The Purdue Plant and Pest Diagnostic Laboratory

What's Hot at the P&PDL for
May 28, 2010

Red Thread on Turf

By Gail Ruhl, Senior Plant Disease Diagnostician, Purdue University

Red thread is caused by a fungus (Laetisaria fuciformis) that attacks the grass blades and leaf sheaths of many commonly cultivated turfgrasses including Kentucky bluegrass, perennial ryegrass, and tall fescue. Red
thread gets its name from the red fungal structures that protrude through the tips of infected grass blades Red thread symptoms create brown patches in the lawn, however crowns and roots are not infected, so plants are not killed and turf eventually will recover.

The disease usually occurs from late May through September, when temperatures are between 65-75° F, and especially when evenings are cool and moist. Red thread development is most common where turfgrass nutrition is poor and there are other factors that promote slow growing turf. Thus, fertility of the soil is most important: proper and timely fertilization will reduce the incidence of this fungal disease. Apply 1/2 to 1 pound of nitrogen per 1,000 square feet of turf and maintain good fertility throughout the growing season.

Other cultural practices that will help to prevent disease include watering infrequently but deeply, moistening the soil to a depth of 4-5 inches or more at each irrigation. Mow often so that no more than 1/3 of the leaf blade is removed at each clipping.

Turf Grass Disease Profile: Red Thread

Click image to enlarge

Red thread

Closeup of red thread

Red thread in lawn

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service