In my many years, I have had PM twice. I didn't properly learn my lesson the first time but believe I have now.
You have to purge. If a crop is close to the end, strip the bigger leaves, spray with H2O2 a couple times and harvest as soon as you can. Dispose of all soil. If a crop is young has shown signs of PM, get rid of it, start again, it will return if you don't. I think once a plant has had PM, it can then host it. You can't keep those around.
If you have plants that have not shown it and you want/need to keep, I have had very good success with a spray of 29% H2O2, mixed at 25mls per Litre. Every couple days, nice and clean, doesn't hurt the plants. Doesn't eradicate it but keeps plants from getting it until you purge any hosts out. Good to soak a plant down that has a lot of it before you start stripping the fan leaves and sending the spores out.
I've tried a multitude of products that don't work that well anyway. Some don't seem to work at all.
Powdery Mildew and spider mites are the two things to avoid at all costs where I'm from.