Agree. Don't waste your time pulling them up. They have very fragile root system with a bulbous, nut-like, growth down a few inches. The roots easily break off from the nut leaving the nut in the ground from which you'll get 10 more spawn. Just spot spray the ones you have and keep after it. These are sedge plants, so be sure you get the right spray. Grass or weed killers will not work. It has to be a sedge killer. How have you been watering? Nutgrass usually grows best in soggy soil. I have gotten rid of it simply by changing to deep and infrequent watering. If you are already watering deeply and infrequently then you might have green kyllinga. Green kyllinga is another sedge that looks like nutgrass but has a different seed head. It is much less aggressive than nutgrass and lives just fine in very dry soil. It is also a sedge and must be killed with a sedge killer.

poa trivialis and the last one poa annua

Thanks lawniac. Well I won't say it's easy by Google. As clean, close up pictures are rare. And I see same picture labeled as different grass at different sites. So not accurate to say the least. For instance I'm trying to identify following two grasses Both I guess same species of different variety. one is short leaves other has long leaves. one is denser than other and little lighter in color. I failed to find any picture on google that is properly labeled with the grass name and positively matches either of these pictures.

Your zone means nothing, especially since it is not in the USDA format for zones. Even if it was it is meaningless for identifying grasses. The USDA zones are used only for identifying cold hardy plants. What we really need is the name of your city or community. Identifying it as the southeast is helpful, but in my mind, that is a region from North Carolina to Miami to New Orleans and includes Tennessee. So it will really help if you can tell us where you really live. Having said that, the grass looks like either St Augustine or centipede. Since it was recently mowed, all the tips have been clipped off. You cannot readily see the difference between those two grasses unless you can see the blade tips. St Augustine is blunt at the tip and centipede comes to a point as shown in this picture.