If it’s not greenfly attacking your precious roses it’s this fungus. Rose Blackspot is a serious fungal disease of roses which mainly affect the leaves which break out into blackish, brownish or purplish spots or blotches on the upper surface of the leaf. Diffuse and radiating strands of the fungus can sometimes be visible. It may also appear as small, black scabby lesions on young stems.
Rose Blackspot can affect all kinds of roses. It spreads rapidly through the plant and can infect others, and can ultimately weaken the rose. Usually the infected leaves turn yellow and drop off, and a whole rose can be affected this way. The fungus produces spores which are released in wet conditions and is usually spread by rain-splash.
Seen spring onwards. The spores overwinter. Found where roses are found in the wild, or in parks and gardens. Very common and widespread, affecting both wild and cultivated roses.