Fairy rings are patches, arcs, and sometimes lines of dark green, fast growing turf or occasionally dead turf. Fairy rings may or may not be accompanied by mushrooms. The fungi are not infecting the turf but instead are living on dead organic material in the soil or thatch, including buried wood, tree stumps, peat, or even thatch. The dark green color results from the release of nitrogen brought about by the decaying action of the fungi on the dead organic matter in the soil.
Chemicals are generally ineffective in controlling the disease and are at best short-term solutions.
If the cause is a buried tree stump or other solid wood debris, remove the wood and replace with soil. If the organic matter is peat or another non-discrete source of organic matter there is not much that can be done. The dark green color can be masked by applying nitrogen or iron to the entire turf stand. All grass species and varieties are equally at risk.