What To Do If You Spot Round Brown Spots In Your Lawn And Grass

With lawn care season in full swing, you might dutifully mow the grass and ensure your lawn is getting the water and nutrients it needs to grow healthy. Aside from lush, green grass and no bare spots, other common signs of a healthy lawn include a lack of weeds, just the right amount of thatch, and the resilience to withstand kids and pets playing in the yard. Seeing brown spots, on the other hand, can be disheartening. Seeing numerous, round brown spots can indicate lawn diseases, especially in certain types of grasses. After ruling out other potential causes of brown spots, such as pet urine or a lack of water of fertilizer, it may be time to investigate whether your lawn has been afflicted with turf necrotic ring spot (Ophiosphaerella korrae) so you can take steps to contain the damage.

Necrotic ring spot (NRS) is a fungal disease known for creating patches of doughnut-like, ring-shaped brown spots in home lawns. It primarily affects cool-season Kentucky bluegrass lawns within the first few years of installation, but more established turf and other types of cool-season grasses sometimes fall victim to this unsightly disease. These include annual and rough bluegrasses, as well as fine fescue. NRS develops and spreads within grass roots before moving to the crowns, and is usually most noticeable in the spring and fall, when the cool, wet weather allows the fungus to thrive. Even worse, grass that's infected with NRS takes months or years to recover. The rings turn increasingly yellow each year. Sometimes, affected spots can die and create visible depressions in your yard and be taken over by weeds.

There are tall-tale signs of NRS everyone with cool-season turfgrass ought to look out for. This fungal disease often first presents during cool wet weather in the spring, first as patches that are lighter green than the rest of the surrounding turf. These circular areas can then grow in size and eventually turn red or brown, particularly when weather conditions are hot and dry, and grassroots can no longer take in water due to extensive damage. Spots may start in sizes of ½ to 1 foot in diameter before getting as large as 3 feet! These also persist into the fall season.

When inspected more closely, you might see other characteristic signs of NRS. While blades may look dark yellow or brown, you may notice individual sheaths turn dark brown (or even black) in color. In the fall, you might see red blades of grass in the mix. Any grass that comes up with a simple tug test is also concerning, especially if you see the roots are visibly rotted. Wilted grass is another red flag for NRS, particularly during the summer months.

All of these signs can point to NRS in your lawn. However, the only way to obtain definite confirmation of this fungal disease is by testing the afflicted areas. This is typically done by a university extension office, which can diagnose samples of turf (including roots) you collect in a clean plastic bag (keep it at about room temperature to ensure the fungus stays alive). Once you've determined NRS has infected your lawn, it's time to take steps to contain the spread.

There are two primary approaches to treating NRS in turfgrass. Commercial fungicides are perhaps the easiest method to try to treat NRS, but know that results are mixed. If you do go the chemical route, be sure to follow all product instructions and select one that is specifically labeled for NRS treatment. Azoxystrobin and thiophanate methyl-based fungicides tend to work best to treat this type of infection, especially when the grass is watered beforehand. Some homeowners with Kentucky bluegrass also sometimes choose to apply fungicides in spring as preventive measures against NRS, but the right ingredients are key to success. In these cases, choose products with propiconazole, fenarimol, or myclobutanil.

A more effective means of control is to physically remove NRS spots directly. Depending on the extent of the brown spots, this process may be done by hand or with the help of a shovel. Once all affected grassroots are removed, you may need to reseed any spots of bare lawn. To prevent further spread, make sure you thoroughly clean your garden tools or lawn equipment that's made direct contact with NRS-infected grass. 

Anyone with Kentucky bluegrass lawns can help keep their grass healthy by practicing steps that thwart the growth of NRS. Preventative measures can involve watering your lawn deeply but infrequently during the wet season. Increase watering sessions during hot, dry weather to prevent NRS spread. Applying slow-release fertilizers, especially a nitrogen-rich blend, can also work to suppress NRS throughout the season by ensuring your grass gets adequate nutrients to fight against infection. The previously mentioned preventative fungicides also require adequate nitrogen in the soil to work. Finally, make sure your grass is aerated annually to support healthy roots and reduce soil compaction.