Lawn Necrotic Ring Spot

necrotic ring spot on grassQuestion: I am hoping you are the correct person to contact with my lawn problem.  I have Necrotic Ring Spot on my lawn.  I am looking for advice of handling this disease. Any information would greatly be appreciated. B.T.

Answer: On the same day I received your email the Kenosha County UW-Extension horticulture helpdesk master gardeners got a photo of a home lawn with light brown circles. Necrotic Ring Spot and Summer Patch are two different diseases caused by different fungi. Both diseases cause circular or ring patterns of tan grass in the lawn.  Turfgrass diseases are notoriously difficult to diagnosis, even for professionals, so I can’t tell for sure which disease is causing the rings.

Regardless of the type of disease, home lawns should be treated with a combination of good cultural practices and re-seeding with disease resistant grass cultivars. Irrigate deeply – so the soil is wet 3 to 4 inches deep – once a week preferably in the morning. Two to three times per year (Memorial Day, Labor Day, Columbus Day) apply a fertilizer containing at least 35-percent slow release nitrogen. If you don’t leave the clippings on the lawn, which is recommended, add a fourth fertilization around Independence Day. Keep the mowing height at 3 to 3 1/2 inches. The longer the grass blade is the deeper the roots. Core aerate in May or September to decrease thatch and encourage deeper rooting.  Necrotic ring spot often disappears on its own after a few years of proper care.  Disease resistant cultivars are available for necrotic ring spot and summer patch. In mid to late August rake out dead grass and re-seed with resistant cultivars of Kentucky bluegrass.

I don’t recommend fungicides for home lawns. If you decide to use a fungicide, the cause of the lawn problem should be confirmed by a turfgrass lab before treatment. Send a lawn sample to the University of Wisconsin Turfgrass Diagnostic Lab in Verona. The cost is $20 for home lawn samples. Their website at will give you information on what and how to send your sample. The lab will culture your sample, give you a diagnosis, and suggest treatments. Fungicides are preventative and will not cure already diseased grass.

2014 Master Gardener Training Orientation will be held August 5th beginning at 6:00 p.m. at the Kenosha County Center, 19600 75th Street in Bristol. Orientation is an opportunity to learn more about the Master Gardener Volunteer Program. For more information 262-857-1945 or


Barb Larson is horticulture educator for Kenosha County University of Wisconsin Extension. Barb has a Master’s of Science in horticulture from the University of Wisconsin-Madison. If you have a plant or gardening question, email Larson at or call her at 262-857-1942.