I have powdery mildew on my petunias. We have had a very humid hot summer and when you water large flower planters everything gets wet. I live along a lake so there is that humidity to deal with as well. What can I do to get rid of it? My orchids are very close by and I don't want them infected. I have one that is just starting to bloom after two years. It got flattened in a hail storm.