My Lawn Has Large Black Rings Which Turn Brown & Die

Necrotic Ring Spot

• Necrotic ring spot is a disease caused by the fungus Leptosphaeria korrae, which is most active during the spring and fall months. This fungal disease produces symptoms such as black rings on lawn grass, which typically measure from 6 to 24 inches in diameter. These black rings take on the characteristic "frogs-eye" pattern and have a sunken appearance. The roots of the grass are covered with black strands of fungus, which causes the grass to turn brown and die.

Management

• Managing necrotic ring spot in lawn grass is best accomplished by aerating the soil, mowing grass frequently and adjusting watering practices. If your lawn has symptoms of necrotic ring spot, it is best to provide frequent, light waterings. This keeps the top 2 inches of soil moist and reduces drought stress. Avoid using lawn fertilizers with high levels of nitrogen during the spring. According to North Dakota State University, one pound of nitrogen fertilizer per 1,000 feet of grass should be applied in the fall or the early part of September. Another application is necessary when the lawn goes dormant in the fall or late October to early November. Applications of fungicides may be helpful in reducing the symptoms associated with this lawn disease. Fungicides work best if applied before the disease is severe.

Rhizoctonia Blight

• A hot weather disease that is often severe on lawns is Rhizoctonia blight, also known as brown patch. Rhizoctonia blight is caused by the fungus Rhizoctonia solani, which is responsible for large, black rings on lawns. These patches are often 1 to 3 feet in diameter and appear black. Later in the day, these black water-soaked patches turn light brown in color as they dry. Rhizoctonia blight is most severe in warm, humid temperatures. Daytime temperatures between 80 to 90 degrees and nighttime temperatures above 70 degrees favor the development of this fungal disease.

Rhizoctonia Blight Control

• Avoid using fertilizers with high levels of nitrogen, especially before periods of hot, humid weather. Homeowners who have noticed symptoms of Rhizoctonia blight on their lawn may wish to apply a fungicide before hot weather periods. This can prevent a severe outbreak of this disease if the weather favors its development.