Get some Serenade and spray the plants. Serenade is safe to use up until the day of harvest, but it stinks to high heavens so you wouldn't really want to. Since you are a week or two from harvest, it'll be okay to use it now. Usually one application will kill the powdery mildew.

Not that it makes much difference now, but you should be running your lights at night, when the temps drop and you need the heat.

PC