We have lots of nutsedge/nutgrass around here. It pops up whenever the rest of the grass is heat-stressed. Sometimes, I hate to kill it because its the only green stuff in the lawn. We have several options of weed killer that targets it. The one I use now is called Image - active ingredient ammonium salt of magnesia. But if you go to a nursery instead a big box, there are a lot more options.

I remember the guy who used to do a lawn/garden show on HGTV say he stopped thinking of his yard as a lawn and preferred to think of it as a meadow, where diversity is an asset.