Thanks so much for the comments hawksster and becky. Just a bit more to clarify my original post. I have done reading on T and I understand what it is, and I realize there are multiple uses, namely post and pre-emergent. What's happening in my case is, I guess I'm looking to use as a post-emergent to kill existing bentgrass, perhaps barnyard or orchardgrass, etc. - BUT I find myself attempting to use as post-emergent at the same time as planting new seed. I'm really not using as pre-emergent as I won't have a problem with weeds growing among my new grass this time of year. As an example, in many areas where I have bentgrass, it is mixed in with very healthy KBG/rye/fescue mix. I don't want to kill the desirable blend in these areas as they have a good deep root system and survived the drought well. Killing this area with glyphosate doesn't make sense - it defeats the whole purpose of using Tenacity (selectively killing the undesirable bentgrass...) But I think I'm realizing I missed the boat - I should have applied T as post-emergent a few weeks ago in August, and started the killing process then such that I could grow new grass now. I was just posting this predicament in hopes I might be missing something or a trick of the trade... Thanks!

I say apply prodiamine as usual and deals with existing weeds by spot spraying. There shouldn't be any crabgrass yet, it's been warm but not that warm. Once you get a crabgrass free stand of grass you will find your next biggest problems to be Bermuda and fungus, both far more formidable opponents than crabgrass.

Tenacity likely will take more than one spray to kill the crabgrass. But it will “light it up” so maybe the next time(s) you can just spot spray. Also you don’t have to wait between Tenacity application and overseeding. Scott’s Starter Fertilizer with Weed Preventer actually contains the active ingredient in Tenacity. So you don’t have to wait until 9/21.

It'll come back. I've hit it with a ton of Tenacity. It seems dead but new sprouts come out when the Tenacity applications end. Even on a blank canvas of a new seeding, triv has no problem sprouting--maybe less but who really knows. I had wanted to try Velocity but seems it is no longer made and the ag equivalents are super expensive. I still try to hit it with Tenacity very early spring and avoid irrigation in the summer to let the lawn go dormant. Has kept it in check.