Black spot of rose is probably the most common disease of roses in the landscape. Symptoms: Leaf spots form on the leaves and enlarge into large, dark circles with irregular margins. Several spots may grow together. As spots increase on a leaf surface, the leaf generally turns yellow, then falls prematurely. In addition, similar dark lesions form on twigs and rose hips. Infected plants are stunted with unsightly foliage and produce fewer, paler flowers. A severely infected plant may be entirely defoliated by midsummer. Cause: Infection is by spores that form on fallen leaves and on stem lesions in spring. Spores are rain splashed and infect leaves that remain wet for over 8 hours, so disease is most severe following prolonged wet and warm spring weather. During summer, spores are capable of causing secondary infections in wet weather. Control: If black spot is severe, drastically prune back rose wood to within 1 to 2 inches of the bud union in the fall or early spring, according to variety and cultivars. Remove and bury or burn all canes. Hand pick, if practical, infected leaves as they appear, particularly in spring and early summer. Courtesy: Horticulture Extension, MSU