How do I get rid of powdery mildew on my plants?

You see it as white, floury patches, usually on the upper leaf surface. Bag the removed leaves before carrying them out so spores do not spread. Then thin out dense foliage, add a clip fan, and avoid big swings between a humid night and a dry day, which mildew likes.

Treatments are regulated and what is allowed differs by country, so check the label and local rules before using anything, and stay off the plants once flowers have formed. Prevention is far easier: a clean tent, steady airflow and a dehumidifier where needed. For options see pest control and biological control.