Does your lawn have what appears to be dying patches with pink or reddish fibers in them? This may be the telltale sign of red thread. Red thread is a turfgrass disease most commonly caused by low levels of nitrogen in the soil or environmental stress.
Cool-season grasses tend to be the most susceptible to red thread. Common varieties include red fescue, ryegrass, Kentucky bluegrass, and bentgrass. Warm season turf grasses are more resistant to red thread than cool season grasses. Your local Cooperative Extension Service can recommend the best red thread resistant varieties for your area.
Does Red Thread Kill Grass?
While affected areas of grass appear to be dead, red thread doesn't kill the grass. The fungus that infects the turf lives in the thatch and soil and can be spread by dead infected plant material and by mowing and other mechanical maintenance. The pink growths that appear in the grass do not infect the crown or the roots of the plant, so the grass is not killed by the fungus.
Red thread can occur in many different climates but is more common in areas with high rainfall or high humidity in late spring to summer. The primary conditions favoring red thread are:
- Low levels of nitrogen or inadequate overall fertilization
- Temperatures between 68 and 75 degrees Fahrenheit
- High humidity
- Low light levels
- Excessive travel over the grass
Red thread is a growth of the fungus Laetisaria fuciformis. It appears as red thread-like branches, sometimes compared to antlers, called sclerotia. The grass is usually tan or light brown beneath the red thread growths.
Red thread is commonly confused with a disease called pink patch. Pink patch, caused by Limonomyces roseipellis, is a different disease but closely resembles red thread due to similarities in symptoms, disease cycle, epidemiology, host range, and appearance.
Why Your Lawn May Be Affected
Almost any lawn is susceptible to the red thread turf fungus. However, it is not uncommon for some lawns to have more issues than neighboring properties, due to different soil conditions, maintenance, and water patterns.
The cause of red thread and other turf diseases can be understood by looking at three factors, all of which make up a disease "triangle": the susceptible host, the pathogen or disease itself, and an environment favorable to disease growth.
The hosts are grass plants that are lacking in nitrogen and are experiencing slower growth than in prior months. The pathogen is present in the thatch layer of a lawn and is impossible to completely remove. When the plant is weak, and the temperature and relative humidity are favorable for fungal growth, red thread will appear and continue to grow.
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 the fungus stops growing. Since it’s not possible to remove the pathogen or control the weather, the most effective way to manage red thread is to address the susceptible host plant and strengthen it with fertilizer.
The basic treatment for red thread is to fertilize the lawn with the proper amount of nitrogen as part of an ongoing feeding program. Nitrogen applied to the lawn in the fall will nourish the re-emerging turf in the spring, but take care to not overstimulate growth late in the season. It may take two years or more of careful feeding to prevent red thread from coming back in the spring.
An additional control method is to avoid prolonged periods of grass wetness. Irrigation should be done between midnight and 6 AM. Apply a sufficient amount of water to wet the entire root zone and do not water again until the turf first starts to show signs of drought stress.
Prune or remove trees or shrubs to increase sunlight and air movement Bag clippings from affected areas when the disease is active and wash mowing equipment between uses to reduce spread of the disease.
Treating red thread with chemicals is generally not necessary and not recommended for residential lawns. The application of a fungicide should be a last resort for extreme infestations. Consult a lawn-care professional or your Cooperative Extension Service for recommendations on the proper fungicide to use in your area.
Red Thread. Wisconsin Horticulture Society
Cagaš, Bohumír et al. Field Resistance Of Festuca Rubra Varieties To Red Thread (Laetisaria Fuciformis). Sustainable Use Of Genetic Diversity In Forage And Turf Breeding, 2010, pp. 289-293. Springer Netherlands, doi:10.1007/978-90-481-8706-5_40