Pink Patch & Red Thread on Lawns

Creeping red fescue and perennial rye are the most susceptible

By: Sandy Feather 2011
Penn State Extension

Q. My lawn has had red thread in the past, but I have not used a fungicide to treat it because when I read the labels, they recommend treating every 30 days and these products are expensive. The lawn has always rebounded without treatment, but I fear it may not this year because the fungus has taken over so much of the lawn. I understand the wet weather is making red thread worse, and the long range forecast predicts wetter-than-normal weather until July. Do you have any suggestions?

A. Red thread (Laetisaria fuciformis) is epidemic throughout Pennsylvania due to the very wet spring we are having. Grass that is stressed or growing slowly due to low fertility, cold weather or other diseases is most susceptible. This fungal disease is most severe on perennial ryegrass and creeping red fescue, although all lawn grasses can be affected when conditions favor disease development. It often appears with another disease called pink patch, Limonomyces roseipellis. 

Disease Symptoms on your Lawn

Both diseases have similar symptoms. The causal fungi overwinter on dead blades of grass or clipping debris from last season. Air temperatures of 65 to 75F and rainy or humid weather favor the development of red thread and pink patch. Red thread and pink patch are spread on turf equipment and by foot traffic.


Irregular, circular patches of affected grass have a reddish or pink cast when seen from a distance. Affected leaf blades dry out and take on a bleached out straw color. Distinct symptoms appear as the diseases progress. For red thread, reddish, thread-like fungal mycelium extends from the tip of infected blades of grass. Pink patch appears like pink cotton candy coating infected blades of grass. These last two symptoms are most obvious when the grass is wet with dew.

Seeing pink or red?
Pink Patch
Pink Patch with 'pink cotton candy'
Red Thread
Red Thread with reddish thread-like fungal mycelium

Plant pathologists use a device known as the plant disease triangle to describe the conditions required for a given disease to develop. These conditions include the susceptible host (creeping red fescue, perennial ryegrass), the disease-causing agent (causal fungi, Laetisaria fuciformis,), and the correct environmental conditions (67-75 degrees F, rain), over a period of time. All three legs of the triangle must be present for red thread to develop.

Managing Plant Diseases

Managing plant diseases involves interrupting one or more of the legs of the triangle. The use of resistant varieties of grasses disrupts disease development by removing the susceptible host. Cultural controls such as raising the mowing height, watering deeply and infrequently, maintaining a balanced level of fertility, periodic dethatching, and core aeration to alleviate soil compaction disrupt some of the environmental conditions required for red thread to develop. Finally, the use of fungicides disrupts the causal fungi.

Cultural controls include maintaining adequate fertility levels; red thread and pink patch can be indicative of low fertility. Be careful to use a moderate amount of nitrogen, one-half to one pound of nitrogen per thousand square feet. Too much nitrogen can create favorable conditions for other, more serious diseases such as leaf spot to develop. Raise the mowing height to three inches, and avoid mowing when the grass is wet. While that can be challenging when we have rain so frequently, mowing wet grass is one of the best ways to spread red thread throughout your lawn.


Video of Pink Patch and Red Thread

Lawns in the Shade

Lawns with low maintenance practices


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