Fairy Ring

Fairy ring is caused by a number of species of mushroom-forming fungi including many basidiomycetes in the order Agaricales. For example, Lepiota spp. are common in southern California, Marasmius oreades has been found in central and northern California, and Agrocybe pediades occurs in both southern and northern California. Many of these fungi are poisonous and must not be eaten.

Fairy rings are circular or semi-circular and can range in size from a few centimeters up to many meters in diameter. Symptoms can be variable, depending on the species of fungi, and include: 1) dark green rings with no dead turf; 2) dark green rings with a thin ring of dying or dead turf inside or outside the green ring; 3) rings of dying and dead turf with a hardened hydrophobic layer of soil that is difficult to irrigate; and 4) rings of mushrooms without a visible effect on the turf. Weeds commonly invade infested areas.

There are two types of fairy rings, edaphic (non-superficial) or lectophilic (superficial). Edaphic rings are generally formed by fungi that inhabit the soil underneath the turf. These frequently cause a hardened hydrophobic layer of soil above the areas of their active growth that prevents water penetration into the soil and often causes plant death. Rings of dead turf are frequently associated with this type.

Lectophilic rings are caused by fungi that inhabit the thatch layer and decomposed plant debris, litter, and old thatch. These rings are characterized by a slight depression of the affected areas surrounded by dark green rings of turfgrass where the fungi are breaking down plant material and releasing nitrogen. A hard, hydrophobic soil layer is not associated with this type of fairy ring.

The fungus survives as a white mass of mycelia in the soil or thatch layer, or can be spread by spores dispersed by the mushrooms produced by the rings. In some cases, rings or mushrooms can appear in the turfgrass and cause no apparent damage.

All grasses are susceptible to fairy ring.

A dense thatch layer contributes to the availability of undecomposed matter, as does the addition of composts or other organic material that have not been fully decomposed. Also, turfgrass growing in low fertility soils with insufficient irrigation appears to suffer more damage from fairy rings than turfgrass with adequate fertility and irrigation.

A turfgrass management program that provides proper fertilization and irrigation along with regular dethatching of the turfgrass will help prevent the development of this disease. Fungicide treatment or soil removal may be necessary if fairy ring becomes a problem.

To avoid or reduce symptoms, apply adequate nitrogen and water. Symptoms of superficial rings can be masked by nitrogen applications. If fairy rings are present, aeration followed by heavy watering for several weeks may help reduce symptoms; soil wetting agents may improve water penetration. Proper thatch management and regular dethatching can contribute to a reduction in the disease. Fairy ring can be eliminated by removing the turf and root zone with the soil containing the white, cottony, mycelial mass. If fairy ring symptoms consist only of mushrooms and there is no zone of dark green grass, the mushrooms can be raked off and disposed of. While this will not weaken or control the fungus, it will improve the turf's appearance.

Fungicide applications of azoxystrobin appear to provide good control of the disease when used properly. Flutolanil applications provide some suppression; control may be improved if applications are used in conjunction with cultural practices.