I Have Treated My Peony For Mildew With Your Homemade Solution. Will I Have To Repeat After A Rainfall Or Watering?

Question

It is a new plant, not yet mature. It was planted in full sun mid-summer and thrived, but now is in part sun as fall arrives. It has just now developed the mildew problem.

Answer 1

Any homemade or organic treatment will need to be applied, regularly, until the problem subsides. Even without rainfall, I would still apply once every few days until there is no more powdery mildew.

If this is, in fact, downy mildew rather than powdery mildew, you will want to continue treatment. It is quite a bit more aggressive than powdery mildew, and will do damage unlike powdery mildew that it simply disturbing, visually.