I have never heard of daylilies getting powerdy mildew. However you can cure it using a systemic fungicide. You want a systemic because that way you don't have to be as concerned that you covered every inch (top and bottom) of every leaf in order to cure it. I use Bonide (brand name) Systemic Desease Control For Roses Flowers and Shrubs. I actually have lots of roses and that is what I spray them with. I also use it on my zinnias and anything else that gets fungus or mildew. It is a fungicide only.
