Greetings. I'm hoping to get suggestions as to what to use to kill powdery mildew. It came on strong and spread fast. I burned all of my mature plants and kept two small plants in hopes of saving them. The mildew is coming back. I'm not sure I trust the dude at the grow store anymore because I think the mildew came from the dirt I bought there. So I'm asking for suggestions on what to use to kill it. Thank you in advance!