Enjoying your backyard is one of the best parts of home ownership, so finding brown rings in your turfgrass is a pain. To get rid of those patches, you need to find out what they are. But they could be anything from drought stress to necrotic ring spot. If you think it might be the latter, you need to act fast. Let’s discover what necrotic ring spot is and how to get rid of it.
What is necrotic ring spot?
Necrotic ring spot (NRS) develops from the lawn fungus Ophiosphaerella korrae and affects cool-season grasses. NRS is included in a group of lawn diseases called “patch diseases,” although they’re not actually scientifically related. NRS damages the crown and roots of your grass blades, causing root rot and rings of tan turf with healthy grass in the middle.
Like many patch diseases, NRS typically develops in the late spring or fall when the soil temperature hovers between 65 to 70 degrees Ferinheight. It’s commonly found in sod lawns two to three years after development. Unfortunately, it can be difficult to diagnose as its symptoms are similar to other patch diseases, pest problems, or unhealthy lawn practices.
Pro tip: For an accurate diagnosis, send a sample of the diseased grass to a turfgrass diagnostics laboratory at your local university or cooperative extension.
What are the symptoms of necrotic ring spot?
If you suspect your yard has NRS, here are the symptoms to look out for:
- Light green patches: Symptoms may first appear as light green patches. These patches eventually develop into bronze rings with healthy, green grass in the middle, creating a frog-eye appearance.
- Straw-colored rings: The bronze grass eventually weakens and turns straw-colored. In some cases, these rings may appear sunken.
- Varying size: Rings can range between a few inches to several feet in diameter, growing larger each year.
- Root rot: Roots, crowns, and lower stems appear black or brown from rot.
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.
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. 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 your 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 and can cause your grass to go dormant or die.
Aerate the soil
Roots struggle to remain healthy in compacted soil with poor drainage, 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 grassroots will also have better access to water, oxygen, and nutrients.
Pro tip: While aeration can spread NRS, the benefits of this treatment usually outweigh the risks.
Apply balanced fertilizer
Applying more than four pounds of nitrogen fertilizer per 1,000 square feet per year may intensify NRS. Combat the patch disease 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
To help mask the NRS disease and repair affected areas, overseed patches with resistant turfgrass varieties. However, 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 label instructions for application, storage, and disposal.
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.
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:
- Clean your lawn: Remove leaves and organic debris from your yard. They block the sun, attract pests, and increase the risk of disease.
- Mow properly: 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 disease-resistant grass: Make sure the disease-resistant grass type you plant is suitable for your lawn and climate, or it will struggle.
- Leave grass clippings: Instead of bagging the grass clippings, leave them on the lawn to decompose. They become grass-clipping mulch and add nutrients to the soil.
- Practice pest control: Control grubs and other summer lawn pests.
- Irrigate: Watering less often and for long periods encourages a deep, healthy root system. The best time to water the lawn is before 10 a.m.
- Don’t overwater: Overwatering your grass creates an environment that many lawn diseases love, including NRS.
- Invest in a sprinkler system: A sprinkler system allows you to set it and forget it, saving you time, money, and stress.
- Test your soil: A soil test report reveals the makeup of your soil and what amendments will improve soil health.
- Fertilize your grass: Your grass needs nutrients to grow healthy and strong. Fertilizer basics tell us that most established lawns only need one fertilizer application a year.
- Spread compost: Compost gives your yard an organic nutritional boost.
- Aerate: Soil aeration is key because compacted soil prevents water, oxygen, and nutrients from accessing the grassroots and prevents deep root growth.
- Remove thatch: Thatch is a layer of roots that’s dead but not yet decomposed. It settles between the turfgrass and the soil surface. While a little thatch is good, more than ½-inch thick can harbor pests and diseases.
- Overseed: Overseeding encourages a thick, dense lawn that outcompetes weeds.
- Remove weeds: Overgrown weeds compete with your grass for water, nutrients, sunshine, and space. 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.
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 can also infect some warm-season grasses, like bermudagrass.
What other grass diseases can infect my lawn?
Scot Nelson | Flickr | Public domain
Necrotic ring spot isn’t the only disease that can harm your lawn. Other turfgrass diseases include:
- 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
FAQ about necrotic ring spot
Necrotic ring spot vs. fairy ring spot
Both necrotic ring spot and fairy ring spot appear as brown, dried circles on your lawn, but fairy rings are bigger and sometimes very green.
Necrotic ring spots are usually about 12 inches or less in diameter and are always tan/brown rings of dead-looking grass.
Fairy ring spots are 3 to 20 feet in diameter. Sometimes, they’ll appear as rings of dead grass, but oftentimes, they’ll develop abnormally as green and dense grass. It’s not uncommon for mushrooms to grow around the perimeter.
What if I can’t identify my lawn disease?
Many lawn diseases look similar, so it can be challenging to identify which lawn disease beast you’re dealing with. Unfortunately, if you guess wrong, your treatment attempt can be in vain.
If you’re having trouble figuring out which lawn disease is attacking your lawn, contact a local diagnostic lab or turfgrass pathology lab. They can send you an accurate diagnosis of your infected turf.
Will necrotic ring spot go away on its own?
No, necrotic ring spot will not go away on its own. Like most lawn diseases, if left untreated necrotic ring spot will continue to grow and infect more of your lawn. Treatment is the key to eliminating the disease.
Should I hire a professional?
If you have a lawn disease, lawn care maintenance is critical to healing your lawn. But even if you don’t have lawn problems, lawn care takes a lot of time and hard work. If you don’t have the time to do yard work, you’re not alone. Homeowners nationwide are getting help carrying the lawn care load.
But finding an efficient, affordable, and trustworthy professional can be a monumental task all on its own. That’s where Lawn Love can help. We search high and low to find the perfect local lawn care professional. They’ll have your yard immaculate and luscious in no time without costing an arm and a leg.
Main photo credit: Ninjatacoshell | Wikimedia Commons | CC BY-SA 3.0
