It’s been another long hard summer for our lawns. Across the country, drought and extreme temperatures have left our lawns stressed, weak and vulnerable to pests and disease. There’s one disease that’s particularly troublesome during this late summer season, wreaking havoc in Kentucky bluegrass lawns and frustrating homeowners across the country – necrotic ring spot. In fact, this past weekend I received this frantic text message from my sister: “Ever heard of necrotic ring spot? My in-law’s lawn has it. Help!” Necrotic ring spot, the bane of Kentucky bluegrass, is making its rounds. This fungal disease can take an otherwise green, lush lawn and transform it to a brown, blotchy mess. But by knowing the cause of necrotic ring spot and some prevention methods, you can hopefully avoid this destructive disease.
What is Necrotic Ring Spot?
Necrotic rings spot is a perennial disease, meaning it can return season after season. It mostly affects Kentucky bluegrass but can show up in annual bluegrass and some fescues as well. Homeowners often begin noticing circular rings of dead turf in their lawns around late summer. These rings, often referred to as “frog eyes” or “donut-like”, usually start out small but can eventually spread 2-3 feet. Necrotic ring spot is caused by the soil fungus Ophiosphaerella korrae which attacks and kills the grass’s roots. While the symptoms of this fungal disease aren’t usually noticed until late summer, the disease begins developing in the spring. Because of this, necrotic ring spot can be confused with other summertime turf diseases such as summer patch. A professional lawn care service is usually needed to positively identify necrotic ring spot.
What Causes Necrotic Ring Spot?
There are a few reasons a lawn might be infested with necrotic ring spot, but the biggest culprit is overwatering. Overwatering and poor drainage will allow the fungus to thrive, as well as weaken the root system of a lawn. Excessive amounts of quick-release nitrogen will also contribute to the growth of necrotic ring spot, as well as compacted soils and soils of low fertility. Finally, older varieties of Kentucky bluegrass appear to be more vulnerable to the disease, while new improved Kentucky bluegrass varieties have been breed with better resistance.
How to Avoid Necrotic Ring Spot
Necrotic ring spot is a very difficult disease to control. Most treatments and practices are aimed at minimizing and reducing outbreaks. Like all lawn diseases, prevention is the best way to avoid it. Before seeding a new lawn take some extra time to prepare the soil. Compacted, poorly-drained soils are more prone to necrotic ring spot and should be amended before seeding. When establishing a new lawn be sure to seed with only the newest, most disease-resistant Kentucky bluegrass varieties. Here at Nature’s Finest Seed, we only use varieties that have been top-rated by the National Turfgrass Evaluation Program. You may also want to consider a Kentucky bluegrass/perennial ryegrass mix, such as our Blue Ribbon Blend. Ryegrass is immune to necrotic ring spot. But perhaps the most important way to prevent necrotic ring spot is to implement responsible and efficient watering practices.
Treating A Current Outbreak
If your lawn is currently suffering from necrotic ring spot, you can speed up recovery time by amending your soil with sulfur. This can be in the form of sulfur-coated urea, or other forms of elemental sulfur. Colorado State University Extension recommends a rate of 1 to 1.5 lbs. of elemental sulfur per 1000 sq. feet per year, split over two applications. Overseeding the dead areas will also speed the recovery rate. Consider using slow-release organic fertilizers instead of quick-release synthetic types. As a last resort, fungicides can be applied. However, their effectiveness has been inconstant in studies. Timing is also crucial for fungicide applications and should be applied in the early spring. A professional lawn care service is required for this type of treatment.