That looks like it. And a LOT of it. Sometimes you can see ripples in the leaves, just like poa annua. I've noticed some starting to seed in my yard right now unfortunately. Seedheads look a little different than poa annua or KBG.

Any recommendations on getting rid of it? Round up? What time of year, etc?

If it's in the lawn, dont use roundup or youll have big brown spots all year. Use a selective herbicide if you can, or just pull them

Trust me...I understand what Round Up will do. Researching others expierences, it seems like there is little to no selective herbicide that will control Triv effectively. The area is large enough that just pulling it is not feasible.

I just tried some Tenacity on Sunday. Some report that multiple hits will take it out. I'll let you know.

Is it just part of the lawn that you have this? If that area is wet AND shady, it is a losing battle. If not, I'd try Tenacity at 2oz/A application rate every 5 days for 6 weeks and see what that does. At least it can hold it back from further spread or outcompeting desirable turfgrass. You may find though that some areas may be completely poa triv when you get bleaching from Tenacity. If that is the case, I'd just round those areas up and reseed in the fall. Bear in mind that war using Tenacity will not leave you with a good looking lawn while you are using it.

Its not very tolerant of dry conditions..... so you can let the area dry out brown ( if the weather will permit ) the poa will die , but the KBG will come back when water returns. Make sure you remove any seed heads that form on the poa ( by mowing and bagging) The poa will make seed heads when the plant is water stressed.

So I take it that killing it with round up and reseeding in the fall will likely fail because of the area being shaded and moist during spring?

most desirable cool season grasses do not like wet and shady conditions. ultimately the conditions will dictate what will grow. you cannot will grass x to grow where the conditions dont favor it over species that love those conditions... at least when no selective herbicides can tip the scales for you.

i have an area of wet and shady. i have tried everything. my final solution was to nuke it and sow improved poa triv and white clover. i do not ferilize that area and simply mow it at 3". i dont recommend it to others but it works for me for that particular area of my backyard of approximately 1000 sq ft.