Use the Teancity at seeding time as per the directions. It starts working right away and last 30 days I think. That gives your seed an advantage. I think you may be reading the post-emergent direction also. The new seeding instruction I have in front of me clearly say not to reapply until after 2nd mowing or 30 days (whichever is longer).

If you have existing weeds you want to get rid of before seeding, use gylphosate (Roundup). You can spot spray particular weeds. Glyphosate kills grass too so there will be collateral damage, but if you're seeding, the seed will fill in the dead spots. You can use glyphosate and seed soon after (be sure to use the regular kind, not extended control). Tenacity is a specialty herbicide. It can be used as a short-lived pre-emergent at seeding time. It must be mixed and applied precisely as possible and you are limited on how much you can use in a year. Do more reading on it.

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!

Here are some questions and answers on Tenacity. What is more important to you: killing the weeds or seeding? You could do the Tenacity treatments every two-three weeks and put off seeding (perhaps do dormant seeding in winter) or you could seed with just one Tenacity treatment now at the time of seeding. It may not be enough to kill the weeds. Maybe call the manufacturer, 866-796-4368, and ask for their recommendation.

Use becky's 2nd suggestion. Use it now for seeding and spray everything, protecting your seedlings and killing the weeds. In 30 days, as instructed on the label, you can repeat the application.

That's 30 days after germination, not 30 days after seeding. Or after two mowings (of the new grass).

If the areas you want to seed and want to kill weeds are distinct areas, you can treat them separately. For the weedy areas, follow up with Tenacity after two to three weeks (seedlings may be harmed). For the seeded, non weedy areas, hold off on additional Tenacity until after the second mowing or 30 days after germination.

Thanks both!!

yes, you should have killed the bad grass with T mid-August. but you can follow becky's advice but you may not fully eradicate the grasses. I know, I missed the timing also :-(

Start blanket spraying every 5-7 days for 4 weeks or so. You will kill new weeds that germinated with your grass and also existing bentgrass.

Hi mishmosh - thanks. I've got grass germinating now so I'll assume you mean wait a few more weeks before I start spraying as any spray right now will probably kill my seedlings.

Again I'm no so worried about new weeds growing right now - that's minimal.