Unfortunately it looks like you have some poa trivialis growing in your nice turf. There are a few other grassy weeds it could be as well. Triv is a notoriously hard weed to get rid of, it can even survive round-up. If you have the time, you can hand pluck as much as possible, making sure to get as much as you can. You can also remove the entire top layer of turf, fill in the hole, and let your good grass spread into the area, but that's only if you have KBG, or another type of spreading grass. I believe the herbicide Certainty can be of help, but being in Canada it's probably not an option, and applying it can hurt the rest of your lawn. I have had some success using weekly apps of 2,4 D and Triclopyr to poa triv, but it came back this spring.

If you wanted to kill the entire lawn, rid it of POA Triv, and use sod, what is the best way to assure it's gone? Would repeat roundup applications over the course of 4-6 weeks be enough or do you really have to remove 2 inches of turf? I have killed it with one application of roundup in the fall, only to have it come back stronger in the spring.

Certainty and Tenacity is mentioned around here a lot

Soil sterilization would ensure that your soil is free of weeds, and weed seeds. This can be done with steam, chemicals, or via solar sterilization. Steam is very safe, and reasonably quick, but it requires special equipment. Solarization you can do yourself, but it requires your yard being covered in plastic sheeting for a month or more. Most chemicals used for sterilization are highly regulated, and aren't available to homeowners. The issue with Round-Up is that when you apply it in late summer most poa triv is dormant as it doesn't do well in heat and full sun. When you seed and start the daily waterings the weather is usually cooling down, the perfect environment for triv to return.

What do you think about hitting the entire lawn with roundup from September through Mid October and then SOD early November. Will it be active in September? Or nuke it right now and live with a dead lawn for three months.

Poa triv will certainly be more active in late summer/early fall than in mid summer, but there are no guarantees with triv. In theory it should work, and also putting sod on top of it should give you a leg up on any remaining stolons, but again, it's tough stuff.

Here's a very informative page about Poa trivialis, a.k.a. Rough Bluegrass, that may be useful to you. It includes tips on how to get rid of it:

http://www.american-lawns.com/grasses/bluegrass_rgh.html

Hello,

Would you guys even say I have Poa in the first image? This stuff seems hard to get rid of. Just last summer in the front yard (first pictures) my wife and I thatched and re-seeded... Could the poa have come from the kbg mix from Scott's that we bought?

I always thought it was annual POA, but it evidently is trivialis. I have no idea what it is, don't really care as I don't want it. I have had it in my lawn and nothing I've put on it phases it (haven't used roundup). It is very easy to pull up though. I've had good results in pulling it up and reseeding with a divot mix of KBG. Always doing another spot as the neighbors lawn is full of it.

The lAwn looked good in the first pic. I never thought of canada as a good place for nice grass

rmj619: LOL Canada is pretty awesome. You'd be surprised!

Canada's a great place. I look forward to seeing your Canadian band Rush when they come to St. Louis in September. I've never been particularly fond of the group's name "Rush"--kinda sounds a bit druggy to me--but those guys rock! As a kid, I learned all the lyrics to their album "2112". Thank you Canada for producing Rush and all your other great musical groups, and for the many, many other great things you do!--which can't all be enumerated here in this forum devoted to grass. You do so much so well :-)

I just recently came to the conclusion that I have the same problem in my lawn... I had initially misidentified it as yellow nutsedge so I tried some ortho nutsedge killer on a small spot. Within a day or two, the poa died off. Do you think this is a good treatment for it? I was considering spraying all the spots ... Maybe digging up a little and putting down new topsoil and reseeding. Does that sound like a good plan? How soon can you reseed after the nutsedge killer?

Thanks.