I've grown Austins here in Kansas since the mid 80's. Our climate is extremely hot and mostly dry in the summer, with wildly varying temps through the winter. I don't spray for blackspot or anything else, and the Austins perform better for me than any other group of roses. The Austin website lists many currently for sale that are thornless or nearly so.
This past summer we did have unusual high humidity, and all the hybrid tea roses had some blackspot. The Austins had the very least, but I don't plant them close to one another, and we do have quite a bit of wind. Ive toured gardens in Oklahoma where it is humid, and the Austins were most excellent there. I have over 100 of them; the garden I saw in Oklahoma had probably 300.
Hope that helps!
Austin roses are my favorite, but I do recognize that they don't grow perfectly everywhere. Most have incredible perfume, so that's a great selling point for me.
