I also have a rose showing a couple of canes like yours. I thought if pruning cuts were painted it would prevent it the insect from laying eggs in the freshly cut pith area. Now I read it is a fungus and I need to spray with a fungicide? 2nd call for help.

Normally, canker is not something that you "get" and then it spreads uncontrollably unless treated. The spores are always around and can infect wounds during cool, damp weather, so you lose an occasional cane. It is part of rose gardening. Usually the canker spot will be contained by the rose's immune system and will become inactive, leaving a patch of dead bark. However, some roses are particularly susceptible. I discarded 'Brass Band' because it was canker-ridden in our climate. Maybe 'Charles de Gaulle' is one such, but I have not grown it. I would be tempted to give that plant a severe pruning once it cools off and good zone 10 growing weather develops. I'm not sure that's the best course, however.

Iris_gal, not sure what your question is. I don't worry about the little bees and wasps that drill in fresh-cut pith. The young do not eat the rose tissue. The tunnel is just a nursery chamber where the adults feed the larvae on aphids or pollen they have gathered. I usually prune out the tunnels during spring pruning, but thick canes with tunnels can continue to support growth for a season or more.

Thanks Michael. My misinformation was that dead canes were because eggs were laid in exposed pith and the hatched larvae ate downwards causing the cane to die. And that this was called canker.
'Paradise' had 3 dead canes this summer when I pulled out/cut back annuals . That many got me worried. I found this online:

"...cankers start as small yellowish or reddish spots on the bark, gradually increasing in size. Eventually, the canker turns brown, increases in size, and may eventually girdle the cane."

Maybe there are other reasons for cane death. I didn't notice spots on the canes and saw no girdle_ing.

"Girdle" just means the bark dies all the way around the cane, so the cane dies above that spot. If the bark is killed only halfway around, the cane will survive and support some growth and bloom.

There are borers that tunnel way down the cane, but these do not start with drilling the fresh-cut pith at a priming cut. Google "raspberry horntail." Nests of the pith-drillers ("small carpenter bee") are usually 2" deep, although once in 35 years I found a deep tunnel.

Canker is a fungal infection and there are several kinds. Dormant sprays of sulfur or lime sulfur can help with one kind, but its not worth the trouble IMO.

Thanks Michael. I have a better understanding now.