It’s early in the gardening season and most plants are looking fresh and green. But the humidity in the air foreshadows what may come later in the summer. Powdery mildew is a fast-growing fungus that creates whitish patches on the leaves of many common plants. It regularly disfigures the monarda and zinnias in my garden. Pumpkins, winter squash, and other members of the cucumber family are also prone to this disease.
I find it much easier to tolerate a bit of mildew than to spray toxins, so I generally manage it by keeping the air circulating, avoiding overhead watering (especially in the evening) and looking the other way. But this treatment seems like something I might be willing to try.
Read about from someone with first hand experience here.