Potassium bicarbonate– Similar to baking soda, this has the unique advantage of actually eliminating powdery mildew once it’s there. Potassium bicarbonate is a contact fungicide which kills the powdery mildew spores quickly. In addition, it’s approved for use in organic growing.
Milk – The latest player in the fight against powdery mildew is milk. It’s not clear yet why it works so well, but it is believed that naturally occurring compounds in the milk are at work to combat the disease while also boosting the plant’s immune system. One experiment showed good results by applying a weekly dose of one part milk to two parts water.