I am finding the beginnings of powdery mildew spots on my aster leaves. What's the best way to treat the plant for this?
Powdery mildew, at the early stages, can be halted by spraying with plain water to wash off fungal spores before they can germinate. Also, applications of neem have proven to be a good preventer and maybe a cure of PM.
Baking soda + water is supposed to work on powdery mildew (haven't tried it myself). Otherwise, Daconil works great on powdery mildew.