Where do you live?

I can't see any difference in the pictures. It all looks good. Can you take the pictures on a cloudy day or when the sun is not shining directly on the grasses? And don't use the flash if you're in the shade. Natural light is best.

Is the intruder a coarse bladed grass or fine bladed?

How high/low are you mowing and how often?

I'm in Bastrop (30miles outside of Austin). I can try and take some pictures tomorrow morning once I get home from work.

The intruder grass is more coarse than the 419 is, not St. Aug coarse but noticeably coarser than the 419. It's runners are super long and taking off like crazy. I've compare it to runners from the known 419 around the yard and they just don't compare. The intruder grass feels completely different than the 419.

I've been mowing once a week about 3", cant mow any lower due to uneven spots around the yard at this moment that gets scalped.

Just a slight distinction that Bastrop is 30 miles east of Austin. It makes a difference whether you are east or west of I-35 and you are well east of it. I-35 was built on a dividing line in Texas, so you're east of the Hill Country in an area where just about everything will grow.

One grass that is more aggressive than St Aug is kikuyu grass. I would not expect to see it in Bastrop, but if someone imported it, then it's possible. There are some relatively fine bladed varieties of St Augustine. Are the tips of the blades blunted (St Aug) or pointy (anything but St Aug)?

Have you considered leveling the surface? Basically you would scalp it as low as possible, dump sand on it, and drag the sand around with a drag (like they use on baseball infields) to fill the holes. This is a DIY project that really pays off. People report going from what you have to a putting green surface in one weekend. Of course it takes a couple weeks for the grass to grow back, but they really like the new flatness of the lawn.

That's kind of what I had originally thought this grass was, a fine bladed St. Augustine but wasn't sure if there was such a thing.

Before I dug up the excessive dirt from my drainage ditch there was grass growing in the ditch but wasn't sure what it was. This unknown grass is most likely that. The tips are some what pointed but I did notice yesterday that a lot of tips had that "chopped" looked that St. Augustine has after mowing.

I went ahead last night and put down a weed/grass killer on the unknown grass with plans to lay SOD next weekish. I'd rather get ahead of this before it spreads too far.

Yes, I have considered leveling and it is up there on my "to-do" list and something that I want to do. I just need to get the rest of my yard some grass then I'll probably start leveling the front yard.

Jake,

Yes coastal bermuda was another possible culprit that my co-worker suggested. I do believe it came from the grass that was growing in the ditch.

Make sure you don't bury any of that torpedo under the new sod. You'll never get rid of it if you let it root under the new 419.

Hopefully it will all be dead by then, if not I'll make sure it is. Going to check back on the grass in a few days and see if I need to respray the grass killer anywhere.