Red Thread Grass

Treatment and Prevention

Red thread grass
Kris Lord / Flickr / CC By 2.0

Do you have some dying patches on my lawn with reddish fibers in them? The presence of red or pink webbing or thread is the telltale sign of red thread. Red thread is a turfgrass disease most likely brought on by low levels of nitrogen in the soil. This disease typically appears between late April and mid-June, but can possibly be found during most of the growing season. It most often appears in the months of May and June when nighttime temperatures are hanging around 70° F and lawns have aggressively grown, using up most of the nitrogen in the soil.

Conditions favoring red thread:

  • Low levels of nitrogen
  • Temperatures between 68˚ and 75˚
  • High humidity

Cool season grasses such as red fescue, ryegrass, Kentucky bluegrass, and bentgrass are most susceptible. Some varieties have red thread-resistant qualities including '​Bilart' and 'Claudia' fine fescues; 'Chateau' Kentucky bluegrass; and 'Pennant' perennial ryegrass.

What Red Thread Looks Like

The educators at Purdue University say red thread takes its name from the antler-like structures (sclerotia) produced by a fungus (Laetisaria fuciformis) on the tips of infected leaf blades. The red or pink sclerotia are visible without magnification and are useful for identifying the disease in the field. From a distance, red thread symptoms appear as circular patches of tan or pink turf about 4 to 8 inches in diameter. The pink color is caused by the sclerotia and/or flocks of pink mycelium on leaf blades.

Other diseases, including dollar spot, pink snow mold, and especially pink patch, have field patterns and symptoms that resemble red thread and are active during similar environmental conditions. However, after close inspection, red thread is easily distinguished from other diseases by the presence of the sclerotia.

Treatment

Almost any lawn is susceptible to this turf fungus. However, it isn’t uncommon for some lawns to have more issues than neighboring properties. Property owners often wonder what can be done to get rid of red thread on lawns when it shows up each year. The remedy is to disrupt the disease triangle so that this fungus stops growing.The disease triangle is used to illustrate how fungi grow on plants, in this particular case, your lawn. The susceptible hosts are grass plants that are lacking in nitrogen and have started to not grow as aggressively as they have in the months prior. The pathogen is present in the thatch layer of a lawn and impossible to completely remove. When the plant is weak, and the temperature and relative humidity is favorable, red thread will begin and continue to grow.

Since it’s not possible to remove the pathogen nor control the weather, the most effective way to manage red thread is to address the susceptible host plant. Fertilizing lawns in late spring and early summer will help to provide nitrogen. As that nitrogen gets watered in, most lawns will grow-out this specific turf disease problem. That being said, there are instances where red thread can become a chronic problem or advance past normal levels and a fungicide treatment may be required.

This isn’t typical, but it can happen.