NRS (Necrotic Ring Spot) Fungus: The Ultimate Guide

NRS (Necrotic Ring Spot) Fungus: The Ultimate Guide

Owning a home with a beautiful backyard is a dream come true for many. However, the discovery of brown rings in your turfgrass can quickly turn that dream into a nightmare. If you suspect that your lawn is affected by necrotic ring spot (NRS), it’s crucial to take immediate action. In this comprehensive guide, we will explore what a necrotic ring spot is, its symptoms, and, most importantly, how to get rid of it effectively. By following these steps, you can restore the health and beauty of your lawn.

Understanding Necrotic Ring Spot

Necrotic ring spot is a lawn disease caused by the fungus Ophiosphaerella korrae. It primarily affects cool-season grasses and is classified as one of the patch diseases. Unlike other patch diseases, NRS damages the crown and roots of grass blades, leading to root rot and the formation of tan rings with healthy grass in the middle. The disease typically develops in the late spring or fall when the soil temperature is between 65 to 70 degrees Fahrenheit. It is commonly found in sod lawns that are two to three years old.

Identifying the Symptoms

To effectively combat necrotic ring spots, it is crucial to be able to identify its symptoms. Here are some important things to look for:

1. Light Green Patches

The first sign of necrotic ring spots may appear as light green patches on your lawn. These patches gradually develop into bronze rings with healthy, green grass in the center, creating a distinctive frog-eye appearance.

2. Straw-Colored Rings

As the disease progresses, the bronze grass weakens and turns straw-colored. In some cases, these rings may appear sunken, further indicating the presence of necrotic ring spots.

3. Varying Sizes

Necrotic ring spot rings can range in size from a few inches to several feet in diameter. It’s important to note that these rings tend to grow larger each year, posing a greater threat to your lawn’s overall health.

4. Root Rot

Upon closer inspection, you may notice that the roots, crowns, and lower stems of the affected grass appear black or brown due to root rot caused by the necrotic ring spot fungus.

Accurate Diagnosis

While the symptoms mentioned above can strongly indicate necrotic ring spots, it is essential to obtain an accurate diagnosis to rule out other patch diseases, pest problems, or unhealthy lawn practices. To achieve this, consider sending a sample of the diseased grass to a turfgrass diagnostics laboratory at your local university or cooperative extension. Their expertise will ensure an accurate diagnosis and guide you toward the most effective treatment options.

Effective Treatment Methods

Now that we have a clear understanding of necrotic ring spot and its symptoms, let’s explore the most effective ways to combat this lawn disease. While fungicides are available for control, their effectiveness against NRS can be inconsistent. Therefore, it is advisable to combine fungicide treatment with good lawn maintenance practices to maximize your chances of success.

1. Water Lightly

One of the primary reasons for the dying grass in necrotic ring spot rings is the inability of rotting roots to uptake nutrients and water. Light watering can help repair the affected areas, particularly during the summer months. It is recommended to irrigate the ring spots daily with 0.1 to 0.2 inches of water between noon and 4 p.m. During extended periods of drought, you can double this rate. However, it’s important to note that this watering schedule should only be applied to the affected areas and not the entire lawn. Stick to your regular watering schedule for the rest of your lawn, preferably before 10 a.m., ideally before 8 a.m.

2. Raise the Mowing Height

Maintaining the proper mowing height is crucial for promoting a healthy root system in your turfgrass. Avoid mowing the grass too low, as this encourages shallow and weak roots. Instead, raise the mower blades to the highest recommended mowing height for your grass type. This simple adjustment will help promote a healthier root system and overall lawn health.

3. Aerate the Soil

Aeration is an effective technique for relieving soil compaction and improving drainage, which is crucial for maintaining healthy roots. Core aeration, using a specialized tool called a core aerator, helps break up compacted soil and allows roots to grow deeply. Improved access to water, oxygen, and nutrients promotes healthier grassroots.

4. Apply Balanced Fertilizer

A well-nourished lawn with a strong root system is better equipped to fight off diseases like necrotic ring spot. Applying a balanced fertilizer regime using slow-release fertilizers containing nitrogen, phosphorus, and potassium can help promote healthy grass growth and recovery. It is essential to monitor the soil’s nutrient levels and adjust the fertilizer application accordingly.

5. Apply Sulfur Amendments

According to the Colorado State University Extension, applying sulfur amendments can impede the NRS pathogen by acidifying the soil. It is recommended to apply sulfur in split applications, totaling 1 to 1.5 lbs. of elemental sulfur per 1,000 square feet per year. Water the sulfur into the soil to avoid turfgrass damage. Regular soil tests should be performed to monitor the soil pH and sulfur application should be discontinued if the pH drops below 6.0.

