There are propriotory sprays you can get from any Garden Centre. Start a regime of spraying when the first leaves are about to open. Follow the instructions on the bottle.

Make sure you have collected up any leaves or bits of stem that have fallen on the ground below your roses - this wll help stop it spreading to the new growth.

Agree with Amble & Roger, pick up any diseased leaves & start regular spraying from when shoots start to estabish.