Here are two pictures of but one of the nutsedge varieties found in Florida. Not sure just which variety this is, but it has these thick, strong underground traveling root networks. The ones here had been hit with RoundUp once per month for the past six months. As you can see, it did not really kill them after all.

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This is how I am dealing with this menace. I am digging down to 18 inch depths and beyond, but I am getting the beasties out, root, nut and all. Thank goodness that I have sandy soil, for if this were real dirt, the work would kill me.

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Some poisons kill some varieties, but anything strong enough to eliminate nutsedge will be strong enough to kill everything else.The only cure I know is called digging. You either kill all living things with herbicides or you kill your back from digging. For now, I dig. For now.