A friend from France who is on the iris Cubit forum once posted this recipe for a treatment for powdery mildew. I've never tried it, because usually when I get it here the growing season is pretty much over. Maybe someone might want to try it and see if it works.
Baking Soda Spray:
1 tbsp vegetable oil
1 gallon unchlorinated water
1 tbsp apple cider vinegar
1 tsp Listerine (yes, the famous mouthwash, not mint flavour, just regular)
1 tbsp liquid soap
1 ½ tbsp baking soda
Pump sprayer (large)
