Fairy Ring on lawns can be caused by a number of species of mushroom-forming fungi. Mushrooms are the reproductive structure of fungus that lives on organic matter, such as buried logs, lumber, roots or stumps in the soil. As they break down this organic matter, they consume nitrogen, causing the yellow rings. These fungi do not directly damage the grass, but the soil may become difficult to wet near the rings, thus stressing the turf in those areas. The Fairy Rings will usually disappear after the organic material has broken down.
Fairy Rings are circular or semicircular, and can range in size from a few centimeters up to many meters in diameter. They often appear in spring or summer. Symptoms can be variable, depending on the species of fungi, and include:
- Dark green rings with no dead turf.
- Dark green rings with a thin ring of dying or dead turf inside or outside the green ring.
- Rings of dying and dead turf with a hardened hydrophobic layer of soil that is difficult to irrigate.
- Rings of mushrooms without a visible effect on the turf. Weeds commonly invade infected areas.
- To avoid or reduce symptoms, apply adequate nitrogen and water.
- If Fairy Rings are present, aeration followed by heavy watering for several weeks may help reduce symptoms.
- 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.