Could it be sunburn if it is at the tips?

Whatever it is, it's hideous! Hopefully this picture will help...

I don't think it is sunburn. I think that might just be what my Lamarque got last Fall. I worried it was Downy Mildew, but I ended up thinking it was black spot because the plant did not die. I put horse manure around it per Jeri's advice. The plant got trimmed back this Spring and seems to be coming along well. I think the "infection"did weaken it somewhat, and the Spring trimming was some yellowish canes and foliage that looked pale. The new growth this Fall looks great. I wish you luck with your plant.

I'd love to see closer shots of the leaves with spots. What I can see looks like blackspot, but . . .
The discoloration on the stems, by contrast, looks a lot like Downy Mildew to me. If it is, the spots will turn grey -- necrotic -- as the tissue is killed. I've never seen blackspot do that to the canes. (But blackspot isn't a big deal here, so maybe I just wouldn't know.
Has it been warm/damp there? That would favor downy.
You COULD probably have samples tested, so you know for sure.
If it IS Downy, yes, I would mulch with nice, fresh horse manure.

Hi all, poor MIP might now have a bigger problem: roundup damage or Possibly RRD. I am seeing thready growth that looks like one or the other. I sprayed roundup near that rose 2 months ago, but used a box to keep the drift from traveling. I only just tonight read that roundup can stay in the soil and be absorbed by the roots. MIP is a big girl and her roots probably do reach that sprayed area.

At least I hope it's roundup and not RRD.