Necrotic Ring Spot

Management practices that reduce stress on turf grass, such as watering turf to avoid drought stress, will also help suppress necrotic ring spot. Normally, lawns should be watered deeply and as infrequently as possible without creating stress from over-watering. In the presence of necrotic ring spot, however, frequent watering will cool the grass and allow infected plants with depleted root systems to survive the late afternoon heat. Light applications of water can be applied daily to infected turf in hot weather to reduce heat stress and initiate recovery. Care should be taken to prevent over-watering. Compacted soils are more favorable for this disease to occur as well. Thus core-aeration, with clean equipment, will help minimize soil compaction. Avoid nutrient deficiencies and maintain a balanced fertilization program, particularly for nitrogen, phosphorus, and potassium.

Lawns should be cut so the grass is 2.5 to 3.5 inches high. There are no varieties of Poa pratensis turf that offer complete resistance to this disease. Some varieties of Kentucky bluegrass have more tolerance than others. Kentucky bluegrass seed advertised as “disease resistant” may be somewhat resistant to necrotic ring spot. Planting mixtures of two or more grass species and two or more resistant cultivars will reduce the possibility of disease. Existing areas of infected grass can be over-seeded with resistant varieties to reduce the inci­dence of necrotic ring spot. Another option is to over­seed the area with perennial ryegrass (Lolium perenne) which is reported to be immune to NRS.

Homeowners should be aware that different grass species and mixtures often results in color and textural differences; however, perennial ryegrass mixtures with Kentucky bluegrass are very desirable and will help to avoid nectrotic ring spot. Researchers in Colorado have noted that control of this disease using fungicides has been erratic.