Go and buy some Roseclear 3 and a sprayer to mix it up in - mix according to the dosage instructions on the bottle for fungal infections (stronger mix) and spray the plant (except any open flowers) thoroughly, underside and topside of the leaves, till run off. Do this on a non windy day and preferably at dusk when the bees have stopped working, and obviously not if its going to rain. And buy a good sprayer, not just a cheap little one, they're hard work!