Personally I'd prune and see how it does and if you are not happy remove next year.

If a general anti fungal hasn't worked you might try Roseclear, which is a specific for black spot. Once you clear that it might sprout again - some plants are very resiliant.
(unless Sbg thinks differently, in which case listen to her...)

I agree try roseclear. many plants will recover well. worth giving it a go in my opinion.

Thanks all.... will try the pruning route first...then Roseclear.