A common disease on roses in Minnesota is black spot [1]. This fungal disease is most severe in wet years and is spread by splashing rain throughout the growing season. A symptom of this disease is circular black spots with feathery margins on the upper leaf surface. Occasionally, yellow rings surround these spots. Infected leaves eventually turn yellow [2] and fall from the plant. Excessive defoliation may weaken plants, making them more susceptible to cankers and winter injury. Canes may also be infected with stem lesions appearing red to purple in color.

Black spot management should begin with good cultural practices. Maintain plant health by properly watering and fertilizing plants. To reduce the number of spring infections, prune out infected canes [2] and dispose of all plant debris, including leaves after the growing season.

To limit the number of infections during the growing season, minimize water splash by mulching around the base of plants and watering at ground level. Fungicides may also be needed as a protective treatment during rainy periods or for severely infected plants.

Fungicide application generally begins in early summer with the development of leaf spots. A variety of fungicides are currently labeled for black spot. Carefully read the label before buying, opening, and using fungicides.