Grass Is Dying in Circles

By Home & Garden Last updated Sunday, July/07/2024

Necrotic Ring Spot

This disease, primarily affecting Kentucky bluegrass, is caused by the fungus Leptosphaeria korrae. The first signs of necrotic ring spot are rings between 6 inches and 2 feet in diameter, with thatch decomposition in the vicinity. If affected in spring or fall, the weakened plants are especially susceptible to drought and the heat of summer. Once established, the disease is hard to control and damage may be ongoing for several years. Treatment includes a combination of fungicides, aeration to lessen soil compaction, controlling thatch and adjusting water and fertilizer use. Top dress, or spread thin layers of soil on the lawn, to remove excessive thatch. Use only small amounts of nitrogen fertilizer and keep the area wellirrigated in hot weather.

Caused by the Lanza or Moellerodiscus fungus, lawns afflicted with Sclerotinia dollar spot
develop circular yellow areas up to 2 feet in diameter. When the grass is initially affected, leaves may develop a red-brown border. When there is dew on the grass in the early morning, these plants are covered with a cobweblike material. Prevention is the best cure, so keep the lawn well-fertilized and watered. If the disease develops, apply the appropriate fungicide.

Despite the cute name, fairy ring can devastate a lawn. At least 50 types of fungi may be responsible for the tell-tale fairy ring, which may include mushrooms around the circle. The most common culprit is the Marasmius oreades fungus. Keeping your lawn well-maintained and adequately watered and fertilized can deter the growth of fungus causing fairy rings. These rings grow out from a central point, progressing between 1 and 2 feet annually. If you have a small property, these rings can intrude on a neighbor's lawn relatively quickly if nothing is done. Although time-consuming, digging out the area is the most effective treatment.

Also primarily affecting Kentucky bluegrass, this disease is more prevalent in cool, rainy weather and is caused by Rhizoctonia cerealis fungus. In its initial stages, it appears as small patches of yellowish grass, which soon turn brown and grow into circles of up to 2 feet. Treatment is similar to that of necrotic ring spot, but there are no effective fungicides for this disease.