Pythium Blight Fungicides

Pythium blight is a fast-moving foliar disease that can destroy cool-season turf and new seedings during hot, humid, wet weather. Warm-season putting turf can also be affected during prolonged rainy or cloudy periods.

What to Look For

Small sunken greasy patches expand rapidly and may follow drainage or mowing patterns. Leaves become dark gray, orange, or brown and mat together; cottony white mycelium can appear in dew.

Why It Develops

Warm nights, continuously wet leaves, saturated soil, poor drainage, heavy nitrogen, dense seedlings, and equipment movement through wet disease favor spread.

Reduce Disease Pressure

• Improve drainage and avoid over-irrigation.
• Water early and minimize nighttime leaf wetness.
• Avoid heavy nitrogen during high-risk weather.
• Keep mowers and traffic out of active wet patches and clean equipment before entering healthy turf.

What University Research and Extension Guidance Says

NC State notes that disease can develop after several consecutive nights with long leaf-wetness periods and can spread very quickly. Penn State's 2025 phosphonate review supports preventive phosphonate use against Pythium but describes post-infection performance as weak. Rotate Pythium-active FRAC groups because resistance risk is significant for several chemistries.

Choosing and Using a Fungicide

Use the products below as a starting point, then match the active ingredient, FRAC group, turf species, use site, timing, rate, interval, and watering directions to the current product label. Preventive or very early applications are usually more reliable than rescue treatments after extensive injury. Rotate effective FRAC groups and combine fungicides with the cultural changes above.

Research and label note: University research may identify useful activity even when a current product label does not name this disease. That is research evidence, not a label direction. Apply a product only where the turf or application site and use pattern are permitted, and follow the complete label and applicable state requirements.

University sources: NC State Extension: Pythium Blight in Turf; Penn State Extension: Understanding Phosphonate Products.