COOPERATIVE EXTENSION SERVICE Mississippi Sate University

Plant Disease Dispatch

     Most fairy rings are caused by fleshy fungi in the class Basidiomycetes, and the most common are mushrooms, toadstool, or puffballs. They occur whenever grass grows in soil that is high in organic matter.  The rings are usually marked by mushrooms or by a stimulated or depressed growth of vegetation. Three types of fairy rings are known based on symptom expression. Type I produces a distinct ring of dead grass each year and is usually visible for long periods of time. Type II produces a dark-green ring.  Type III is only visible when the fruiting bodies are produced and does not affect grass. The killing or dark-green reaction has been shown to be, in certain instances, the result of hydrogen cyanide (HCN) production. When HCN is produced in low amounts, it acts as nitrogen fertilizer; but in high concentrations, it is lethal to the grass. Fairy rings are most obvious in lawns where zones of darker green, vigorous grass occurs on either side of a zone of dead, dormant, or slower growing grass. Mushrooms may appear periodically in the vigorous outer zone. The soil beneath the depressed or dead grass is permeated by a white, fungus growth (mycelium) and the soil id usually very dry.

     Fairy rings start from the point of germination of the fungus spore (produced by the mushroom) and spread outward a few inches to a few feet per year.  Where the grass cover is not uniform, the rings may not be completely circular, resulting in crescents and interrupted rings.  As the fungus spreads outward, it consumes a portion of the organic matter in the soil, much of which is excellent as a food source for the fungus. The soil occupied by a mass of fungus prevents the penetration of water, and consequently the grass in this zone is depressed, goes dormant, or is killed from drought.  The centers of rings where grass has been killed may become invaded by weeds if the grass does not reestablish. Fairy rings survive as spores or as dormant mycelium.

     CONTROL :  Control begins in the construction or development of the lawn or fairway. Roots, stumps, branches, and other large pieces of organic debris should not be buried.  The large pieces of organic debris provide a food source for these fungi.  If the only effect of the fairy ring is a stimulation of growth in rings, fertilization will usually take care of the problem. Removal of cores of soil 1/4 to 1 inch in diameter through the zone of dense mycelium growth will aid in water penetration.  Large holes could be filled with fresh soil free of organic matter.

     Some turf experts recommend removing the soil 18 inches on each side of the outer stimulated area to a depth of one foot. In removing infested soil, it is important not to spill it on the adjacent healthy grass. Fill the trench with fresh soil and reseed or sod. Chemical control has been ineffective because the fungus grows deeply into the soil, and a lethal dose of fungicide does not come into contact with the entire fungal body.

Mukund V. Patel
Extension Plant Pathologist
09/96

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