Mushrooms are a common fungus found growing in lawns. While very few mushrooms harm the grass, they are unsightly; some mushrooms, which are also called toadstools, are poisonous. Unfortunately, no chemicals are registered to treat or kill mushrooms, therefore, other control methods are in order, including removing thatch and mowing frequently. You can also use both dish and washing powder to treat and kill mushrooms found growing in your lawn.
Mix 1 to 2 tbsp of dishwashing detergent for every 3 gallons of water. If you have a hose end sprayer, use 1 cup of liquid dishwashing detergent for every 20 gallons of water sprayed.
Walk on the area where the mushrooms are growing with aerating sandals. Or, poke 6-inch holes about 12 inches apart in the area where the mushrooms are growing. A screwdriver works well.
Spray the area with the detergent and water mixture, applying about 1 to 2 quarts for every square foot.
Sprinkle the tops of the mushrooms with dry, powdered washing powder. Use enough only to cover the mushrooms with a light dusting.