Spotting Red Thread: Your Guide to Identifying and Treating Lawn Fungus

If you’re a lawn owner, you may have heard of the term “red thread” before. This lawn disease is a common problem for many homeowners, causing patches of grass to turn brown and die off. In this article, we’ll discuss what red thread is, whether it can kill your lawn, and how to treat and prevent it.

What is Red Thread?

Red thread is a fungal disease caused by the fungus Laetisaria fuciformis. The fungus feeds on the nutrients in the grass and weakens it killing the leaf but not the plant, this also makes it more susceptible to other diseases and environmental stressors. It can spread quickly, especially in areas where the grass is damp and there is poor air circulation.

When the fungus is active it is easy to spot by paying close attention to the red threads but when it has been and gone it is a little harder to spot as the lawn looks like it is just going brown. The patterning can often help in this case.

It is called “red thread” because it appears as small patches of red “cotton” thread-like veins on your lawn. It can also be accompanied by a cotton wool-like growth. These patches are usually random in shape and can range in size from a few inches to several feet in diameter. Red thread is most commonly found in cool and humid climates, and it thrives in damp and shaded areas.

What Causes Red Thread in Lawns?

Red thread is caused by a combination of factors, including moisture, humidity, and poor soil nutrition. It thrives in damp and shaded areas and is more prevalent in the spring and autumn when the temperatures are cooler.

Like any fungus, it thrives when conditions are right. It is the most common of all lawn fungi and it tends to take hold on stressed plants so if you are overfeeding and creating lush growth, or the lawn is drought stressed but being watered you are likely to get red thread in your lawn.

Another factor that can contribute to red thread is poor soil drainage. If your lawn is in a low-lying area or has heavy clay soil, it may not drain well, leading to the build up of moisture and the development of fungal diseases.

Will Red Thread Kill My Lawn?

While red thread can damage your lawn and make it look unsightly, it’s not likely to kill your grass. The fungus that causes red thread feeds on the surface of the grass blades, but it doesn’t typically invade the roots or crowns. However, severe cases of red thread can weaken your lawn, making it more susceptible to other diseases and environmental stresses.

How to Treat Red Thread in Lawns?

The good news is that red thread is a relatively easy disease to treat, and it rarely causes permanent damage to your lawn. Effectively you need to improve the plant’s growing conditions so that it is at optimum health. This makes it more resistant to the disease. Here are some steps you can take to treat red thread in your lawn:

  1. Improve soil nutrition: Red thread thrives in lawns with poor soil nutrition. To improve soil nutrition, consider adding a slow-release fertiliser that is high in potassium and has balanced nitrogen. Nitrogen helps the plant replace the affected leaves. You can also include a small amount of iron which increases the strength of the cell walls in the plants which also helps resist attack.
  2. Aerate your lawn: a healthy rootzone means a healthy plant.
  3. Increase air circulation: Red thread loves damp and shaded areas. To increase air circulation in your lawn, trim your trees and shrubs to allow more sunlight to reach your lawn.
  4. Reduce moisture: Red thread needs moisture to thrive. To reduce moisture in your lawn, consider watering your lawn in the morning to allow it to dry out during the day.
  5. Apply fungicide: If red thread persists, consider applying a fungicide to your lawn. There are many fungicides available on the market that are effective against red thread.


Red thread may be a common problem for lawn owners, but it’s not a death sentence for your grass. By following the steps outlined in this article, you can effectively treat and prevent red thread in your lawn, keeping your grass healthy and green. Remember to practice good lawn care habits, such as proper watering and fertilisation, to keep your lawn strong and resilient against diseases.

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