The Roses in your garden may be putting on a lot of fresh growth. To ensure this keeps clean, you need to start spraying the foliage with a suitable fungicide to help prevent the disease black spot from affecting your plants this year.
When growing roses it is wise to spray at regular fornightly intervals, using a different fungacide each time throughout the season so the disease doesn't build up a resistance to one chemical. You will also need a regular spraying program starting from now with an insecticide to keep any aphids at bay. Whenever spraying please remember to always read the instruction label carefully before use and spray early in the mornings or in the evenings, and not in bright sunshine.