Downy mildew thrives in cool, wet weather. Downy mildew can kill canes so rapidly that they wilt overnight. Botrytis, a gray mold, attacks buds and flowers. There is no cure for rose mosaic, a viral disease. The viral disease rose rosette is spread by mites.
Galls can grow on the stem, root or crown of the plant.
Canker can spread down or around the stem, causing dieback. Dr. Alan Windham, plant-disease expert with the University of Tennessee Agricultural Extension Service, shares some tips for identifying and coping with common rose diseases. Fungal diseases are influenced by climate, so some are more prevalent in different parts of the country. Blackspot, a widespread fungal disease, is indicated by dark circular spots with ragged edges. Generally, any spot on rose foliage is a sign of fungus disease.