We have been digging out baseball-sized round, hard growths that we suspect are a fungus of some type. They have usually been in our lawn. One cluster was on the edge of our driveway and broke up the blacktop in that location. We now have them growing under the bluestone slabs that make up our front sidewalk. They are lifting the slabs. There are a dozen or more of them under one of the slabs. Is there anything that will kill these things? Is there a way to control them?
Baltimore County Maryland
They are a type of mushroom/fungus, and are the fruiting bodies of mycorrhizae.
You can't really kill them, but you can kick them over or remove them, but they will probably return next fall.
Though not local to us, here is a page which explains them further: