That's not powdery mildew.
Looks more like mite bites.
Inspect the underside of each leaf with a 10 to 30X magnifying glass.
Also looks a bit like over-spray so if you see no mites you should be alright.

Amazing for the wattage, brah.

Subscribed,
Weezard.
Weezard Reviewed by Weezard on . My Single 3W LED A-Train Grow I see so many baby plants vegged under big HID lights or like 5-6 or more 23w or larger CLFs or a 90-120W LED, when that is hardly necessary. And then the same people talk about GPW... People did not believe the huge plant I vegged with a single 23w CFL, yet this is way more impressive. It is all about not wasting light. Here is my widdle 8" X 8" A-Train vegged under a single 3w cool white LED. Yes, one 3W light with nothing else. The hull wouldn't come off and it was nearly dead and I Rating: 5