Posted: 29/01/2017 at 10:19
Does it get enough water? It's planted very close to the wall, which will help to keep it dry. It can't absorb fertiliser if it's too dry. So I'd do what others have said. Cut out the oldest woody stems, weed around the base, give it some rose food, lightly worked into the soil, give it a good water, mulch it and don't let the soil get too dry. I would also be inclined to use a fungicide, anti-fungus only - not a pesticide which is harmful to wildlife.