Diagnosing and Managing Brown Patch and Dollar Spot: Why Fungicides Fail and Culture Works

SE Michigan lawn: suspected brown patch/dollar spot, conflicting advice, fungicide in hand but reluctant. Used 12-12-12. The fix is cultural, not chemical.

Get a Real Diagnosis

Take samples to your MSU Extension office (canr.msu.edu). They identify the pathogen—critical because management differs.

Why Fungicides Fail

• Preventive only—don't cure active infections.
• Kill beneficial fungi that suppress pathogens.
• Create resistance.

Cultural Management That Works

1. Water at midday so grass dries fast (reduces leaf wetness).
2. Stop synthetic fertilizer. Use compost/humus topdressing.
3. Topdress with non-sterilized aged manure/compost—introduces antagonist microbes.
4. Mow high (3.5–4 inches).
5. Improve air flow (prune surrounding vegetation).

Fungus is managed by environment, not eradicated by poison. Change the conditions, and the disease retreats.