Powdery mildew

I use anti-mildew microbes. My favorite is Trichoderma harzianum. Mix it and spray. Trichoderma harzianum does not survive long above the ground. For mildew, usually takes only one dose. But then, if this strain has a weakness for white powder mildew, I would worry about bud rot later on. And I do use trichoderma much more to prevent bud rot during the final month of flowering. Spray frequency is once a week. More often if it rain. (I grow out door in tropical Asia. And once in a while, I use have secondary type of microbe just to keep the bad mold from evolving. Bacillus subtilis works for me. I also use microbes for thrips and spider mites.

yup looks like WPM. Is it appearing on the lower leaves? you may have good airflow in you grow space, but if you are flowering in 50%, i guarantee its more humid between all those leaves and buds. to prevent issues with mold (especially during autumn when the air is super humid from where i come from) I defoliate almost all my indoor grows and use a fan to ensure proper air circulation. this way i can be sure i get good airflow in between all the plants. Outdoor grows i have been mixing milk with water which i spray onto the leaves. i have heard it helps prevent mold, but i haven't ever had the time to actually test this, but there is a lot of info online that supports this method. anyway now that you have it, you have to try and spot every bit of it and get rid of it so it doesn't spread. mildew on leaves you can wipe off with a wet towel or rag. if you have any of it on your buds, i would get rid of them to ensure there is no more spores helping the mold spread. Then ensure you have good airflow and then treat the plants. some people use backing soda others purchase a commercial product for mold control. since i haven't had any issues before with WPM, ill let someone else with more experience say what they think is the best way to treat it.

Take off infected leaves. Spot treat areas that cant be removed. A light defoliation of leaves laying on each other would benefit air flow and stop the spread and growth of more powdery mildew.

Spot treating with a solution of 1 pint of water 5 tbsp h2o2 3 drops of Palmolive dish soap

I'm growing Autoflowers Coco/perlite 18/6 7ml micro 10ml bloom 4ml calmag per gallon