Question
I have brown, perfectly round circles in my yard and we have not had rain in weeks so it is not fungus. The grass does not pull out easily nor is it wet or slimy. It looks like mini crop circles about 1 foot to 2 feet in diameter with green grass in the center. Any ideas?

Answer
Mike:

The damage to turf sounds like fungus, though it may not be active.  The fungal activity can cause delayed results.

From your description, it could be Fusarium blight, Rhizoctonia (yellow or brown), necrotic ring spot or summer patch.

More importantly, reduce nitrogen application in the spring, favor fall and winter apps.  Reduce thatch build up, if that is a problem, less than 1/2 inch is recommended.  Aerate to reduce compaction.  Alter watering practices to favor deep watering infrequently, rather than frequent light waterings.

You may treat with a fungicide, though Yellow Rhizoctonia will not respond to this.  But focus on cultural practices to reduce the favorable environment for fungus.

In the fall, you may apply a high quality compost to the lawn.  I define high quality as thermophilically produced (above 131 deg. F) with good nutrient make up (1.5-3 % N, 1-4 % P, 1-2 % K) and fine particle size.  Should smell like rich soil or woods soil and be brown to black in color.

Apply at 2/3 to 1 cubic yard per thousand square feet of lawn.  A high temperature produced compost is, usually, antifungal.  Nutrients are released over time as plants demand them, rather than force feeding them with soluble compounds.

Best wishes.