David M. Kopec, Extension Turfgrass Specialist
Many people have seen the ubiquitous rings that appear in lawns in many parts of the country and here in Arizona. We are talking about the large, distinct rings that make the grass green! There are many interpretations as to what the rings actually are and what causes them. In most cases, when the rings are more than two and one-half feet in diameter, they are called FAIRY RINGS. The ring is not an excessive problem unless the lawn is under fertilized. In this case, the ring will stand out like a sore thumb in contrast to the dying turf at the edge caused by an hydrophobic soil. How did the name fairy ring originate? At one time, it was believed that fairies from the woods would come out at night and dance in circles. The fairies would dance around and around until they made a "ring" in the grass. Science believes that there is another culprit.
Fairy rings are caused by a group of underground fungi that are related to the wood-rot fungus. The fungus starts as one tiny spore under the lawn. As it grows, it eats what little organic matter is in the soil. Since the fungus is not 100% efficient in doing so, it leaves behind some waste (unused protein). This protein is converted to nitrogen, and thus- - greener turf. Each year, the "ring" gets wider and wider, as the body of the fungus grows. Fairy rings can occur on any type of lawn. In fact, if you're ever in an airplane and fly over large pasture fields, you can sometimes see very large rings that are unnoticeable from the ground!
In addition to the green ring, which may make the lawn look uneven, there is sometimes a bare area either on the outside or inside of the green ring itself. This is caused by either the fungi releasing a temporary toxin, or the mycelial mat itself repelling water. The repelling of water is more prevalent! If you take a pick to the edge of the ring, look at the soil clods that come up. You may see a white spider web throughout the soil (mycelium). This is the underground body of the fungus. Sometimes, but not always, you may see toadstools associated with the ring along the edges. Toadstools occur under ideal temperature and moisture conditions. Sometimes you may see a ring of toadstools, but NO green ring. In this case, just forget about it! Don't eat these mushrooms! They're deadly!
What to do about it...?
Unsuccessful remedies include throwing boiling water on the ring, adding motor oil with water, or pouring vinegar on the ring. Some people will go to the task of digging out the ring and replanting. Don't try these.
If the lawn is actively growing (not sleeping or stressed from heat/drought) you can "hide" the ring by applying fertilizer on and around it, or fertilizing the entire lawn. The added nitrogen from the fertilizer makes the surrounding grass green. This helps mask the green that occurs from the fairy ring. For bermudagrass or an overseeded lawn, you can apply nitrogen from early spring to August. If you want to avoid extra mowing, add iron instead of nitrogen to green up the lawn. If you have a tall fescue lawn (especially at low elevations), you should not fertilize it with nitrogen past the end of April. The same applies for Kentucky bluegrass in the high country. Nitrogen applications will weaken the lawn, increasing summer stress. Instead, apply iron to the lawn to make it green.
To get the "ring" to accept water, hand water using a garden hose. Take a close tine pitch fork and poke holes all around the ring. Apply a wetting agent, or make your own by adding one tablespoon of liquid detergent to five gallons of water. Slowly pour it over the ring and into the holes. The following day, water the area again by hand, using a garden hose.
If your fairy rings are bad and the above remedies are ineffective, you may want a certified applicator to apply a special fungicide called "Prostar" (flutolanil). Have it applied as a soil drench around the ring.
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director, Cooperative Extension, College of Agriculture & Life Sciences, The University of Arizona. The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.