Nutsedge is notoriously tough to control but there is a spray that is made specifically to kill it. We sell it at Hewitts.  It is called Hi-Yield Nutsedge and Horsetail control.  We also sell the “spreader/sticker” they suggest adding to the spray to help it stick to the foliage of the nutsedge to help it get absorbed better.  HERE’S a link to the product for more information .