You may see circular areas of diseased turf during late summer. These are called fairy rings. The following is more information.
Fairy Rings in Turf
This disease, caused by a group of fungi known as basidiomycetes, is visible on many golf greens and home lawns in late summer. Symptoms typically appear as continuous or interrupted rings of dark-green turf. Mushrooms, which are often associated with fairy ring, usually develop in the spring and fall. Although fungicides are not effective against all species of the fungi that cause fairy ring, Bayleton, Headway, Heritage, Insignia and Prostar have provided good control in many university tests. For best results, maintain adequate soil moisture and fertility to mask symptom expression. Spike affected turf prior to irrigation and the application of fungicides to enhance water movement into the soil profile. The use of surfactants may enhance fungicide efficacy and aid in symptom suppression.
Fairy rings. Photo by Lester E. Dickens, Bugwood.org
Information taken from the August 21, 2008 edition of the Plant & Pest Advisory, Landscape, Nursery & Turf Edition, from Rutgers University.