The condition you describe sounds like rose canker fungus. Prune the rose canes back to where you get a good whiteish colored center pith of the canes. Seal the ends of the canes with white Elmer's glue or Tacky Glue from a craft store. Then spray the canes area and soil around them with a good fungicide such as Immunox or another good fungicide of choice. If the rosebush is healthy it will usually overcome the canker fungus with just a little help. Be sure to wipe your pruners off with a Clorox or Lysol Wipe after each pruning cut on the blackend canes so as not to spread the problem to other canes or rosebushes. Here is a link to an article with more information to help you if it is rose canker:
https://www.gardeningknowhow.com/ornamental/flowers/roses/rose-canker-fungus.htm
Keep the roses well watered and fed. Even give them some water with a product called Super Thrive in it. It helps the rosebush deal with the stress of a fungal attack and other stresses. Water them two or three times with the Super Thrive in the water, you can add some water soluable fertilizer in it too.
