FAIRY RING ON TURFGRASS Various basidiomycetes   F A C T S H E E T

Introduction

During the spring or summer a circle or arc of stimulated grass or of toadstools may appear in lawns. These are turf abnormalities called fairy rings. The rings can be from a few centimeters to 20 meters in diameter, but most are between 0.5 m and 5 m across. These rings of lush growth in the lawn are caused by the release of nutrients, in particular nitrogen, from the activity of the fungus living on organic matter in the soil. These causal organisms are mushroom- or puffball-forming fungi. Some mushrooms or puffballs are very poisonous when eaten and it is, therefore, important that they be routinely destroyed if small children are likely to be attracted to them.

Symptoms

There are three kinds of fairy rings. One type has no mushrooms; stimulated grass growth reveals the activity of these fungi in soil (Fig. 1). Another type contains a ring of mushrooms as well as a ring of stimulated grass growth. A third type contains only a ring of mushrooms, with no evidence of unusual grass growth (Fig. 2).

Figure 1: Symptoms may include variously sized dark green circles of quickly growing grass. (provided by Dr. Eric B. Nelson, Cornell University) Figure 2: A circle of mushrooms is a classic symptom. (provided by Dr. Eric B. Nelson, Cornell University)

Fairy rings usually do not present a lethal threat to a lawn or other turf, but sometimes a ring of dead grass occurs in addition to the ring of stimulated grass growth. Death in the ring is due to the interference with normal penetration of water by the dense mat of fungus mycelium in the soil, to toxic substances given off by the fungus in the soil, and possibly to direct effects of the fungi on the grass plants. Fairy rings normally reoccur each year, and their diameter slowly increases.

Disease Cycle

Small rings appear as the intial symptoms of the infection. The rings become larger each year as the fungus grows in radial pattern. Rings can increase in size up to 0.5 m annually and can become quite large after years of infections.

Management Strategies

If the fairy ring consists only of mushrooms or puffballs, with no stimulated grass growth, simply rake off and dispose of these fungal fruiting structures. If handling the mushrooms, wash your hands when done.

As serious injury to the turf does not occur often with fairy rings, the most practical method of dealing with them in lawns is through a cosmetic approach. Disguise the symptoms by providing adequate water deep into the root zone, and by applying moderate rates of fertilizers. This will increase the vigor of the surrounding grass to the level more like that of the grass in the fairy ring. Excessive application of water or fertilzer should be avoided as either may contribute to other turf diseases or stimulate fairy ring development. More frequent mowing may make the difference in height between grass of the fairy ring and adjacent grass less conspicuous.

In rare cases where complete eradication of a fairy ring is necessary, the sod and underlying soil in a band 40 to 55 cm in front of and in back of the ring can be removed to a depth of 20 to 90 cm, depending on the extent of the development of the ring. The resulting hole should be replaced with clean, preferably sterilized, topsoil or soil mix. New sod or seed can then be established where the fairy ring was removed. Soil fumigants are sometimes effective for eliminating fairy rings, but this treatment must only be done by a licensed pest control applicator who is qualified to safely use toxic fumigants.

Some fungicides are available to treat some fairy rings, but this is discouraged in home lawns and should only be considered where mushrooms are being produced and have been accurately identified. In New York State, except for Long Island, Prostar 70 WP can be used to treat fairy rings on turf caused by Marasmius spp., Lepiota spp., or Agaricus spp.; Heritage may be used to treat fairy rings caused by: Lycoperdon spp., Agrocybe pediates, or Bovistra plumbea. Follow label directions. Use only if other management practices do not provide adequate suppression, and use only to treat fairy rings caused by the genera listed on the label. It is not necessary to treat the entire lawn. Treat only the affected area and the lawn within a few feet of the ring. For best control, use in conjunction with cosmetic approach described above.

Updated, SLJ, 3/09