Ez, are you sure it's powdery mildew? My eyes aren't so good....
If you're sure it is, man go in and turn off that fan!!
PM spores are HIGHLY mobile, if you have PM you're blowing it's babies all over your plants!
I've never treated it on mj, but I understand both milk or vinegar can help in a pinch.
I'll be back shortly, hang in there!