Our corn had it back in 2017, didn't do anything to the bed afterwards and have grown corn in the same place a few times since but haven't found it again.
Re eating - it's also known as Corn Truffles and is a bit of a Goldilocks fungus. The younger, harder fruit bodies aren't eaten as they're too tough (and probably difficult to digest). The older, softest parts are already too sooty and don't make good eating - the insides have a powdery texture and make your mouth black. It's the bits in between that are just right.
Once cooked (we fried them in butter) they have a pleasant shroomy, sweetcorn flavour. Ours topped an open toasted sourdough sandwich with cheese, tomatoes and a drizzle of olive oil.
