That will do nothing. The spore is in the air. Sounds like you had a period of high humidity. The best way to prevent or control this next season is to spray your plants on a weekly basis with a ten(water) to one (milk) solution and that should take care of it. I saved my lilacs by doing this.....used one of those hand pump compressed air sprayers 2 gallon size. Be sure to rinse the bottle out so you don't get sour milk laying in it after use.

Hmm, the usual recipe for the milk treatment for powdery mildew is actually 9 parts water to one part cow's milk, not ten parts water, Loosestrife.

Otherwise, agree, it arrives on your plants, doesn't live in the ground, Kinangme.

Yes I put in the total by mistake, thanks.

Thanks Peeps....i was worried that the spore stays in the soil.... i've heard potassium bicarbonate dilute is also good.