How to Keep Red Thread Fungus From Taking Over Grass

Does your lawn have what appear to be dying patches with pink or reddish fibers in them? This condition may be the telltale sign of red thread fungus (Laetisaria fuciformis). Red thread fungus is a turfgrass disease most commonly caused by low nitrogen levels in the soil or environmental stress.

Here are several chemical and natural solutions for getting rid of red thread fungus:

• Fertilize the lawn with the proper amount of nitrogen
• Avoid overly wet grass; also, don't let grass dry out
  
• Increase sunlight and air movement
• Bag clippings of infected grass
• Remove excessive thatch
• Reduce traffic on the grass
• Apply fungicide as a last resort
  

Ways to Rid Your Lawn of Red Thread Fungus

Treating red thread fungus with chemicals is unnecessary 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.

Property owners often wonder what can be done to eliminate red thread fungus on lawns when it shows up each year. The remedy is to disrupt the fungus from growing. Since removing the pathogen or controlling the weather is impossible, the most effective way to manage red thread fungus is to address the susceptible host plant and strengthen it with fertilizer.

The basic treatment for red thread fungus 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 not to overstimulate growth late in the season. It may take two years or more of careful feeding to prevent red thread fungus 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 a.m. Apply sufficient water to wet the 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 the spread of the disease.

How to Identify Red Thread Fungus

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 fungus 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.

Does Red Thread Fungus Kill Grass?

While affected grass areas appear dead, red thread fungus 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, mowing, and other mechanical maintenance. The pink growths in the grass do not infect the crown or the plant's roots, so the fungus does not kill the grass.

Ideal Conditions for a Red Thread Fungus Invasion

Red thread fungus can occur in many climates but is more common in areas with high rainfall or humidity in late spring to summer. The primary conditions favoring red thread fungus 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

Why Your Lawn Has Red Thread Fungus

Almost any lawn is susceptible to 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 fungus 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 condition itself, and an environment favorable to disease growth.

The hosts are grass plants lacking nitrogen and experiencing slower growth than in prior months. The pathogen is present in the thatch layer of a lawn and is impossible to remove altogether. When the plant is weak, and the temperature and relative humidity are favorable for fungal growth, red thread fungus will appear and continue to grow.

Although it's a fungus, it does not spread by spores like other fungi; instead, it infects healthy turf via mycelium growth, like fungal branching roots. It can survive unfavorable conditions by remaining dormant in infected grass.

Grasses Susceptible to Red Thread Fungus

Cool-season grasses tend to be the most susceptible to red thread fungus. Common varieties include red fescue, ryegrass, Kentucky bluegrass, and bentgrass. Warm-season turf grasses are more resistant to red thread fungus than cool-season grasses. Your local cooperative extension service can recommend the best red thread-resistant varieties for your area.