Problem type: Disease

Name of problem: Fairy Ring

Plant name(s): All turfgrasses

Symptoms / Characteristics:
Circular rings or arcs of dark green grass, yellow grass or dead grass may be evident. Arcs or complete circles of mushrooms with no noticeable effect on grass can also occur. Bands of affected grass can be 2-4" wide and form circles measuring 1-6 feet in diameter. Usually a few rings develop within the same area. Lush grass growth can occur followed by mushroom development during wet conditions.

Fairy rings are caused by a number of mushroom fungi that survive either in the soil or on leaf litter and thatch. Damage caused by fairy ring pathogens can range from little to no effect on grass growth, injured plants that will eventually recover, stimulated grass growth only, badly damaged or killed grass or the presence of mushrooms with no effect on the grass.

The fungus grows on decaying organic matter such as old tree stumps or roots and then spread in the soil or thatch layer of grass. Lush grass growth occurs due to nitrogen released as the fungus breaks down organic matter. Because of the stimulated grass growth due to the increased nitrogen availability, moisture in the soil is depleted more rapidly resulting in adjacent grasses to brown or die. This is also the reason why localized dry spots will develop around infected areas. These dry spots repel water making them very difficult to fix.

There are also several species of clump-forming mushrooms that may appear in the lawn, particularly after prolonged periods of excess moisture. These mushrooms also feed on decaying organic material but unlike fairy ring mushrooms, are not harmful to the grass. Although they are unsightly, they aid in the rapid breakdown of organic material and subsequent release of nutrients that are otherwise unavailable to plants.


Control / Preventions:
Large amounts of water can be forced deep into the soil to suppress fairy ring. Using a pitchfork or other tool, penetrate the ground to a depth of 6" about a foot away on either side of the ring, spacing holes about 10" apart and encircling the entire ring. Soak the area with water and keep saturated for about 4-6 weeks. Water should be applied to the affected area every other day to maintain this condition. Adding small amounts of liquid dish detergent to the water has proven effective.

Another means of control is to remove all infected grass and soil and replace with clean material. Fungicides have not been successful in eradicating fairy ring. Fumigants have proven effective for fairy ring control but require skilled personnel to carry out the treatments.

Unsightly clump-forming mushrooms can be removed by picking or raking as they appear. These mushrooms will likely disappear when dry conditions resume.


Photos:
fairy_ring


Relevant web sites:
www.ext.colostate.edu/PUBS/GARDEN/02908.html
www.exnet.iastate.edu/Pages/plantpath/FairyRings.html

Other references:
Couch, H.B. 1995. Diseases of Turfgrasses. Third Edition. Krieger Publishing Company, Malabar, Florida. 421 pages.