M. rosae produces black spots of about two to 12 mm in
diameter usually in the upper surface of the leaves (Fig.
1a). Often, those spots may have irregular, radiate, feathery
borders (Fig. 1b). In older lesions, black spore-bearing
structures, called acervuli, can be observed as well as white,
slimy masses of conidia (Fig. 2a). Yellowing around the
lesions on infected leaves can occur, and severe defoliation
occurs in the most susceptible cultivars. While leaves
are the most susceptible part of the plant, stipules and
pedicels can also be infected. Spots can also be found also
in peduncles, fruits, and sepals. Symptoms of black spot are
usually confused with those of Cercospora leaf spot (See
EDIS publication Cercospora Leaf Spot of Rose at http://edis.
ifas.ufl.edu/PP267)