All you can do if these sprouts are coming from the roots is mow them or dig them out, maybe including a section of the root as well. However, digging them out will just encourage the tree to do it more. There is a sprout inhibitor chemical you can apply called Tre-Hold, but I'm not sure it works very well. Also I don't know what it would do to grass. I am sure you would have to apply it every year. Most trees don't sprout from their roots, so another alternative is to plant different trees.