On high value turf, such as golf course putting greens, tees, and possibly fairways, preventative fungicide applications may be justified. If continued hot, wet weather is expected, the first spray should be applied as soon as symptoms develop. Providing adequate water and air drainage, especially where susceptible grasses are grown, can help control this disease. Kentucky bluegrass, the fine fescues, and tall fescue are less susceptible to Pythium blight than perennial ryegrass and bentgrasses. In problem areas, satisfactory plant growth maintained through moderate fertilizer applications provides the least risk of Pythium blight damage. Pythium blight develops more rapidly when nitrogen levels are high, and more slowly under moderate or low nitrogen fertilizer programs. As the air temperature approaches 35° C, destruction of grass stands can occur in a very short time. Primarily a warm, wet weather disease, turf blighting and disease development will be most rapid and severe at air temperatures from 30° to 35° C. Under conditions favorable for disease development, Pythium blight can spread very rapidly. Disease development from the first infection centers occurs by growth of fungal mycelium and movement of spores from plant to plant. In turf with a past history of Pythium blight, infected plant debris from the previous season or fungus spores in the soil are sources of infection. Pythium fungi may survive for long periods in the soil. With high humidity in early morning or throughout the day, diseased leaves may be covered with the white, cobwebby, moldlike growth of the causal fungus. Both the presence and pattern of these streaks seem to be determined by the flow or presence of surface water. At times, the shape of the affected areas may resemble elongated streaks. Groups of spots frequently join together. Diseased patches fade to a light brown or gray color. Leaves appear water-soaked in appearance at first, then shriveled. Pythium blight first appears as small, irregularly shaped spots ranging from 10-100mm in diameter. Severe outbreaks can completely destroy the turfgrass within a few days if weather conditions favor disease development. If extensive damage appears, turf seldom responds to fungicide treatment (See the section Chemical Controls for Turfgrass Diseases).Pythium blight, also known as grease spot and cottony blight, can be a highly destructive turfgrass disease, especially on bentgrasses and ryegrasses. Fungicide control of Pythium root rot is less consistent than control of foliar blight. During extended periods of warm, humid weather, a preventive fungicide program is advised. Increasing the mowing height and other practices that promote root growth may lessen the damage from Pythium root rot. Increase air movement by reducing shading, selective pruning or fans. Remove thatch with frequent verticutting and avoid overfertilization. While Pythium root rot is caused by several different species of Pythium with different temperature optima cool to hot, Phytophthora blight is only favored by hot weather. Avoid late day watering and overwatering new plantings. Heavy rains early in the planting season favor both Pythium root rot and Phytophthora blight. Symptoms of Pythium root rot mimic melting out and anthracnose and there is no foliar mycelium.Ĭontrol and Management: Diagnosis should be confirmed by a diagnostic laboratory as soon as possible. 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. Pythium may cause seedling blight and poor stand development in perennial ryegrass overseedings. Hybrid bermudas are more susceptible to pythium than common bermudagrass. When disease is very active, fungal mycelium grows profusely over affected plants so that diseased areas have a cotton-like appearance. On close-cut turf, pythium blight may appear as streaks that follow water drainage or mowing patterns.
Roundish, dark, greasy to slimy patches of matted grass, from two to 12 inches in diameter, appear suddenly.
#Pythium blight series#
Host Grass: Hybrid Bermuda( Cynodon dactylon), Common Bermuda, Bentgrass( Agrostis palustris), Fescue, Perennial Ryegrass (Lolium perenne), Poa Series (Poa sp.)Ĭause and Sym p toms: Disease is favored during rainy, foggy weather and in low lying areas where air circulation is poor. Pythium Blight, Cottony Blight, Greasy Spot (fungus – Pythium aphanidermatum )
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