Identifying and Managing Leaf Spots on Black-Eyed Susans: Fungus or Something Else?

Black Spots on Rudbeckia: Getting to the Root of the Problem

"Brown-eyed Susan" usually refers to Rudbeckia triloba, while "black-eyed Susan" is Rudbeckia hirta. Both can develop black leaf spots, but the cause must be identified before treatment.

Key Questions for Diagnosis

• What is the Latin name of your plant? (Check the tag or describe flower details.)
• Are the spots raised (insect galls) or flat (fungal)?
• Do spots appear on flowers or only leaves?
• Are plants in pots or ground?

Common Causes

• Fungal leaf spot (e.g., Septoria): flat, dark spots with yellow halos; favored by wet foliage.
• Insect damage: flea beetles or other chewers leave tiny holes, not spots.

Management

If fungal, water at the base, remove infected leaves, and apply a copper-based fungicide. Annual spraying is not always necessary if cultural conditions are improved. Thinning crowded plants in spring reduces humidity and disease pressure.

Accurate identification ensures you treat the right problem and avoid unnecessary chemicals.