Black Spots on Black-Eyed Susan Leaves: Fungal Leaf Spot Diagnosis and Management

Your black-eyed Susans (Rudbeckia) have blackened foliage, and you're also asking about deadheading yellow daylilies. Let's tackle the fungal issue first—it's the primary concern.

What's Causing the Black Leaves?

Almost certainly a fungal leaf spot—common culprits are Septoria rudbeckiae or Cercospora species. Symptoms: small, dark brown to black spots with yellow halos, expanding to blotches, often starting on lower leaves and moving up. Favored by:

• Wet foliage (overhead watering, rain splash)
• Crowded plants with poor air circulation
• Humid, warm weather

Immediate Actions

1. Remove and destroy severely affected leaves (don't compost).
2. Switch to drip irrigation or water at soil level only.
3. Thin crowded clumps to improve airflow.
4. Apply a copper-based fungicide or neem oil preventatively on new growth (follow label).

Prevention for Next Year

• Clean up all foliage in fall—fungus overwinters on debris.
• Space plants 18–24 inches apart at planting.
• Rotate planting areas if possible.
• Choose resistant cultivars like 'Goldsturm' (though not immune).

On Deadheading Yellow Daylilies

Yes—snap off each spent flower (including the ovary) daily. Cut finished scapes to the ground. This encourages rebloom on repeat varieties and keeps plants tidy. It won't hurt non-rebloomers either.

Note: Black-eyed Susans prefer hot, dry, well-drained conditions. If your site is damp or shady, consider moving them.