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Red Thread and Pink Patch

Laetisaria fuciformis and 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.

Red Thread

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 ¼ 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.

Pink Patch

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. Fungi enter leaves through natural openings and cut tips, and spread 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 such cases fungicide treatment will minimize symptoms.