What is your preventative regime?
Cleanliness is most important, second only to proper quarantine of anything brought into my grow. I try to never leave my space without making sure it's absolutely clean. I diffuse essential plant oils to kill airborne mold/mildew/viruses, and discourage bugs from entering the facility. I treat my plants once a week with OGBioWar Foliar pack. I also hit them one time in Veg with
Green Cleaner or Mite and Mildew wash (formerly Quantum Apolcalypse
Neem oil) and once right at the flip. I also take great pains to make sure the room environment is always dialed in to the seasonal weather changes, and temperatures do not fluctuate extremely.
The last 2 years this regimen has successfully prevented powdery mildew in my grow, in spite of the fact that it was all over the trees and plants outside my house.
This is just what has worked for me. I'm sure there are folks out there who can do it cheaper. I don't mind spending some money for peace of mind, lol!