Department of Crop and Soil Sciences - Cooperative Extension
Turfgrass Diseases
Pythium blight, Pythium aphanidermatum
Pythium blight, also known as grease spot and cottony blight, can be a highly destructive turfgrass disease, especially on bentgrasses and ryegrasses. Severe outbreaks can completely destroy the turfgrass within a few days if weather conditions favor disease development.
Symptoms and signs
Pythium blight first appears as small, irregularly shaped spots ranging from 1/2 to 4 inches in diameter. Leaves appear water-soaked in appearance at first, then shriveled. Diseased patches fade to a light brown or gray color. Groups of spots frequently join together. At times, the shape of the affected areas may resemble elongated streaks. Both the presence and pattern of these streaks seem to be determined by the flow or presence of surface water. 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.
Dense mycelium of Pythium aphanidermatum on tall fescue lawn.
Disease cycle
Pythium fungi may survive for long periods in the soil. 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. Disease development from the first infection centers occurs by growth of fungal mycelium and movement of spores from plant to plant. Under conditions favorable for disease development, Pythium blight can spread very rapidly.
Primarily a warm, wet weather disease, turf blighting and disease development will be most rapid and severe at air temperatures from 85° to 95° F. As the air temperature approaches 95° F, destruction of grass stands can occur in a very short time. Pythium blight develops more rapidly when nitrogen levels are high, and more slowly under moderate or low nitrogen fertilizer programs.
Cultural control
In problem areas, satisfactory plant growth maintained through moderate fertilizer applications provides the least risk of Pythium blight damage. Kentucky bluegrass, the fine fescues, and tall fescue are less susceptible to Pythium blight than perennial ryegrass and bentgrasses. Providing adequate water and air drainage, especially where susceptible grasses are grown, can help control this disease.
Chemical control
In the northeast United States, bentgrasses and ryegrasses may need fungicide protection. Timing of fungicides is important. If continued hot, wet weather is expected, the first spray should be applied as soon as symptoms develop. On high value turf, such as golf course putting greens, tees, and possibly fairways, preventative fungicide applications may be justified.
Red Thread, Laetisaria fuciformis and Pink Patch, Limonomyces roseipellis
Symptoms and signs
These two diseases present similar symptoms and appear as irregularly shaped patches of blighted grass. From a distance, affected areas have a reddish or pinkish cast. These diseases are usually restricted to the leaves, leaf sheaths, and stems, but in severe cases, may kill the entire plant. In the early stages of infection, symptoms appear as small blighted areas on leaves that enlarge rapidly to cover most of the leaf. Affected leaves dry out and fade to a bleached straw color. During moist weather, the leaves may become covered with the pink gelatinous growth of the causal fungi.
Symptoms and signs of red thread disease on perennial ryegrass.
Diagnosis of red thread is most certain in the advanced stages of disease development, when bright thread-like coral pink fungus mycelium, 1/16 to 1/4 inch in length, are produced at the tips of the affected leaves. In the case of pink patch, affected leaves are covered with the pink fluffy growth of the causal fungus.
Symptoms and signs of pink patch disease on perennial ryegrass.
Disease cycle
The fungi overwinter as a dried gelatinous mycelium covering on infected dead leaves or in clipping debris from previously infected plants. The fungi spread by transport of mycelium or infected leaves to new areas. The mycelium on living, infected plants are easily broken loose and transported mechanically. The fungus enters the leaves through natural openings and cut tips, and spreads rapidly through the remainder of the leaf. Red thread and pink patch diseases develop more readily when air temperatures are 65° to 75° F, with prolonged periods of rainy or humid weather. At times, the disease occurs in warmer, drier weather.
Cultural control
Where red thread or pink patch causes turf damage, maintenance of adequate nitrogen levels for turf growth usually will reduce the problem. Turf managers should be aware, however, that at high nitrogen levels other diseases, such as leaf spot and brown patch, may become damaging.
Chemical control
In most turf situations, these diseases are not sufficiently severe to warrant fungicide treatment. Occasionally, however, pure stands of ryegrass or fine fescues may become severely blighted during wet weather. In these instances, fungicide treatment will minimize symptoms.