By the time August rolls around plant diseases can be in full glory.
Many diseases thrive in warm humid weather.
Black spot of roses is no exception. Black spot fungus, as its name implies, causes nearly circular, black leaf spots with fringed margins. It is usually seen on the upper leaf surface but may also appear on the underside of leaves. The spots may merge to create large, irregular lesions on the leaves. A yellow margin may appear on the leaves then the leaves quickly drop.