Mushrooms usually occur in lawns after prolonged periods of wet weather. This often indicates the presence of decaying organic matter in the soil such as old tree roots, stumps or construction debris. Most mushrooms cause no damage to lawns and they will disappear when the weather conditions and soil dry out. If they grow in circles of dark grass called “fairy rings”, they may injure the turf by making it impervious to water. There is no effective chemical control for mushrooms. However, if you feel they are poisonous or unsightly, simply remove them with a rake.