Pythium Blight, Cottony Blight, Greasy Spot (fungus – Pythium aphanidermatum)
Host Grass: Hybrid Bermuda(Cynodon dactylon), Common Bermuda, Bentgrass(Agrostis palustris), Fescue, Perennial Ryegrass(Lolium perenne), Poa Series(Poa sp.)
Cause and Symptoms: Disease is favored during rainy, foggy weather and in low lying areas where air circulation is poor. Roundish, dark, greasy to slimy patches of matted grass, from two to 12 inches in diameter, appear suddenly. On close-cut turf, pythium blight may appear as streaks that follow water drainage or mowing patterns. When disease is very active, fungal mycelium grows profusely over affected plants so that diseased areas have a cotton-like appearance. Hybrid bermudas are more susceptible to pythium than common bermudagrass. Pythium may cause seedling blight and poor stand development in perennial ryegrass overseedings. It also can cause crown and root rots which generally occur in early spring or late fall when soils are cool and excessively wet or saturated. Symptoms of Pythium root rot mimic melting out and anthracnose and there is no foliar mycelium.
Control and Management: Diagnosis should be confirmed by a diagnostic laboratory as soon as possible. Good water management is critical. Avoid late day watering and overwatering new plantings. Remove thatch with frequent verticutting and avoid overfertilization. Improve soil drainage and aeration. Increase air movement by reducing shading, selective pruning or fans. Increasing the mowing height and other practices that promote root growth may lessen the damage from Pythium root rot. During extended periods of warm, humid weather, a preventive fungicide program is advised. Fungicide control of Pythium root rot is less consistent than control of foliar blight. If extensive damage appears, turf seldom responds to fungicide treatment (See the section Chemical Controls for Turfgrass Diseases).
Content edited by: Young-ki Jo, firstname.lastname@example.org , Assistant Professor and Extension Specialist, Dept Plant Pathology & Microbiology, Texas A&M University, Texas AgriLife Extension Service, May 31, 2013