Well mine don't, Jonathan, because they're down to the ground, but I did notice last week that the foliage I cut off had a light dusting of mildew. Wouldn't hurt to spray if you want to retain the foliage, or its newly growing.

Hi Bamboo. Do you chop yours right back? That must make watering easier too. Is rose fungicide suitable spray?

Yea, that'll do fine, J - there's a lot of mildew about this year, it's all over my Verbenas currently.