Pretty near all of my older varieties seemed to be mildew-prone until I figured out the timing for feeding and how to water. Now I dump a wheelbarrow load of fresh compost around them just after that huge and fast vegetative spurt that happens just before bud-set. At that time I'll also spray them once or twice with seaweed emulsion. If I need to water, I just lay an open hose at the base...no overhead watering. That's it. I haven't had mildew problems since.
The newer cultivars I've added in the past few years don't seem to be quite as vigorous; plants grow more slowly, and bloom stalks are fewer...but then again, they're still fairly young.
Judy,
If you'd like to try a couple of these, just shoot me a Treemail and I'll mark them for you.