Description

Symptoms of this root disease usually manifest themselves during the first occurrence of dry soils.

The disease appears first as bluish-green, wilted grass in patches one-half-foot to three feet in size. These patches quickly become brown as the wilted grass dies. Often, a tuft or patch of healthy turf is present in the center of affected patches, giving the turf a "donut" or "frog-eye" appearance. Below ground, roots of affected tillers have a light brown to dark brown decay.

Symptoms are most severe in the driest parts of the landscape, such as on knolls or slopes. Although symptoms of necrotic ring spot generally develop in early summer, they can persist throughout summer until cool weather allows the turf to begin to recover.

Favorable Conditions

Active in low temperatures, symptoms appear in warm, dry periods.

Susceptible Grasses

Annual Bluegrass, Kentucky Bluegrass, and Fine Fescues.

Management Recommendations

Control thatch buildup to promote lawn health.

Ensure adequate amounts of phosphorous and potassium and slow release nitrogen.

Irrigate to prevent drought stress. Although deep and infrequent irrigation is recommended for management of most turf diseases, light and frequent irrigation can promote survival after an outbreak of necrotic ring spot, since the disease results in a shallow root system. It may also help to apply this irrigation during the hottest part of the day.

Maintain a mowing height no lower than two inches.

Overseed affected areas with perennial ryegrass or renovate with resistant varieties of Kentucky bluegrass or with tall fescue. The Kentucky bluegrass cultivars Adelphi, Classic and Nugget did not show susceptibility towards NRS in cultivar trials conducted in the United States.