With most herbicides, it's far safer to wait until the third mow on the youngest grass (or, if you don't get to that point, until spring when it's definitely hardened off).

While Tenacity is one of those herbicides where you're more likely to get away with pushing it, I still wouldn't recommend it at this point. Your weed problem doesn't seem that bad from the closeup (that's pretty normal). Annual weeds won't survive winter (like crabgrass, which is probably already gone or dying). Perennial weeds will, but spring is time enough to take care of them as they tend not to be active over winter.

Thanks for the reply.

Crab grass is certainly not a problem right now as I killed off everything about 2 months ago, weeds and good grass alike. But Ill tend to crabgrass maintenance in the spring. My biggest concern is controlling the poa annua if possible. Im sure at this time its probably germinated? Though I haven't examined closely, but this is the time it would to the best of my understanding. Will tenacity only work on poa annua as a pre-em or post as well?

P. annua, if it hasn't already sprouted, will do it very shortly--the clock is rapidly running out even in Zone 7!

Tenacity does work as a post-emergent for P. annua, but several applications may be required to kill it or control it. I tend to have very good luck in my lawn with Tenacity, and two or three shots of the stuff separated by 2 weeks each on any young P. annua patches will take them out.

I have really soft water, though, and that seems to help. I might recommend mixing your Tenacity using the cheapest single-distilled water from your grocery store and spot treating P. annua if you're using it as a post-emergent. There's no need to spend for better water than that, the most basic distillation is sufficient--and add a non-ionic surfactant at bottle rate, like Bonide's Turbo Spreader Sticker.

Most other controlled weeds don't seem to care and even very hard water is fine.

The weed looks like henbit, which is a winter annual (sprouting in fall, growing in n spring, dying in summer). I have a similar dilemma to yours. I overseeded and have a lot of new grass. I used Tenacity at seeding (4 oz /acre rate) and did a second application around 5 weeks at the 2 oz/acre rate. My initial plan was to do two follow-up applications and then use prodiamine as a more effective pre-emergent in November (trying to ward off poa annua). I haven't done the second follow-up and don't think I will and I think I'm going to wait until March for the pre-emergent. I will save the Tenacity for spring when I can identify poa annua (if I have it now I don't recognize it) and use spot sprays (mixed at 2 oz/acre rate) then. Reason for change of plans: all herbicides are a stress and I want the new grass to grow as well as it can now before the season shuts down. I can deal with weeds later. Some of my new grass has been slow to come in. I wonder if the Tenacity hindered germination and growth of some of the fescue. I put more seed down at the same time as the follow-up application of Tenacity because some areas were very thin. They are still somewhat thin. I never had this problem with other overseeding and this is the first time I've used Tenacity.