Answer: Mushrooms are growing because something underground is decomposing. Could be tree roots, could be mulch material or other debris, but as long as it is decomposing, mushrooms will grow. You can simply knock down the mushroom when you see them or you can dig down to see what is causing them to grow. In any event, don't spray Round Up on them. It won't kill the mushrooms but it could kill any other plant it touches and it could harm the tree roots.
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