It can really be very difficult to treat powdery mildew when it gets that advanced. There are literally spores everywhere. Success with any spray for PM requires treating and trying to get the plants dry again quickly so that new spores can’t proliferate. Honestly, I would probably dip the whole plant and then dry it with a fan quickly. Then do the next if you’re really trying to save it. But when PM is that advanced, it’s going to be tough to beat. If you have access to the genetics, it might be best to start over. Clean everything with bleach and treat preventatively from the gate. You could try adding other remedies into the mix – sulfur for instance. But I think the best that you can hope for is to keep it as minimal and under control as you can. When you are done, clean everything with bleach.