Answer: I'm afraid the roots will continue to sprout as long as they have stored energy. Typically when a stump is ground it is also given a dose of chemical stump killer (such as glyphosate) which is translocated into all the roots and will usually kill them. It needs to be applied when the tree is first cut down and the vascular system is working. Now that the stump has been ground, the underground roots are attempting to renew its stored energy by putting out sprouts. Once these suckers develop leaves, photosynthesis takes place and the roots get their energy from the sun. You can eventually starve these roots out by keeping the shoots cut off at ground level. Depending upon how extensive the root system is, this can take several years. At this point there is nothing chemical you can use to kill the roots that won't also kill your lawn. You can dig out the roots to keep them from sprouting or you can continually cut the shoots and suckers that appear, or you can cut and roll your sod (to protect it) and then dig down to the roots, drill holes in them and then apply a vegetation killer (Round Up or Brush B Gon). You can reroll your sod once you've treated the roots. Wish I had a better solution for you!
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