any of numerous mushrooms of meadows and open woods, especially the well-known Marasmius oreades, that spread in rings originating from mycelial growth: formerly supposed to mark the paths laid by dancing fairies.
fairy ring disease of cranberry: causal agent and life cycle determined.
fairy ring is a serious fungal disease of cranberry that kills vines and is difficult to control.
British Dictionary definitions for fairy ring
a ring of dark luxuriant vegetation in grassy ground corresponding to the edge of an underground fungal mycelium: popularly associated with the dancing of fairies: seasonally marked by a ring of mushrooms
short for fairy ring mushroom, Marasmius oreades, a dainty buff-coloured edible basidiomycetous fungus, characteristically forming rings in grassland