With Powdery Mildew don't only focus on treating the plants, figure out where it's coming from and treat the entire grow space if possible.. Clean clean clean.
I moved a bunch of old christmas boxes and clothes, old hockey gear etc into a storage unit for $20/mo then bleach washed my walls, floors, tools, pots, trays, fans, everything possible. Haven't had PM since and I was fighting it for a solid year. It wouldn't come up then randomly 2-3 weeks into bloom the mid canopy would be infected.
The only completely effective spray with zero residues I've used was BiosafeSystems Zerotol in a Hudson fogger with full PPE on. I literally fogged every fucking square millimeter of my grow rooms top to bottom corner to corner edge to edge SOAKING it all! Ceilings, floors, walls, fans, filters, pots, pans, stakes, netting, EVERYTHING. That shit requires serious protective equipment though it is stabilized highly concentrated hydrogen peroxide (h2o2).
If you just spray your plants your going to have PM come back, you're only protecting the plants from an existing inevitable issue. The real thing that needs to be done is the spores need to be destroyed in the room and then strict practices need to be put in place to keep it from coming back.
Another huge huge tip is buy some shoes/slippers that are strictly used in your grow space, do not wear outside shoes or walk into your grow after being at the hydro shop. You're likely to track in bullshit from other peoples dirty grows.
