Paclo, avid, eagle 20.
Do your research before using what people recommend to you.
10000% do not spray Promis, Paclobutrazol, Avid,
One of my biggest fuck ups was bringing autoflower plants outside and inside everyday, into a room with other plants. Aphids, powdery mildew and other fun critters over everything. Cleaned like a mofo still lost a crop to powdery mildew well after it all, did a insane deep clean and now I'm mega careful about that kind of stuff. Even accepting clones from friends is generally a no-no. Everything gets bleached between runs now, and blasted with UV then peroxide after. Lamps fans pots cords. Anything in that tent is getting cleaned before a next run goes in.
General rule. She goes outside..
She stays outside
These days you need a sealed grow room unless the air coming in is HEPA filtered for pollen etc.. I run a totally sealed grow with co2 supplementation and mini-split unit for heating & cooling. (Heating is only in Jan-Feb where I live where it gets negative °F)
Do not accept Clones from anyone or cuttings ideally use seeds for genetics. I quit taking clones last year and since bleaching my entire room I haven't had PM since. I also keep my Humidity below 50% throughout flower. 43-46% RH and haven't seen PM since.
If you CLEAN everything and ozone the space or sulfur burn you can eliminate it. It's the spores that blow around and land on leaves and re-infect. If you believe it is systemic go ahead and throw the plants away, bleach the entire room and start fresh.
Powdery Mildew can be coming from old boxes, board games and cloth, carpet, porous objects etc..