That does look like poa triv. Pre emergents will not do anything to triv, they spread via stolon and don't seed like poa annua..pre-m will work against poa annua, but not triv which you may have. Even tenacity may whiten it, but won't kill it. Triv can even come back from roundup/glyphosate. The only full proof ways to take it out are dig it out(but don't leave any stolons!!!) or use certainty herbicide which is known to work on triv. Certainty can kill tall fescue though if you have some in there. I did 3 round of glyphosate on my triv last fall when I was renovating and much of it came back this year. I have TTTF so can't use certainty. Triv is the devil.....

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

I try and avoid using roundup unless it's a last resort, and/or lawn renovation; Because of the varying degrees of the half life of Glyphosate. Phosphorous levels have a profound effect on the degradation of Glyphosate. For example, Low Phosphorous contents of European soils decreased the degradation of Glyphosate (Laitinen et al., 2006; 2008; Borggaard and Gimsing, 2008). Another study (Laitinen et al., 2009) showed undecomposed Glyphosate, about 19%, as well as APMA (48%) 20 months after application. Overall, Glyphosate has varying degree of half-lives that depends on numerous things. (de Jonge et al., 2001; Gimsing et al., 2004a, 2004b; Mamy et al., 2005; Sørensen et al., 2006; Gimsing et al., 2007).

Other than herbicides it sounds like good cultural practices can lower the pressure of trivialis. Triv is very suceptible to disease, so instead of applying a fungicide let the disease take the weak. Triv has a small root structure and spreads by stolons so grow the surrounding turf thick to fight against the stolons. Also heat stress will limit it's growth but unfortunately it's a perennial. Since it spreads by stolons aeration might have to wait. The broken pieces of the stolon could spread by the machine to other areas of the lawn or be brought from other lawns.