I survived 3,000 sq ft of it last year. You're describing Poa T perfectly - you only missed one characteristic: it likes to "lay down" as the season progresses. It doesn't need to be underground to spread - stolon cuttings will do just fine in the right conditions. The pictures definiely look like Triv.

Tenacity can help here, and it doesn't kill your (northern, which I assume it is) lawn. Although several sprays may be necessary to finally control it, and you do have to keep after it (it'll keep coming back for a number of years), eventually you do finally get rid of the stuff.

No, it's not triangular. It's more like a little flatter and taller than the boat shape kbg. I asked the lady at the nursery if it's anything to worry. She said it's probably just new grass that was mixed in with the seed. But what kind of kentucky bluegrass would look this bright green? I've patched up partial renovation on another part of my lawn and it came in much darker than that and did not sprout that fast. The bag I used had some wildhorse kbg, would that be a bright green at first and eventually turn darker as it matures? I attached another picture, and I will pull some out from the root and get a closer shot. Its actually in a few other places in the lawn in very small patches. I really don't know. The only reason I was inquiring was because my lawn is finally an okay looking lawn. It's uniform, no big dead spots or anything, some weeds, this is the worst spot of my lawn behind the tree. I just don't want this patch taking over half the lawn. It seems to have spread fast. The pictures really do not show the true lawn. The color looks very washed out. The lawn looks much darker green 95% of it with a slight blue hue, and that bright spot looks brighter green in person. Should I maybe spray this with a selective herbicide and see what happens? It's sort of hidden behind the tree, so even if it kills it, I could always try a late reseed of more kgb in that whole spot. This post was edited by ligrass on Sun, Sep 22, 13 at 20:26

Despite what I'm being told I am pretty much giving up hope that all these seed heads are coming from my turfgrass. I've been researching poa annua a little bit more and images I see online look very much like what I have going on in my lawn. Here are a few more pictures of my lawn... Opinions? If it is poa annua (I'm convinced that it is), I can't for the life of me figure out why this is happening. My lawn was started from seed in September 2013. I didn't have any poa annua problems in 2014 (nor any of these seed heads). I mow high and I water infrequently. And the kicker is I see nothing like this in any of my neighbors lawns, none of whom take lawncare seriously...so why would it take hold in my thick, high lawn but not in theirs? Was it mixed into the seed the landscaper used but didn't take hold until now? I overseeded last Sept but I know it wasn't in that seed because I had a few bare spots I fixed and those spots are free of these seed heads. And what do I do about it? Kill everything and restart? Keep spraying Tenacity in hopes I beat it? Or, since it's an annual, will it all die this summer, then use preemergents more aggressively?