One thing that I had to do on a grow once was use potassium bicarbonate spray to control pm in my last few weeks of flower. It makes the ph on the surface of leaves unfavorable to pm and it will keep it at bay for a little bit.
I would carefully remove most of the affected leaves, spray them with the bicarbonate and pray. Lol
The bicarbonate from what I read is ok to use in flower (heck, I did) but I didn’t spray the last week before harvest.
Additionally if you so choose, you can h202 rinse your flowers after cutting right before you hang and dry.
You’re not going to be able to kill it off, but you can try to control it until harvest to try and save your girls.
Plant health and room health are two causes of pm. Look at the affected plants and see if you notice anything like too much or too little air flow, too much humidity, crowded (or under trimmed plants) too high of temperature swings, etc.
Pm is everywhere, but normally healthy plants will not get pm provided the room conditions are good.
My pm was from overcrowding and not enough air flow. (Had an overly hot humid spot in my room)
Once I kept up on my pruning and added some more fans, they held back the pm till harvest. Only 2 of my 12 got it. That bicarbonate helped me in the last few weeks of flower. I would of cried if I had to chop and start over....