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Red Thread Guide

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How to Identify Red Thread Lawn Disease

What Is Red Thread?

Red Thread (Laetisaria fuciformis) is a fungal disease that affects turf grasses, causing visible discoloration and unsightly growth. While it may make the lawn look unhealthy, it is typically not fatal to the grass plants themselves. The disease results in thread-like growths on the grass, but it does not affect the roots or crowns of the grass.

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Appearance

The thread-like growths seen in Red Thread-infected grasses are called sclerotia. These threads are typically red or pink, which gives the disease its name. The condition is usually noticeable to the naked eye, though other lawn diseases like dollar spot, pink patch, and pink snow mold may resemble Red Thread. To confirm Red Thread, look closely for the distinctive red or pink threads (sclerotia) or the small, pink, cotton-like masses (mycelia) that may appear at the tips of leaves.

Effects of Red Thread Fungus Disease

When Red Thread infects a grass plant, blighted spots can develop on the grass blades in as little as two days. These spots will appear on the leaves, stems, and leaf sheaths but do not affect the roots or crown, and may not always lead to plant death.

During drier periods of the growing season, infected grass blades may fade in color or die, often appearing in random patches or forming circular areas on the lawn.

In more humid climates, turf blade death is less common, and the infected plants will produce the signature red or pink threads or cottony mycelia at the tips of the grass blades. These visible signs are the clearest indication that Red Thread is present.

Check our next page on How to Treat Red Thread for DIY treatment tips.
Also, read our Red Thread Inspection Guide to learn more about how to identify this disease on your lawn.

How to Find Red Thread Lawn Disease

Recognizing the Conditions & Symptoms

By learning how to identify the early signs of Red Thread lawn disease, you can take action to address it promptly and restore your lawn. Once you spot Red Thread on your property, this guide will help you locate where it may be spreading, control its growth, and prevent it from returning in the future.

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Step1 Where Does Red Thread Occur?

Red Thread disease can affect various grassy areas, including lawns, sports fields, parks, and golf course roughs.

This disease most commonly affects cool-season grasses, such as fine fescue, Kentucky bluegrass, and perennial ryegrass, especially when these lawns do not have adequate nitrogen. Red Thread is typically seen in the northern U.S., where these turf varieties are more popular due to the cooler climate.

Step2 When Does Red Thread Disease Happen?

Keep an eye out for Red Thread’s distinctive symptoms during the following conditions:

  • Late spring to summer (usually March to June)
  • Fall (September to December)
  • Temperatures between 40°F and 70°F
  • Humid weather conditions

Look for red or pink tendrils growing from grass blades and spots on the grass leaves, especially during rainy or wet seasons in your region.

Step3 What Are the Symptoms of Red Thread to Watch For?

Watch for the following signs of Red Thread infection in your lawn:

  • Small, circular patches of discolored turf, which may appear faded tan, pink, or red, depending on the disease stage. These patches can sometimes merge to form larger areas.
  • Grass blades may show discolored spots, leading to dried, faded grass and eventually plant death.
  • Red thread-like growths may be visible on the tops of grass shoots or stems, particularly in wetter conditions or when humidity is high. These red or pink fibers resemble small threads or antler-like extensions.
  • Fluffy, cotton-like growths (mycelia) can also form on infected grass blades, often at the tips, appearing as pink cotton blobs.

These combined symptoms can lead to a reduction in turf density and a less attractive appearance for your lawn.

For information on how to treat Red Thread fungal disease, visit our Red Thread Treatment Guide.

How to Treat Red Thread Lawn Disease

Apply the Right Product at the Right Time

Red Thread is a lawn disease that can be mostly cosmetic, though it can still cause damage to the turf if not treated. This fungal disease can be controlled with a combination of soil amendments and chemical treatments. Below are our recommended steps to treat Red Thread and get your lawn back in shape.

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Step1 Check Your Soil’s Nitrogen Levels and Fertilize to Combat Red Thread

In many cases, Red Thread is directly linked to a nitrogen deficiency in the soil. To determine whether this is the issue, use a home soil test kit to evaluate your lawn’s nutrient levels. Your local extension service can help interpret the results and recommend missing macronutrients.

If nitrogen levels are low, select a fertilizer with higher nitrogen content that is appropriate for your lawn type and region. Proper fertilization strengthens your lawn and helps it resist Red Thread and other fungal diseases.

To determine the right fertilization schedule, follow recommendations based on your lawn's needs. A common guideline is applying ½ to 1 pound of nitrogen per 1,000 square feet, but always follow specific recommendations for your lawn’s health.

For cool-season lawns, be cautious not to over-fertilize with nitrogen during warm weather, as this could encourage further fungal growth like Brown Patch. Use a lower-nitrogen fertilizer during summer heat or organic amendments like iron.

Step2 Apply a Fungicide to Control Persistent Red Thread Growth

Fertilization alone will control Red Thread in most residential lawns, but for larger infestations, or on high-value turf (like golf courses), applying a chemical fungicide can help minimize or control the disease. Fungicides work best when applied during periods of wet weather when fungal growth is most active.

Fungicides with QoI (FRAC Group 11) or DMI (FRAC Group 3) ingredients, such as azoxystrobin or propiconazole, are effective against Red Thread. To avoid resistance, rotate between fungicides from different FRAC Groups.

For the best results, apply fungicide when you can visibly see the red or pink tendrils (sclerotia) on your turf. Ensure you follow all labeled instructions regarding timing, rate of application, and rotation with other products to prevent resistance.

Products we recommend for Step 2

For more information about Red Thread disease prevention, check out the next page in our guide

How to Prevent Red Thread Lawn Disease

Prevent Red Thread Disease with Proper Lawn Care

Red Thread disease can leave your lawn with dry, discolored grass blades and the distinctive appearance of tiny pink or red threads growing from the turf. The best approach to prevent a Red Thread infestation is through consistent lawn care and ensuring your turf receives the necessary nutrients to ward off the fungus.

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Step1 Maintain a Healthy Lawn

How to Water Your Lawn
Our Lawn Care Calendars offer helpful schedules for these essential lawn care practices.

  • Follow proper watering methods to avoid long periods of grass leaf wetness.
  • Regularly mow the lawn, ensuring you never remove more than one-third of the grass height during each session.
  • De-thatch the lawn yearly to prevent excessive thatch, which can shelter Red Thread.
  • Aerate the turf annually to reduce soil compaction and enhance drainage.
  • Provide adequate space between new plantings to allow sunlight to reach the grass.

Step2 Fertilize Your Lawn to Maintain Nitrogen Levels

How to Apply Granular Lawn Fertilizer
Lawns deficient in nitrogen are particularly susceptible to Red Thread disease. By following a fertilization plan based on your soil test results, you can ensure your turf gets the right nutrients to grow strong and fight off fungal diseases.

Start by collecting soil samples as instructed by your home soil test kit. Your local extension service can help you interpret the results and guide you in selecting the best fertilizer for your lawn.

Make sure to choose a fertilizer suitable for your turf and climate. Begin with a preventive fertilization schedule based on the recommendations for your specific lawn needs.

Be mindful that over-fertilizing can lead to additional problems, including other fungal diseases, especially in warmer weather. Excessive nitrogen during hotter months can make your lawn more vulnerable to issues like Brown Patch fungus.

Not sure if you've spotted Red Thread on your lawn?
Check out our Red Thread Identification Guide to help you identify the disease before taking action.

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