Southern Blight on Black-Eyed Susan: Diagnosis and Soil Management

The blackened stems and sudden collapse of your black-eyed Susans (Rudbeckia) point to Southern blight (Rhizoctonia solani), a soil-borne fungus that rots stems at the soil line, especially in wet, poorly drained conditions.

Immediate Action

• Remove and destroy affected plants (don't compost).
• Improve drainage: amend heavy clay with compost, expanded shale, or grit.
• Raise the bed if water pools after rain.

Long-Term Fix

Lift healthy plants, thoroughly amend the entire bed with coarse organic matter and mineral aggregates to create a well-drained profile, then replant. Southern blight persists in soil, but it only kills when conditions favor it—saturated soil and heat.

Prevention

• Space plants for air circulation.
• Mulch with pine straw, not heavy wood chips (holds moisture at crowns).
• Water at soil level, not overhead.
• Rotate with resistant species (ornamental grasses, salvias).

Fix the drainage, and the fungus becomes a non-issue.