What are the brown circles in my lawn?
The brown patches or circular rings in your lawn are probably a fungal disease called brown patch. This disease develops under high humidity after the spring climate begins to warm.
"While the soil-borne Rhizoctonia fungus is present all year, certain conditions are needed for disease to occur. Most important are extended dew periods or rains and the disease is often worse in low, wet areas. Relatively cool temperatures, from 60-75 degrees F, facilitate the disease. At temperatures of 75 degrees F and above, and under low-moisture conditions, the activity of the fungus decreases. High nitrogen fertility increases turf susceptibility to the disease.
"The first symptom of Brown patch is one or more light green patches that may range in diameter from 2 inches to about 2 feet. The patches grow from the center outward and may spread rapidly. Patches grow as long as conditions are favorable and may spread out 20 feet or more. In the fall, patch borders are usually brownish to gray. In the spring, as the grass starts to grow and if the weather remains wet and mild, the patch may turn yellow, gray, and then brown."
The text above is copied from "The Plant Doctor: Brown Patch, Large Patch, or Rhizoctonia Blight of Warm-Season Turf Grasses) found online at http://msucares.com/pubs/infosheets/is1669.pdf. It is authored by Alan Henn, associate Extension professor, Entomology and Plant Pathology, Mississippi State University.
An approved fungicide, combined with proper watering techniques, should return lawns to normal within a couple of weeks.
A sample submitted to a diagnostic lab will confirm the presence of brown patch in your lawn.
Contact your county Extension office for fungicide recommendations and procedures for submitting samples to a diagnostic lab.