Do your research.
That doesn't look like any powdery mildew I've ever seen, it usually appears in small rounds spots that look a tadbit like a layer of a cotton ball.
What that looks like to me is either, thrips or the beginning of mites, but more like a very mild
infestation ofthrips. Try looking at it under a scope see if you see something.
Also is the whole plant affected? or just the top? bottom?