Round Up is a good weed control with minimal environmental issues. If not over-applied, it kills the weed and root, but NOT the nut. Sedge Hammer is slower acting than Round Up but kills the nut along with the weed and root. The reason nut grass is so hard to control is that the nut is difficult to kill and keeps sending up new shoots. We can only kill the nut through this new growth. The active ingredient of Round Up translocates through the photosynthesis process from the leaf and kills the root. The active ingredient of Sedge Hammer translocates through the photosynthesis process and kills the nut AND the root. The hard part is getting to all the nuts because the green leafy part is not emerged all the time.
If we try to kill the Nut Grass with Round Up we do not kill the nut, which is bad enough, but we are also killing off that new growth that is needed to translocate the active Sedge Hammer ingredients to the nut. This will allow the roots and nuts to thrive and spread underground.
Even over-spraying Sedge Hammer or Round Up by themselves can be counterproductive. You could still be killing off the leafy part before the active ingredient can translocate to the root and/or nut.
Also be careful about removing the dead Nut Grass too early. It may be unsightly but the active ingredient needs to go through percolate down. (This is applicable to other weeds also, but Nutgrass takes longer). Usually if the leaf is dead from the spray (if not over applied) the root has died or is dying.
Note: Garden View not a Licensed Pest Control Adviser. Always read all the instructions before applying any pest or weed control products. The above information is not instructions but intended as aid in understanding how the products work.