Common Lawn Diseases: Identify and Treat

Spot the Problem Before It Spreads

Lawn diseases can destroy large areas of turf in days if left untreated. Early identification is your best defense. Here are the most common lawn diseases and how to handle each one.

Brown Patch

Appearance: Circular brown patches 6 inches to 3 feet across, often with a darker "smoke ring" border. Grass blades have water-soaked lesions.

Cause: Rhizoctonia fungus thrives in hot, humid weather with poor drainage. Most common in tall fescue and ryegrass lawns during July–August.

Treatment: Apply a fungicide containing azoxystrobin or propiconazole. Improve drainage and reduce evening watering. Remove excess thatch.

Dollar Spot

Appearance: Small, silver-dollar-sized bleached spots scattered across the lawn. Individual grass blades show hourglass-shaped lesions.

Cause: Low nitrogen levels combined with dew and temperatures between 60–75°F. Most common on Kentucky bluegrass and bentgrass.

Treatment: Apply nitrogen fertilizer to close existing spots. Fungicides with chlorothalonil prevent new infections. Mow when grass is dry to avoid spreading spores.

Pythium Blight

Appearance: Greasy, water-soaked patches that quickly turn brown and collapse. In early morning, affected areas may show white cottony mycelium.

Cause: Pythium fungus in hot, humid conditions with poor drainage. One of the fastest-spreading lawn diseases — can destroy an entire lawn in 24 hours.

Treatment: Improve drainage immediately. Apply mefenoxam or propamocarb fungicide. Avoid watering in the evening. Remove and replace severely damaged areas.

Leaf Spot and Melting Out

Appearance: Small dark spots on individual grass blades that expand and merge. In the "melting out" phase, entire plants die from the crown down.

Cause: Bipolaris and Drechslera fungi. Triggered by frequent light watering and excessive nitrogen.

Treatment: Water deeply and infrequently. Apply fungicide containing iprodione. Reduce nitrogen applications during active infection.

Prevention Checklist

• Mow at the correct height for your grass type
• Water deeply in the morning, not evening
• Remove clippings during active disease periods
• Core aerate annually to reduce thatch
• Maintain proper soil pH (6.0–7.0 for most grasses)