Water, water them. Then spray with 1 tsp soda in a quart of water. Did you remove the lower foot of foliage for better air circulation? The lower leaves snap easily right off the stalk especially in early a.m. or evening. The good news is that I don't think mildew hurts the plant any, just unsightly. At least that's what I recall.

You can spray them with the same thing that you spray your roses with. We frequently use the Rose Pride stuff on our dahlias.

This year, the powdery mildew is HORRIBLE in my area. I have seen it on so many different plants all over town. I tried a solution of 3 parts water to one part milk - it worked amazingly well...went out to spray again a week later, and noticed all kinds of lush new growth, and a huge decrease in the mildew. I have treated twice, and now it's pretty much all gone. Maybe give it a shot?

Michele