If you have powdery Mildew a good simple and cheap and most of all organic curative is.....milk. Mix one part of milk with 20 parts of water, spray once a week and you have solved your problem. Also a good preventative.
Have a good day, Erik van Rees Vellinga
Many thanks for your tip, Erik. Milk is indeed an excellent organic spray for mildew, as is whey.