University of Maryland Extension

Black Spot - Roses

small black spots on rose foliage
Photo: Black spot on rose

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Black spot (blackspot) is the most important fungal disease of roses worldwide. The initial symptoms start as feathery-edged, black spots on lower leaves. As these spots enlarge, the leaves turn yellow and drop off. The disease continues up the stems until the entire plant becomes defoliated. Stem lesions are less obvious but start as dark, irregular blotches that eventually become blistered. Stem lesions are the most important source of fungal spores for initiation of the infection cycle next season.

The disease is caused by the fungal pathogen Diplocarpon rosae. Leaves are most susceptible when young and must usually be moist overnight before infection can occur. The disease can be spread by rain, dew, irrigation, people, insects, and transport of infected plants. The fungus cannot live in the soil or last on pruning tools for longer than a month. Black spot spores can survive in fallen leaves and stem lesions over the winter and will remain active year round on the plant in mild climates.

Management strategies: Sanitation is critical for black spot management. Removal of fallen leaves and pruning infected canes will dramatically slow initial spring infections. Good air circulation will reduce the incidence of black spot by promoting faster drying of leaf surfaces. Restrict irrigation during cloudy, humid weather. Rose cultivars resistant to black spot are increasingly more available, but resistance can be regionally variable. Most people will need to use labeled fungicide sprays every 7-14 days as the first leaves emerge in the spring through the fall for adequate control of this disease.

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