Pythium Root Dysfunction Fungicides

Pythium root dysfunction is primarily a disease of young creeping bentgrass putting greens. Roots are infected during cool weather, but the damage often becomes visible during summer heat or drought.

What to Look For

Circular or irregular patches up to about two feet across first appear wilted or nutrient deficient, then turn orange and thin. Infected roots are tan, lack root hairs, and release sand easily from a soil probe.

Why It Develops

Root infection is favored when mean soil temperatures are about 50–75°F. Summer heat, drought, low fertility, low oxygen, young sand-based root zones, and shallow rooting expose the earlier damage.

Reduce Disease Pressure

• Maintain adequate fertility and use soil and tissue testing.
• Raise summer mowing height above severe stress levels.
• Use surfactants and hand watering to maintain uniform moisture without saturation.
• Aerify and topdress to improve oxygen and manage organic matter.

What University Research and Extension Guidance Says

NC State recommends preventive programs during fall and spring infection windows rather than waiting for summer symptoms. Its program guidance also distinguishes products that should be watered into roots from phosphonate combinations that are retained on foliage, so placement must follow the specific label and research-supported program.

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 Dysfunction in Turf; Penn State Extension: Understanding Phosphonate Products.