Black spot of rose, also known as leaf blotch, and leaf spot, is a disease caused by a fungus called Diplocarpon rosae. The optimal conditions for disease development are 75-85° F and high relative humidity. Infection may be greatest on leaves that remain wet for six hours or longer. Leaves and canes can become infected.
Signs and Symptoms
Leaf symptoms are roundish, black spots with fringed margins that can be up to ½" in diameter. The spots form on the upper sides of leaves. The tissue surrounding the spots turns yellow. Infected leaves may prematurely drop from the plant. Usually lower leaves are infected first. Excessive leaf drop weakens the plant, predisposing it to other forms of injury such as those caused by temperature extremes. Cane symptoms are blister-like, reddish-purple blotches that later turn black.
Black spot is caused by the fungus Diplocarpon rosae. The fungus
Type of Sample Needed for Diagnosis and Confirmation
Collect 3 to 5 leaves and flowers attached to petioles. For further information go to Sample Collection
Management of black spot includes sound cultural practices such as raking fallen leaves and removing infected canes. Avoid wetting leaves when watering and maintain air circulation around and within the plants to promote drying.