Unfortunately, Poa annual or triv. isn't classified as a weed, but as a grass. So even if a bag of seed list 0% weed seed, if it has any percentage of "other" listed, it very well could be poa.

I bet thats it ! Dang. The fescue came up better than any seed I've ever purchased so part of me thinks its worth it, but I don't know. Does it spread like a weed? Or does it kind of stay put like a real grass ?

Also found this on google.... i wonder if this is it: "It is rather difficult to control because the plant will produce several hundred seeds in one season, and the seeds can lay dormant for several years before sprouting."

Tenacity will kill it but it takes some time and your lawn will have bleached spots for a month or so. If it hasn't started producing seed heads yet I would definitely give the tenacity a go. Once it starts producing seeds things go downhill really quick. The plant itself doesn't spread per se but if left untreated you can expect at least twice as much next year due to the heavy seed production. It will take a good preemergent program along with Tenacity treatments for several years to completely get rid of it.

I'm going to disagree just a bit with forsheems. A good pre-emergent will take care of it in a few seasons. I am a Bermuda person so I don't know how fast it will fill in if killing it. I would say to let it be and attack it hard with a present emergent in the fall and next spring. Only thing is hopefully you don't reared it again.