The Chicago Botanical Gardens did one of their trials on asters and rated them by both PM and rust resistance. https://www.chicagobotanic.org/downloads/planteval_notes/no36_asters.pdf

Surprisingly, there are a quite a number of different cultivars that are rated as 'excellent' wrt to powdery milder resistance. Fortunately, all 3 of the asters I grow - Monch, Eurybia divaricata (white wood aster) and Symphytotricum ericoides (calico aster) - are all very highly rated and I have never had any issues.

Symphyotrichum ericoides is Heath Aster, Symphyotrichum lateriflorum is Calico Aster.😁

I have used Aster laevis Calliope for projects and in my own garden. (dont know the current term, sorry)

it does spread abit, so it needs strong neighbours like Panicum or Miscanthus, but you can pull out single stems easily, height about 4 - 5 feet

I garden in a z7 with dry, warm summer, on loam,

this beauty is upright in full sun on rather lean soil

and the foliage is still immaculate even though we had a shitty fungus-y season with lots of rain earlier

with roses, tomatoes, squash, potatoes wilting with all sorts of mildew/ fungus