Problem: Necrotic Ring Spot
Caused by the fungus Leptosphaeria korrae, this disease occurs from March through November. It appears most frequently in spring and fall when hot, dry conditions follow cool weather. Dense turf with excessive thatch buildup is especially susceptible. Necrotic ring spot is most prevalent in compacted soils and heavily thatched lawns, especially on exposed sites and steep slopes. It can affect most types of lawn grasses, including bentgrass, bermudagrass, Kentucky and annual bluegrass, centipedegrass, fescues, ryegrass, and zoysiagrass.
Dense turf with excessive thatch buildup is especially susceptible to necrotic ring spot. Dethatching and regular aeration help prevent this disease. Avoid drought stress, and apply the required amounts of fertilizer. During hot summer months, leave the blades a little longer than in cool periods. Fertilize regularly to encourage the lawn to fill in. Reseed any seriously affected areas.