Necrotic ring spot shows up as circular or doughnut-shaped patches of light green to straw-colored grass. Older patches appear as a “frog eye”, with healthy grass in the center encircled by a ring of dead grass. These diseased rings can vary in size from several inches to several feet in diameter. Over time, the affected grass dies and becomes matted and rings may coalesce to create larger arcs of dead turf.
Susceptible species: Kentucky bluegrass and fine fescue; occasionally annual bluegrass, creeping fescue, and bentgrass.
Favorable conditions: Necrotic ring spot commonly occurs when wet weather is followed by hot, dry periods. However, necrotic ring spot can occur over a broad range of temperatures and soil moisture conditions, and therefore can occur from mid-spring through late fall. If left untreated for several years, necrotic ring spot incidence will naturally decline.
Recommended cultural practices:
Chemical control: Preventative treatment in the spring using systemic fungicides can be effective in controlling necrotic ring spot.
Photo Credit: Mary Ann Hansen, Virginia Polytechnic Institute and State University, Bugwood.org