Answer: Fairy rings appear in turf as circles or arcs of dark green grass, often with thin or dead grass just inside or outside the rings. They are caused by any one of more than 60 soil-inhabiting fungi that feed on decaying organic matter. The fungi releases nitrogen which causes the dark green color in the grass, however as the fungi grows it may prevent the soil from absorbing water which can result in the grass drying out.
I am not sure what benefit you would find from applying dolomitic limestone followed by an application of cupric sulfate. Limestone is sometimes applied to raise the pH of the soil and sulfur sometimes used to lower the pH. Since fairy rings are found in soils with wide ranges of pH I don't think this will solve your problem.
There is no easy or inexpensive control for this beneficial fungi. The easiest strategy is to mask the effects by fertilizing the whole yard so that the impact of the nitrogen released by the fungi is not so visible. You could remove the sod within two feet of either side of the ring, fumigate the soil, and replant with clean sod. But this seems a drastic, and temporary, solution to a minor issue. Another option is to sit back in wonder and amazement and enjoy the natural cycles of nature occurring in your yard as this beneficial fungi makes fertilizer from leaf litter right in front of your eyes!
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