6. Overseed with Resistant Varieties

Overseeding the affected areas with resistant turfgrass varieties can help mask the presence of necrotic ring spots and aid in the repair process. However, it’s important to note that the new grass type may differ in shade of green, potentially impacting the uniformity of your yard. Kentucky bluegrass is the grass type most vulnerable to NRS, while perennial ryegrass and tall fescue are immune to the disease and can be considered for overseeding.

7. Consider Fungicide Applications

While the effectiveness of fungicides against necrotic ring spots can be inconsistent, they may offer a solution when other lawn care measures have been exhausted. It’s important to note that not all fungicides can be applied by homeowners and may require professional assistance. Thiophanate-methyl and azoxystrobin fungicides are commonly used for curative NRS treatment, while fenarimol, myclobutanil, and propiconazole are best applied preventively.

8. Prevention is Key

Preventing necrotic ring spots and other lawn diseases is always better than trying to treat them. Practicing good lawn care habits can give your lawn a strong defense against diseases like NRS. Here are some essential preventive measures:

  • Clean your lawn regularly to remove leaves and organic debris that can block the sun and attract pests.
  • Mow your grass properly, avoiding the removal of more than one-third of the grass blade’s length during a single mow.
  • Choose disease-resistant grass varieties suitable for your lawn and climate.
  • Leave grass clippings on the lawn to decompose, as they provide nutrients to the soil.
  • Practice pest control to prevent lawn damage from grubs and other pests.
  • Water your lawn less often but deeply to encourage a deep, healthy root system.
  • Avoid overwatering, as it creates an environment conducive to lawn diseases.
  • Consider investing in a sprinkler system for efficient and precise watering.
  • Conduct regular soil tests to monitor soil health and make necessary amendments.
  • Fertilize your grass appropriately to provide essential nutrients.
  • Spread compost on your lawn to provide organic nutrition.
  • Aerate the soil to alleviate compaction and improve root growth.
  • Remove excessive thatch, as it can harbor pests and diseases.
  • Overseed to promote a thick, dense lawn that outcompetes weeds.
  • Remove existing weeds manually or with the help of a post-emergent herbicide.
  • Apply pre-emergent herbicides to prevent weed growth in your yard.

Grass Types Susceptible to Necrotic Ring Spot

Necrotic ring spot primarily affects cool-season grasses such as Kentucky bluegrass, rough bluegrass, annual bluegrass, and fine fescue. Among these grass types, Kentucky bluegrass is the most vulnerable to NRS. It’s important to note that some warm-season grasses, like bermudagrass, can also be infected by the disease.

Other Grass Diseases to Watch Out For

While necrotic ring spot is a significant concern for lawn owners, it is not the only disease that can harm your turfgrass. Here are some other common turfgrass diseases to be aware of:

  • Anthracnose
  • Brown patch
  • Dollar spot
  • Fairy ring
  • Gray snow mold
  • Bentgrass leaf spot and melting-out
  • Pink snow mold
  • Powdery mildew
  • Red thread
  • Rust
  • Summer patch


Q: What is the difference between a necrotic ring spot and a fairy ring spot?

A: Both necrotic ring spots and fairy ring spots appear as brown, dried circles on your lawn. However, fairy rings are generally larger and sometimes very green. Necrotic ring spots are usually tan or brown rings of dead-looking grass, typically 12 inches or less in diameter.

Q: What should I do if I can’t identify my lawn disease?

A: If you’re having difficulty identifying the specific lawn disease affecting your grass, it is recommended that you contact a local diagnostic lab or turfgrass pathology lab. They have the expertise to provide an accurate diagnosis and guide you toward appropriate treatment options.

Q: Will the necrotic ring spot go away on its own?

A: No, the necrotic ring spot will not go away on its own. Without treatment, the disease will continue to spread and infect more of your lawn. Timely treatment is crucial for eliminating the disease.

Q: Should I hire a professional for lawn care?

A: While effective lawn care maintenance is essential for treating and preventing diseases like necrotic ring spots, it can be time-consuming and labor-intensive. If you find yourself lacking the time or expertise, consider hiring a professional lawn care service. Companies like ECO Lawn Utah can connect you with trusted professionals who can ensure your lawn remains healthy and vibrant.


Necrotic ring spots can pose a significant threat to the health and beauty of your lawn. However, armed with the knowledge and techniques outlined in this guide, you can effectively combat the disease and restore your turfgrass to its full glory. Remember to diagnose accurately, implement proper lawn care practices, and consider professional assistance when necessary. By following these steps and practicing preventive measures, you can enjoy a lush, disease-free lawn for years to come.

Get in touch with EcoLawn today for help with your lawn. Our team focuses on making your lawn look great while also being eco-friendly. You can visit ECO Lawn Utah or email us at to set up an appointment and start improving your lawn in an environmentally friendly way.