Lawn Disease: Necrotic Ring Spot

Every year we see more lawns suffering from a soil-borne fungus called Necrotic Ring Spot. The name comes from the dead or yellow “rings” that appear in the lawn. Unlike fairy ring, which have a dark green ring, necrotic ring spot kills the grass. This fungus, however, only affects Kentucky bluegrass. Unfortunately, once it appears in your lawn, it has already been there for two or three years.

NRS can be seen during the growing season, but is more commonly identified in late July or August. Once established, it is very difficult to manage, and at times is impossible to correct without lawn renovation. If not properly maintained, NRS can spread throughout your lawn.

Often, the cause is preventable. As homeowners, we tend to overwater and overfertilize the lawn when these rings appear. By watering properly and fertilizing at timed intervals, you take the greatest step in preventing an outbreak. Also, keep your lawn cut at 3 inches; cutting your lawn short gives this disease a great area to grow. As NRS is a perennial problem, once it starts, it will be back year after year without intervention.

Managing a lawn with NRS is all about education. Knowing that watering, fertilizing and mowing are the biggest steps in controlling this disease, homeowners can adjust what they do to suppress it. No chemical on the market will eradicate NRS, so there is no quick fix. However, there are some bluegrass varieties that are resistant to the NRS. And if a large outbreak happens in your yard, it is wise to renovate or overseed with one of these varieties (A list of NRS-resistent varieties will be detailed below).

Try the following practices to improve you chances from getting NRS:

  • Core aerate once a year. This avoids compaction and increases root vigor.
  • Do not overwater. Water infrequently as possible without causing lawn stress.  Water when the lawn needs it.
  • Proper mowing. Mow to a height of 2 1/2 to 3 inches.
  • Fertilize at timed intervals. It is recommended to fertilize every six to seven weeks. When hot, fertilize with a slow release fertilizer.
  • Use a NRS-resistant turf.  Resistant bluegrass varieties, ryegrass or fescue are the most effective against NRS.

As this is becoming one of the most serious problems in the turf, we have adjusted our programs so that your lawn maintains a beautiful look without contributing to Necrotic Ring Spot.

If you have anymore questions, Colorado State University has a fact sheet that details NRS more fully. Also, feel free to call Ferta-Lawn with any questions. One of our lawn technicians will be able to discuss your individual needs.

Resistant varieties of Kentucky bluegrass:

  • Adelphi, Alpine, Apex, Award, Bristol, Classic, Eclipse, Impact, Kelly, Joy, Liberator, Midnight, Miranda, Mystic, NuBlue, Nugget, NewStar, Odyssey, P105, P104, Unique, Wabash and Washington.

Your local nursery or garden center will be able to help you with resistant varieties that are effective in your exact location.


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