Rosemary Leaf Spot: Fungal Culprits and Organic Fixes

White-Centered Leaf Spots on Rosemary = Likely Fungal

Rosemary (Salvia rosmarinus) with bright white spot centers surrounded by dark margins suggests Cercospora, Alternaria, or Septoria leaf spot. Favored by wet foliage, cool nights, and deep planting.

Immediate Actions

1. Remove & destroy infected leaves. Do not compost.
2. Improve airflow: Space plants, prune dense growth.
3. Water at base only: Drip irrigation or careful hand-watering.
4. Check planting depth: Crown should be at soil level. If buried, gently excavate.

Fungicide Options (Herb-Safe)

• Copper fungicide (copper octanoate or hydroxide): Organic, broad-spectrum. Spray every 7–10 days.
• Bordeaux mixture: 4-4-50 (copper sulfate + lime). Homemade, effective.
• Baking soda spray: 1 tbsp baking soda + 1 tbsp light oil (e.g., canola) per gallon water. Spray every 3–4 days. Raises leaf pH, inhibits fungi.
• Potassium bicarbonate (GreenCure, MilStop): More effective than baking soda, less phytotoxic.

Cultural Notes

• Rosemary hates wet feet. Gritty, alkaline soil. Full sun.
• Avoid high nitrogen—promotes soft, susceptible growth.
• Few fungicides are labeled for herbs; copper and bicarbs are safest.

New growth should emerge clean. If not, submit sample to extension lab for precise ID.