I also have lots of rust on my roses this year. It's the first time it's been this bad, and I haven't quite pinned down the cause. In the past, it would show up on one or two OGR's scattered around the garden, and I just assumed they had no disease resistance. This year it's on a lot of modern roses that have never exhibited it before. Some of them are in crowded beds, but others aren't, so crowding doesn't seem to be the issue here. Humidity isn't the issue here either. The only thing different about this year is the combination of the ongoing drought and the lack of frost this past winter. Maybe that produced the ideal breeding ground for rust, but I'm not sure. I'm stumped.
