The lawn fungus Ophiosphaerella korrae causes Necrotic Ring Spot, an exceedingly severe grass disease. Infection is common on high-maintenance lawns throughout the northern United States, and it is particularly harmful to Kentucky Bluegrass. Damage to your lawn or yard is common in the spring, as well as late fall to early winter. The necrotic ring spot fungus thrives in soil and affects grass plant crowns and roots. It is most frequent when rain and snow are followed by hot, dry weather.
Necrotic Ring Spot is distinguished by the yellow to light-green circular spots caused by this grass disease. These thinning grass patches range in size from 3 to 15 inches in diameter but can grow up to 3 feet in diameter before turning brown and dying. The diseased area’s roots shrink and weaken, turning brown to black. The patches frequently create a “frog-eye” pattern, with less sensitive grasses surviving within the patch. Necrotic Ring Spot is commonly seen in locations with a thin soil layer and a hard, rocky subsurface layer.
What are the Signs and Symptoms?
NRS generally happens between the months of March and May and September and November. Symptoms include dead circles or arches ranging in diameter from several inches to many feet. The illness frequently causes a frog’s eye or a doughnut to form in the lawn. A frog-eye is a tiny, circular area of green lawn surrounded by dead or dying grass. A microscopic inspection of the grass tops and leaf sheaths may indicate the presence of the fungus’s black hyphae.
On a lawn infected with the NRS fungus, brown patches with the texture of healthy grass will develop. The ideal conditions for NRS are chilly and wet, between 55 to 83 degrees Fahrenheit; however, symptoms may be more noticeable in summer hot or dry conditions.
Brown patches that resemble healthy grass
Ring-shaped brown patches that may turn light-green in the spring
The grass is simple to remove
Fungal hyphae can be seen on the roots
Treatment for Necrotic Ring Spot
Necrotic ring spot fungus in lawns can be difficult to control and can take up to 9 months to heal. The prolonged treatment period is due to the fact that it takes six months to a year to restore the soil. The necrotic ring spot fungus will continue to be an issue until microbial activity in the soil is fully restored. Patience is essential while a lawn is healing from a necrotic ring spot.
When treating Necrotic Ring Spot on a lawn, never use a fungicide. The fungicide is meant to destroy germs, and it will kill both harmful and helpful bacteria found in the soil. The long-term treatment for necrotic ring spots is to encourage a varied population of soil microorganisms. The helpful bacteria will kill the necrotic ring spot fungus spores after the soil has been restored and is teeming with microbes.
Necrotic ring spot is worse in areas with compacted soils and inadequate soil drainage. It is important to prepare the soil and ensure that the land is well drained before establishing grass. Water the lawn to a depth of 6 to 8 inches as little as possible, generally no more than twice a week, to avoid water stress. Keep the lawn at the height of 2 12 to 3 inches. At each mowing, remove no more than one-third of the blade.
