Answer: Obviously some tree roots remained. There is nothing you can do to kill the suckers without killing your lawn so the best control option is to mow you lawn and mow down the suckers as they are just beginning to emerge. Each time the root sends up a sucker, it uses up some stored energy. If the suckers are not allowed to develop leaves to replenish the energy, the roots will eventually run out of energy and die. You just have to keep mowing them down before they develop leaves. An alternative would be to cut the sucker off and then paint Round Up or other vegetation killer directly on the stub. Of course Round Up will kill your St. Augustine, too, you you need to apply it very carefully and only to the stub of the sucker. Good luck with your lawn!
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