It looks like you may have the same two annual grasses that get in my lawn this time of year. I am not positive of the ID, but one is very low growing with little white seed heads that I'm pretty sure is Poa annua 'annual blue grass'. The other I think may be annual ryegrass.

After they sprout the only way I know to kill them is pulling them. Sometimes I have to use a digging fork to loosen the roots. The most important thing is to get them out before they produce seed from which next year's crop will sprout.

You may be able to prevent them next year by applying pre-emergent granules in the fall at the proper time for your locality.

Yes, it's work, but getting them out becomes a rather pleasant obsession making the efforts a little easier. I wish you well.

I was thinking it was poa when I saw the seed head too. Thank you! What a stubborn grass. Looks like I have some pulling to do.

It‘s def poa annua. While your lawn is still domant, you can spray them with 20% vinegar. That will kill the foliage. If they’ve already produced seeds, be sure to apply a pre-emergent in early fall.