What is Necrotic Ring Spot and How to Get Rid of It

Donut-shaped rings are appearing in your turfgrass, but are you confident it’s necrotic ring spot and not a different lawn disease with similar symptoms? We’ll show you the best way to identify necrotic ring spot and how to get rid of it. 

This turfgrass disease attacks your lawn’s roots, making for a slow recovery. But with the right management strategies in place, you can revive your lawn’s health and prevent future fungal infections. 

How to identify necrotic ring spot

Necrotic ring spot (NRS) symptoms can be easily confused for summer patch disease. Both diseases can develop rings of tan turf with healthy grass in the middle and cause root rot. To receive an accurate diagnosis, send a sample of the diseased grass to a turfgrass diagnostics laboratory at your local university or cooperative extension. 

If you suspect your yard has NRS, here are the symptoms to look out for: 

  • Symptoms may first appear as light green patches in the yard. These patches eventually develop into rings of bronze grass with healthy, green grass in the middle, creating a frog-eye appearance. 
  • The bronze grass eventually weakens and turns straw-colored. In some cases, these rings may appear sunken. 
  • The lawn fungus attacks the turfgrass during cool, wet weather in spring and fall. Symptoms become apparent in summer under heat and drought stress. 
  • Rings can range between a few inches to several feet in diameter, growing larger each year. 
  • Roots, crowns, and lower stems appear black or brown from rot. 
  • NRS usually appears in sod lawns two to three years after establishment.

How to get rid of necrotic ring spot

NRS is a turfgrass root disease, and the best way to manage it is to ensure your turfgrass has a strong root system. With a few changes to your lawn care routine, you can help nurse your yard back to health. 

While fungicides are available to control necrotic ring spot, their effectiveness against the disease is often inconsistent, so you want to combine them with good lawn maintenance. 

Ready to restore your lawn’s beauty? Here’s what you can do: 

Water lightly

The rings have dying grass because the rotting roots can’t uptake nutrients and water. Light watering can help repair the affected areas, especially during the summer months. 

Irrigate the ring spots daily with 0.1 to 0.2 inches of water between noon and 4 p.m. You can double this rate during long periods of drought. 

But remember, this watering schedule doesn’t apply to your whole lawn –– just the affected areas. Stick to your regular watering schedule for the rest of your lawn, which should be done before 10 a.m, ideally before 8 a.m. 

Raise the mowing height

Mowing the grass too low encourages a shallow and weak root system. Raising the mower blades to your grass type’s highest recommended mowing height will promote a healthier root system. 

Pro Tip: Never cut off more than one-third of the grass blade’s height during a single mow. Cutting too much grass at once is stressful for your turf. For example, if your grass is 3 inches tall, don’t remove more than 1 inch. 

illustration showing how aeration works and the benefits of aerating soil

Aerate the soil

Roots struggle to remain healthy in compacted soil, making them vulnerable to necrotic ring spot fungus. Aerating your lawn with a core aerator relieves soil compaction and allows the roots to grow deeply. The grass roots also will have more access to water, oxygen, and nutrients. 

While aeration can spread NRS, the benefits of this treatment usually outweigh the risks. 

Apply balanced fertilizer

Applying more than 4 lbs. of nitrogen fertilizer per 1,000 square feet per year may intensify NRS. 

Combat NRS with a balanced fertilizer regime that uses slow-release fertilizers containing nitrogen, phosphorus, and potassium. Your grass will struggle to recover if the soil is nutrient deficient. 

Apply sulfur amendments

According to the Colorado State University Extension, sulfur amendments can impede the NRS pathogen by acidifying the soil. 

The extension recommends applying the sulfur in split applications for a total of 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. Each year, perform a soil test to monitor the soil pH and stop the sulfur application if the pH drops below 6.0. 

Overseed with resistant varieties

Overseeding NRS patches with resistant varieties can help mask the disease and repair affected areas. But some homeowners choose not to overseed because the new grass type can ruin the yard’s uniformity by being a different shade of green. 

The grass type most vulnerable to NRS is Kentucky bluegrass. Kentucky bluegrass varieties with moderate NRS resistance include: 

  • Adelphi
  • Award
  • Classic
  • Eclipse
  • Majestic
  • Midnight
  • Mystic
  • Unique
  • Wabash

Pro Tip: Consider overseeding with perennial ryegrass or tall fescue, which are immune to NRS. 

