Sorry to hear you’re seeing some PM. I’ve been battling this shit chronically for months now. Defol is definitely important, as well as airflow. If you’re just seeing a bit pluck any infected leaves and maybe try a light hydrogen peroxide spray .I forget the amount of h2o2 tbh but there’s tons of recipes online. Use a small amount of wetting agent and be sure to spray the entire plant top to bottom.
If it persists the only thing I found that worked that I could spray in flower (if hp doesn’t work) is potassium bicarbonate. I used it at (I believe) 3tbsp per gallon with a tbsp of veg oil and a tsp of dish soap.
Keep in mind this WILL burn the pistils on the plant and seems to effect yield a bit. The bud is safe to smoke, but I still would wash them at harvest just to be sure. You’ll need to spray again weekly while they’re flowering or it will come right back.
Going forward you’ll need to extra vigilant and keep an eye out for any signs of it. I found a sulfur spray worked great in veg, and hitting them with it just before they formed flowers kept it at bay for a while. The only thing is after several applications the plants started growing like mutants from the sulfur so use it sparingly if possible.
Also keep in mind that some strains are more resistant than others, so if you don’t see it showing up on your NL it probably has resistance and you should dump the WW.
There are lots of expensive sprays that are supposedly effective but I never tried as the cost was too high to use all the time. I started a PM thread that was basically inconclusive, but there’s lots of info and suggestions:
Good luck and hopefully you can kill it, I HATE powdery mildew.