately, it is wilty and tinged with brown, in addition to little spots of mildew. So far, I've spritzed it with soapy water, and trimmed the diseased leaves that I found (but there are always more the next day). Does anybody have sure-fire cures? Is there a high chance of having to toss my poor baby away? That would break my heart, as it's the first plant I ever had success with.