Most of the leaves infected with black spot will fall off - when they do, rake them up and dispose of them away from your garden compost, don't leave any on the ground. The time to prune these is spring, around early March, rather than now, although you can certainly remove any longer growths to prevent rocking. You will need to add topsoil or something to stop them rocking about, but try to make sure there are no leaves on the ground before you add the new soil. You can try the milk treatment - one part cow's milk to two parts water mixed in a spray bottle, spray thoroughly all parts, including under the leaves and stems, till run off. It probably won't do much at this end of the year, but next year, after pruning, use this mix and spray at the first hint of black spot. Can be used as often as you like - some people use the spray weekly throughout the growing season, starting before black spot arrives. Best with skim milk - gets more smelly in hot sun with full cream milk.