Never underestimate WD40.

I once had a large fairy ring in the front garden, about 12' across. I
sprayed the heads with WD40, and then again after about a week.

In the autumn they made a reappearance, and got the same treatment.
The following spring the survivors got another dose, and that was it.
They disappeared never to return.

It was a*lot* easier than digging up the soil, getting rid of it, and
refilling the hole and replanting.

TF

Don