Also called Rough Grass
Since this is one of the bluegrasses, it always has a boat or canoe like shaped tip. This is the first thing to do in terms of identifying Poa annua and/or Poa trivialis.
I have been watching this clump of Poa trivialis in my front lawn for several years. It spreads each season and I decided I needed to figure out what it was so I could control it. I knew it was a type of bluegrass, and knew it was not Poa annua. I sure would not want this taking over my yard and I understand that in more northern areas it is very common weed.
Below is a close up of Poa Trivialis
The pen in the center is to measure the height.
The blue pen was stuck down in the middle for purposes of seeing how tall the grass was. The grass is 8 inches in height which much taller than Poa Annua. The photo was taken on December 10, 2015 and it had been several weeks since the last mowing.
I have been watching this clump of grasses for about three years and it is steadily spreading. As you might have noted from above it is commonly called Rough Grass. Strange name it seems to me because the blades are not rough at all. The rough refers to the fact that it spreads with rhizomes which are right at the surface of the soil. In our local lawns this grass does not usually develop seeds because it is mowed too short to produce seed heads (not like Poa annum.
Poa trivialis is a cool season grass and does not like the heat that we get in the summer. During hot weather it will die back but come back again in the cooler fall and winter. If this grass takes hold, it can be extremely difficult to remove. It will spread by seed so if it gets into a rough area which is not mowed, it can spread from there. Even roundup does not do a good job or controlling it (so I read) but repeated treatment can control it. Meanwhile have grass tall enough and growing well in fertile soil will tend to choke it out. In this case I plan to spray this grass with roundup now (mid December) and reseed with fescue. From past experience I know that fescue will germinate when we get some warm weather. Usually by mid February, we will get a week of warm weather and that might be all it takes to get the grass growing. We observed this over many years when we removed a stump and put fresh dirt in the hole. Scattering seed germinated surprisingly quickly.
As the season progresses, I will post here what I am finding. I plan to spray part of it with roundup and dig up another chunk.