Fairy rings are reported to be caused by many (60) different soil-inhabiting fungi of the class Basidiomycetes. These fungi can cause the development of rings or arcs of deep green grass as well as unthrifty or dead grass. Rings may vary in size from a few inches to 200 feet (60 meters) or more in diameter with an annual radial growth of 3 inches (7.6 cm) to 19 inches (48 cm) depending on grass, soil and weather conditions. The term fairy ring' has its origin in myth and superstition as they were believed to be the result of a circle of dancing pixies (fairies'). These circular rings were also thought to be the result of lighting strikes and where the devil churned his butter. Today's research community has shown the dark green circles are the result of fungi colonizing the soil, leaf litter or thatch. The break down of organic matter by fungal activity releases nitrogen stimulating grass on the outside of the ring causing it to grow taller and darker than surrounding grass. The band of stimulated grass is often associated with the fruiting bodies of the fungus. The fruiting bodies range in size from 3/8 inch (1 cm) to 12 inches (30 cm) in diameter. Some of these so-called mushrooms',toadstools' and `puffballs' are poisonous and are best picked and disposed of if young children frequent the area. Removing these fruiting bodies does not weaken the fungus but does help improve the aesthetics of the area.

Spread and Development:
Fairy ring starts from a piece of mycelium or spore at a single point feeding as a saprophyte in the thatch layer or on soil organic matter. The uniform outward growth of the fungus results in the development of rings. Changing soil types, the fungus involved, condition of the turf, abundance and type of organic matter and obstructions all affect this radial growth. Fairy rings encountering each other in their development will typically produce a scalloped effect of stimulated or dead grass. This condition is thought to be due to chemicals (metabolites) produced by the fungus inhibiting the growth of other fungi. This inhibition is called `fungistatis'. A similar condition is thought to occur on slopes, where the lower part of the ring breaks possibly due to the downward movement of these self-inhibiting metabolites. These substances are thought to prevent the growth of the fairy ring fungus in the turf at the lower part of the ring. Under certain conditions, and with certain fairy ring fungi, a ring of dead grass develops. Some of the responsible fungi have been shown to penetrate and kill root cells resulting in dead rings of grass. In addition, the mycelium of some fairy ring fungi are reported to be hydrophobic, creating a water-impervious layer resulting in drought-stress problems for the grass. Once the soil under this mycelial layer becomes dry it is very difficult to wet and the roots of the grass plant die. Some fairy ring fungi stimulate the grass but do not cause its death. The development of other fungi result in no stimulation or damage of any sort. Instead, a ring of mushrooms is the only indication of the presence of the fairy ring fungus. Depending on environmental conditions, several years may pass without the production of mushrooms. The presence of dark green or dead rings may themselves be lacking. Turf subjected to extreme drought stress is more susceptible to problems from fairy ring.

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