Red Thread is a common lawn disease

Resistant varieties of grass disrupt this lawn disease

By: Sandy Feather 2009
Penn State Extension

Q. My creeping red fescue lawn gets red thread every year. I use fungicides and fertilize to help it grow out, but it comes back every year. Is there anything I can do to get rid of it once and for all?

A. The only way for you to get rid of it once and for all is to completely renovate your lawn to get rid of the susceptible creeping red fescue and replace it with a variety of grass that is resistant to red thread.

Plant pathologists use a device known as the plant disease triangle to describe the conditions required for a given disease to develop.

Red Thread Development Conditions

These conditions include the susceptible host (creeping red fescue), 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 lawn 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.

Red Thread Disease
Classic red thread disease symptoms
are most visible in early morning

Red thread is most severe on perennial ryegrass and fine fescues. It often appears with another disease called pink patch, Limonomyces roseipellis. 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.


Spreading the Disease

Red thread and pink patch are spread on turf equipment and by foot traffic. From a distance, affected patches of grass have a reddish or pink cast. 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.

Cultural Control

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.
Overseeding or replacing susceptible grasses with resistant varieties is helpful in controlling these diseases. Resistant varieties of perennial ryegrass include Assure, Derby Supreme, Gettysburg, Legacy, Loretta, Pinnacle, Regal and Sherwood.


Fungicide Applications for Red Thread?

While home lawns rarely warrant fungicide applications to control red thread, it may be necessary when lawns are composed of pure stands of perennials ryegrass or fine fescues. Fungicides labeled to control red thread and pink patch on home lawns include Cleary's 3336 (thiophanate methyl), Bayleton (triadimefon), and those containing mancozeb as the active ingredient.


Step-by-step photos of lawn renovation

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