This fairy ring mushroom is common in summer and fall in lawns and other grassy places. The caps are whitish with irregular patchy darker scales and may be up to 12 inches in diameter. The lower surface contains gills that change from white to gray-green as spores develop.
Fairy ring mushrooms often develop in arcs or complete rings. Generally, they first appear as a cluster of mushrooms or stimulated grass. The rings enlarge each year from a few inches to several feet. Some rings disappear for a year or more and then reappear. Fairy rings may be produced by 50 or more species of soil-inhabiting fungi.
Fairy rings are found in three general patterns:
- Mushrooms appearing in circles or arcs and lasting only for a brief time, without the presence of a dark green ring
- Stimulated grass growth producing a dark green ring, along with the presence of mushrooms
- Circular patterns of dead grass developing in the center of the dark green ring, along with the presence of mushrooms
The dark green grass is largely due to the increased amount of nitrogen that is made available to the grass roots by the fungus as it breaks down organic matter in the thatch and soil. The ring of brown or thin grass develops largely as a result of drought stress caused by the dense growth of fungal material. This weakened grass is more susceptible to environmental stresses, disease, and weed invasion.
Fairy rings are usually most severe in light-textured, low fertility soils low in moisture. The mushrooms grow on decaying organic matter and are most likely to form in turfs with a thick thatch or in areas where trees have been removed.
Control of fairy rings can be difficult. Symptoms may be suppressed by pumping large quantities of water on either side of the stimulated zone of dark green grass. A light fertilizer application during the growing season will reduce the contrast in green color between the fairy ring and the rest of the turf. Fairy rings can be physically removed by digging out the sod on either side of the dark green ring of grass and replacing it. The infested area may be killed with a herbicide and rototilled in different directions. The area can then be reseeded. Certain fungicides are labeled for use for fairy ring control. However, suppression may only be temporary.