Powdery mildew shows up when the days are warm and dry, and the nights are cool and humid, but without dew. It is a fungus, and the spores need humidity, but no free water, to germinate. There are several organic remedies: I favor a baking soda and soap solution, while others favor diluted milk.

Thank you very much i'm going to try a weak soap solution :O) x

Soap by itself doesn't help much, though. I use a mix of 1 tablespoon organic dish soap and 2 teaspoons of baking soda in a gallon of water.

oh ok thank you Tugbrethil can you tell I haven't got a clue what i'm doing ? :o(

Don't feel blue! I've been gardening for over 40 years--mostly learning the hard way! : }