Can anyone advise me on what is turning out to be a serious problem. My rambling roses (David Austin's Open Arms and The Lady of the Lake) appear to be in terminal decline. What I thought was a bad case of black spot, looks on inspection much worse. Not only are most of the leaves affected and falling off, but most of the stems are either yellowing, brown or split from the base up. Do I need to take drastic action to get on top of this. I've included a photo, which hopefully shows some of the effects I'm talking about.