University of Illinois Extension
Bruce Spangeberg

These articles are written to apply to the northeastern corner of Illinois. Problems and timing may not apply outside of this area.

Stateline Yard & Garden

Large Circles in Lawns May Be Fairy Ring

July 15, 1999

Ever noticed large circles or arcs of dark green, lush, fast growing grass in a lawn or turf area? Perhaps you’ve seen large arcs of brown or dead grass? Under wet conditions, maybe you’ve seen a circle of mushrooms appear in a turf area. These are all examples of fairy ring.

Fairy ring fungi are not attacking the grass directly, but are breaking down organic matter in the soil. As a result, nitrogen is released that the grass above may use, causing the green ring. If mycelia of the fungus get very dense and inhibit water movement into the soil, grass in the arc may turn brown. Mycelia may also deplete soil nutrients and produce toxic levels of hydrogen cyanide. The mushrooms that appear after rainfall are the fruiting bodies of the fungus.

Why do some lawns get fairy ring? The "food" source is often old tree stumps, roots, logs, lumber, and other larger pieces of organic material in the soil below the lawn. Once this material is depleted, the fairy ring will disappear. This may take considerable time. Several fairy rings may appear relatively close together, especially on lawns that exist on sites that were previously wooded areas. When this occurs, you’ll notice the rings do not cross each other, as fungus activity ceases when fungi from different rings contact each other.

There are several ways to manage fairy ring. If the lawn has not been planted yet, be sure to remove tree stumps, large roots or construction lumber buried in the area.

When renovating a turf area that previously had fairy ring, be sure to blend all soil together, as different fairy ring fungi will attack each other. If several rings are visible at the time of renovation, collect the white mycelia from each and mix it together, then spread over the soil and work it in.

Most often, fairy ring appears as the green arcs in established lawns. This can be masked somewhat by increased watering and fertilizing of the grass, keeping within suggested lawn care guidelines. Lawns watered and fertilized on a regular basis tend to have fewer problems with fairy ring. Delay fertilizing until about Labor Day, however. In addition, large quantities of water may be pumped into the soil in and around the rings using a root-feeder attachment to a garden hose.

 

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