Pythium Root Rot Fungicides

Pythium root rot is a water-related root disease that can occur in any season when soil remains saturated for several days or weeks.

What to Look For

Turf turns yellow or orange in irregular areas and may follow drainage patterns. Roots, crowns, stolons, or rhizomes become dark and greasy, and root depth and density decline sharply.

Why It Develops

Poor drainage, over-irrigation, extended rain, excess thatch and organic matter, shade, and low air movement create the low-oxygen conditions that favor infection.

Reduce Disease Pressure

• Correct chronic drainage and reduce over-irrigation.
• Aerify and topdress regularly to manage organic matter.
• Increase light and airflow where practical.
• Reconstruct persistently wet root zones when drainage cannot be corrected culturally.

What University Research and Extension Guidance Says

NC State recommends preventive 14- to 21-day programs on chronic sites during prolonged wet weather and says curative programs may require a sequence of Pythium-active chemistries. Root-targeted products should be watered in as directed. Penn State notes that phosphonates are strong preventively but relatively weak after infection is established.

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 Root Rot in Turf; Penn State Extension: Understanding Phosphonate Products.