Necrotic Ring Spot
Necrotic Ring spot (NRS) often appears in the spring in local Kentucky bluegrass lawns. This disease results in the formation of 'frogeye' patches of live grass within a dead circle in spring and fall. Patches may persist into the summer.
There are management practices that help suppress NRS. Fertilize moderately at the turf fertilizer rate of one pound of nitrogen per 1000 square feet. Use a product containing a mix of slow and quick release nitrogen. This avoids a flush of top growth that stresses roots. Other recommended management practices are spring or fall core aeration, avoiding over-irrigation by watering to meet ET rates and mowing at 2 1/2" to 3".
Certain bluegrass varieties, such as Adelphi, Apex, Eclipse, Nugget, Nustar and Wabash show some resistance to NRS. Consider them when seeding or sodding new lawns.
Fungicide applications may help suppress the disease although details on effectiveness of fungicide types and application timing need to be worked out. Applications should be made in spring when soil temperatures reach 65 degrees F. (mid-May). A second application in late summer or early fall is warranted on lawns with a history of NRS. The best timing of this late season application needs to be determined. See CSU Extension Fact Sheet 2.900, Necrotic Ring Spot in Turf grass, for further information.
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Updated Tuesday, October 13, 2015