We get dead circles in our grass. Inside the circle, the grass looks fine. We have had the grass replaced, aerated, and seeded, yet the problem keeps returning. How do we fix this?
The symptoms you describe are characteristic of yellow patch (caused by a Rhizoctonia fungus), sometimes known as “frog eye” or “summer patch.” It occurs during hot, dry and windy weather near the end of summer. Drought-stressed, shallow-rooted Kentucky bluegrass lawns are the most susceptible. It often shows up near paving or parts of the lawn that dry out first.
You need to review your lawn maintenance and cultural practices. Overuse of nitrogen fertilizers and excess thatch can make the problem worse. By aerating, you have taken a step to reduce thatch and improve water penetration. Make very sure that your mower blades are sharp, and that the grass is mowed no shorter than 2-1/2 inches. Mowing too short sets the lawn up for weeds and further disease. When you water, water deeply to wet the entire root zone and water consistently. Do not let the turf dry out. Betting on Mother Nature to be cooperative with her rain showers can often make the homeowner the loser in the “turf stakes.” Apply less nitrogen, particularly in midsummer, on Kentucky bluegrass lawns.
If you find you must reseed, select resistant varieties. Studies have also shown that simply adding a small percentage of perennial ryegrass to bluegrass can greatly reduce the problem.