This disease is caused by “Toadstool” or “Mushroom” type fungi. It usually appears in early Summer. On first impression, you think of Brown Patch Fungus, since it was present just earlier in the Spring. Even though Fairy Ring Fungus is similar to Brown Patch in appearance, it is treated differently. Normally, these are dead, incomplete circular areas or crescent shapes, sometimes with a line of toadstools and a narrow band of green grass in the leading edge of the crescent shapes. These areas are permanent and occur in the same spot year after year.
The fungal mycelium (or threads) concentrates in these dead areas in the soil and forms a mat that does not allow water to penetrate. This causes the lawn to dry out and die. Also, this entire complex moves in the direction of the leading edge each year, slowly, and will eventually move off the area after many years. The fungus actually feeds on organic matter present in the soil and does not directly attack the lawn.
At present time, there are no chemicals available to control Fairy Ring Fungus. You can lessen the severity of this disease by injecting water into the ground and by core aeration. Anything you do to add moisture or air to these areas will help. It is best to keep fertility levels high.