Necrotic Ring Spot can be identified by the yellow to light-green circular patches this lawn disease causes. These patches of thinning grass range from 3 to 15 inches in diameter but can grow up to 3 feet in diameter before eventually turning brown and dying. The roots of the infected area thin and weaken, turning from brown to black. The patches often form a “frog-eye” pattern, with less susceptible types of grass surviving inside the patch's “eye.” Necrotic Ring Spot is often found in areas with a shallow layer of top soil and a hard, rocky layer of subsoil. Areas damaged by this lawn disease will pull up easily.
A Necrotic Ring Spot infection can occur only if all of the following conditions are present: 1. Pathogen: Ophiosphaerella korrae lawn fungus 2. Host: Various Bluegrass species or Fine Fescue 3. Environment: Compact, high-nitrogen soils with temperatures up to 80°F
Since you can't change your environment, the best way to control Necrotic Ring Spot is to create conditions that will foster a healthy lawn. Not only will this make your yard unfavorable for Necrotic Ring Spot growth, but it will also lower your risk of extensive damage should the lawn disease develop—plus you'll have the type of lawn you'll want to live on. For Necrotic Ring Spot control and lawn fungus treatment, TruGreen® recommends the following cultural control tips: • Raise lawn-mowing height • Reduce soil compaction and thatch with lawn aeration • Use fertilizers with moderate to high amounts of phosphorous and potash • Maintain adequate nitrogen levels using a balanced fertility program • Reduce the amount of shade in your lawn • Lightly irrigate in the mid-afternoon to cool plants and avoid drought stress