Don't cut them back now. You won't get any blooms this year and it will really weaken the plant. Some of my other fall aster get bad mildew late in the summer, but still bloom. I don't think Alma ever has though. Why are you afraid to use fungicide? Most chemicals are safe to use if used properly or Google for some alternative remedies using household products. Kevin

Shelley, This morning I almost asked on here if the PM debacle that followed the Easter Freeze had reappeared in any gardens as the roses passed through that same temperature range going into fall. I decided not posting that question might be less tempting to fate (a sort of cyber head ducking). I have no answer for you, but I intend to do some preventative spraying (if possible) to see if it will help. So...thanks for posting the problem. So far, it hasn't repeated down here. Even on the roses that were so PM laden this spring.

NE, "3. Some plants don't like wet leaves and preferred to be watered under their leaves. The wet leaves can mildew." A common misconception about Powdery Mildew is that PM is promoted by wet leaves. That misconception is so widespread that it is now almost an urban myth. Many supposedly authoritative books say that wet foliage promotes Powdery Mildew. Wet foliage does promote many foliage diseases, but not Powdery Mildew. Apparently most garden writers refer to the works of other garden writers and this has become a glaring example of the hazards of "Group Think". The truth is that Powdery Mildew spores cannot germinate in water and that water prevents it. Powdery Mildew grows on dry leaves. Refer to the National Gardening Association's Q&A on Powdery Mildew on Zinnias in which they say, "Powdery mildew is unique among common plant diseases in that it doesn't require a wet leaf surface to spread. It can thus thrive during hot, dry weather, which is why you see it appearing in August. The general advice to inhibit the spread of fungal diseases is to avoid wetting leaf surfaces. In the case of powdery mildew, you can actually inhibit infection with frequent sprays of water." Considering all the books and other publications that are wrong on this subject, and how widespread this urban myth actually is, its going to take a lot of effort to correct this deeply rooted misconception about Powdery Mildew. I am giving it a shot here, but it's a shot in the dark. ZM

That's interesting about there being plant specific... Nature is fun. I was just going to the extreme to stress the point that I think the important word would be "delay" vs "prevent" with pm. I have one planting of an older variant of phlox and pm always gets it early right as it starts to bloom. I remove the entire plant to the ground fairly early each year.... But it always hits the exact same time the next year. I have no other phlox and I live in a garden desert in my subdivision... I don't think a single home I pass in and out of the neighborhood has anything besides the original landscaped plants.... Non being phlox. The only other perennial that gets pm for me was an old peony... Which got the axe because of it. And then of course the late season squash get it. so to the original poster... Given your circumstances ..... And this isn't a plant that you are passionate about enough to put up with tight cultural practices.... And ...You would only being delaying the inevitable maybe a bit later in the season....(as others bring up.)....Looking into a replacement species would probably work better for you.