Apply fungicides

The effectiveness of fungicide against NRS is inconsistent. If NRS perseveres after exhausting all lawn care measures, fungicide applications might offer a solution, but there’s no guarantee. 

Whether you use fungicides as a preventative or curative measure, always read and follow the labeled instructions for application, storage, and disposal. Every fungicide product is different, and instructions will explain the best method and timing for application. 

Thiophanate-methyl and azoxystrobin fungicides may be used for curative NRS treatment. Fenarimol, myclobutanil, and propiconazole are best applied as preventive measures. 

Keep in mind that some fungicides can only be applied by a lawn care professional. Contact a local lawn care company to learn more about your fungicide treatment options. 

Kentucky Bluegrass Lawn

How to prevent necrotic ring spot

The best way to prevent lawn diseases, including NRS, is to practice good lawn care. The healthier your lawn, the less vulnerable it will be to disease. Bad watering habits, poor fertilization, and compacted soil can all encourage fungal disease. 

By practicing the following lawn care treatments, you can give your lawn the health boost it needs to thwart NRS and other lawn diseases: 

  • Remove leaves and other debris from the yard. A thick layer of leaves on the lawn can weaken the grass by preventing photosynthesis. Diseases and pests also overwinter in leaves and dead plant material.  
  • Mow the grass regularly (and correctly). Poor mowing habits can be stressful for your turf. Never remove more than one-third of the grass blade’s length during a single mow, and don’t mow the grass too short. 
  • Plant grass seed that’s disease-resistant and suitable for your lawn. Grass will struggle to grow if it’s not growing in a suitable climate. If you live up North, grow cool-season grass. If you live in the South, grow warm-season grass. If you’re sandwiched between the two, you can plant either grass type
  • Leave behind grass clippings. Instead of bagging the grass clippings, leave them on the lawn to decompose and add nutrients to the soil. 
  • Control grubs and other pests. If pests overrun your lawn, the turf will weaken and become more susceptible to disease. 
  • Perform proper irrigation practices. Watering less often and for long periods encourages a deep, healthy root system. Watering too often and for short periods encourages a weak root system. The best time to water the lawn is before 10 a.m. Avoid watering the grass in the evenings. 
  • Invest in a sprinkler system. Don’t want to wake up at the crack of dawn? Leave your irrigation chores to an automatic sprinkler system
  • Test your soil. You need healthy soil to have a healthy lawn. A soil test reveals what amendments will improve soil health. 
  • Fertilize your grass. Your grass needs nutrients to grow healthy and strong. Most established lawns only need one fertilizer application a year. 
  • Spread compost across the lawn. Compost can give your yard an organic nutritional boost. Spread it as a top dressing or liquid compost tea. 
  • Aerate compacted soil. Compacted soil prevents water, oxygen, and nutrients from accessing the grass roots. It also prevents deep root growth. 
  • Remove thatch that exceeds ½-inch thick. A thin layer of thatch acts as mulch for the lawn, but thick thatch can harbor pests and diseases. 
  • Overseed the lawn. Overseeding encourages a thick, dense lawn that outcompetes weeds. 
  • Remove existing weeds. Weeds compete with your grass for water, nutrients, sunshine, and space. They can eventually crowd out your grass if you don’t control them. You can remove existing weeds manually or with a post-emergent herbicide. 
  • Apply pre-emergent herbicide. Pre-emergent herbicides prevent weeds from growing in the yard. They do not kill existing weeds. 

What grass types are susceptible to necrotic ring spot?

The soil-borne fungus that causes NRS, Ophiosphaerella korrae, damages cool-season grasses, including Kentucky bluegrass, rough bluegrass, annual bluegrass, and fine fescue. 

Kentucky bluegrass is the most vulnerable to NRS. The disease also can infect some warm-season grasses, like bermudagrass. 

What other grass diseases can infect my lawn?

Necrotic ring spot isn’t the only disease that can harm your lawn. Other turfgrass diseases include: 

Leave fungus control to the pros

After a busy work week, do you really want to spend your weekend removing fungus from the lawn? Hire a local lawn care professional to rid your yard of NRS and other lawn diseases. From mowing the lawn to aerating the soil, a lawn care pro keeps the fungus at bay. 

Main photo credit: Ninjatacoshell | Wikimedia Commons | CC BY-SA 3.0

Jane Purnell

Jane Purnell is a freelance writer and actor in New York City. She earned her B.A. from the University of Virginia and enjoys a warm cup of French press coffee.