Lawn mushrooms are simply the product of fungi infested in your yard's soil. They are actually the fruit of this fungus, and feed off different sources that could be present. Lawn mushrooms feed off decaying matter.
In addition to Fairy Rings, various other mushrooms may appear in lawns, but don't injure the grass. However they may be unsightly and cause people to worry that children or pets may eat them. Some lawn mushrooms are poisonous to very poisonous others are not poisonous. There is no way to distinguish poisonous from non-poisonous except by correct identification as the genus and species
There is no easy control for lawn mushrooms, which appear whenever there is an extended rainy period. These mushrooms grow in organic matter (including thatch) and decaying wood. Where possible, the removal of buried wooden scraps and old stumps will greatly reduce their food source and the number of mushrooms in future years. Mushrooms that do appear can be raked up and destroyed, minimizing danger to children or pets.