Black Spot on roses is caused by which pathogen?

• A. Pseudomonas syringae
• B. Botrytis cinerea
• C. Phytophthora infestans
• D. Diplocarpon rosae

Answer: (D)

Black spot on roses is caused by a fungal pathogen named Diplocarpon rosae. This disease shows up as small, round to irregular black spots on the upper leaf surface, often with a yellow halo, and these spots can merge as the leaf yellows and eventually drops. The fungus survives in infected fallen leaves and plant debris, so keeping the area clean and removing fallen leaves helps reduce the source of new infections. It spreads helped by wet, humid conditions and leaf wetness, so air movement and avoiding overhead watering are important practices. Management focuses on sanitation and cultural controls—remove and destroy affected leaves, prune to improve air circulation, water at soil level rather than over the foliage, and apply fungicides if necessary. Other organisms listed are responsible for different diseases: Botrytis cinerea causes gray mold, Phytophthora infestans causes late blight, and Pseudomonas syringae is a bacterial pathogen that leads to other types of leaf spots or blights.