Lawn fungus identification guide (with treatment for each)

Lawn fungus thrives in high humidity, warm nights, poor air circulation, and stressed grass. Here are the five most common diseases in the Mid-Atlantic.

Brown patch

Large irregular circles 6-24 inches across with a darker smoke ring at the edge, visible in morning dew. Hits when nights stay above 68 degrees. Treatment: reduce watering, mow taller, apply fungicide. Do not apply nitrogen during an active outbreak.

Dollar spot

Small straw-colored spots 2-6 inches across with hourglass-shaped lesions on individual blades. Appears when nitrogen is low and dew lingers. Treatment: apply nitrogen fertilizer. Water in the morning so grass dries during the day.

Red thread

Pink or red thread-like strands on blade tips in cool, wet spring weather. Low nitrogen is usually the cause. Treatment: fertilize. The grass outgrows it in a couple of weeks. Fungicide is rarely needed.

Rust

Orange powder on blades that rubs off on shoes. Appears in late summer on slow-growing turf. Treatment: fertilize, mow regularly, water adequately. Resolves on its own in fall.

Pythium blight

The most aggressive — greasy, dark, matted patches that spread overnight in hot, humid conditions. Requires immediate fungicide. Improve drainage and never water in the evening.

Not sure which fungus you have? Scan your lawn with Grasslytics for an AI-powered diagnosis with specific treatment steps.