Without seeing those spots, I would guess at them being the signs of Downy Mildew.

But that's just a wild guess, particularly since I don't know what sort of temperatures you've been having. The marks can be anywhere from purply-red, to purple, to brown. Eventually that part of the cane is killed.

Could, of course, be something else entirely.

Jeri

Here is a link that might be useful: Downy Mildew information

Hi Jeri, thanks for that. I did a google image search and that certainly does look like the problem I have. The rose has been growing in really bad conditions, so I wonder if that has made it worse. It has been below freezing point quite a bit these last few weeks too.

Another possibility could be rose canker which affects rose canes.

Patrick

Here is a link that might be useful: rose canker

It probably depends on the cultivar of the rose, more than likely just cold.
If you get cold winters fungus would be dormant and wouldn't do any damage until early spring. Many roses get purple canes in the winter, or purple splotches. You can always spray them with a dormant oil, or copper
sulfate or lime-sulfur.