Fairy rings – they have them in Scotland, too

If you were watching the CBS broadcast of the Genesis Scottish Open golf tournament this past Sunday you might have noticed the curious circles in the fairways and greens. Is this some sort of bad feeding? Some kind of vegetative ringworm fungus? Most of all, what causes it and is it harmful?
This is a phenomenon known as “fairy rings,” and it happens when mushrooms develop on decaying organic matter, often following cool, moist seasons.

If you Google “University fairy rings in turf” you will find a dozen or more matches with prominent agricultural universities across the United States. Here is just a sampling:
Purdue University (Indiana)
https://www.extension.purdue.edu/extmedia/BP/BP-113-W.pdf
Michigan State University
https://www.canr.msu.edu/ipm/diseases/fairy-ring
Penn State University
https://turfpestlab.psu.edu/pest-profiles/fairy-ring/
North Carolina State University
https://www.turffiles.ncsu.edu/diseases-in-turf/fairy-ring-in-turf/
Colorado State University
https://planttalk.colostate.edu/topics/insects-diseases/1400-21-fairy-rings/
Kansas State University
https://www.gcsaa.org/docs/default-source/research-and-information/disease/fairy-ring-in-turfgrass.pdf?sfvrsn=2

If you care to read through these bulletins, you’ll see that there are three kinds of fairy rings. My observation has been that we most commonly have Type 3 here in Texas, where we have mushrooms developing out of the decaying organic matter in circles or part circles.
You’ll also see that all these reports tell us that control of fairy rings is difficult and that their impact of turfgrass and other plants in our landscapes is small. They say that feeding the grass adjacent to the rings will mask the fact that the actual fairy rings are usually darker green grass. To illustrate that point, I’ll refer you back to the photo beneath the Bradford pear tree above. Look closely and you’ll see arcs of darker green St. Augustine. It’s also ever so visible in the photo of the grass on the golf fairway and green.