Poa Annua actually begins germinating once soil temperatures dip below 70F and continue falling. It's there all Fall, but is small and not noticeable. It winters over, and fires up before many grasses do in Spring. By the time your lawn wakes up, it is almost at the seeding stage. With the summers heat, most cultivars die off, and the cycle starts again in the very late summer.

So 1st week of September in Northern NJ sounds about right? What I'd really like to learn is the science of how pre-emergents work.

Pre-emergents work by prohibiting germination. For example, Scotts Halts will last 4 months so applying in the fall will not work for controlling spring weeds unless you apply again in early spring. I can't speak to the life of others however. I know tenacity is a great product, but not sure how long it lasts.

Most people will apply in the early spring to prevent crabgrass from germinating and then apply again in the fall in order to prevent poa annua from germinating.

I'm in a situation where I want to prevent the poa annua, but need to overseed as well so I'm not sure what to do myself.

Watering doesn't normally play a role in when to apply.

Tenacity lasts about a month, and doesn't inhibit grass seed. But it does inhibit P. annua, so it's a great choice for seeding time with P. annua problems.

So Tenacity would be a safe bet for a pre-emergent if I want to overseed this fall and spring after aerating?

How would you suggest doing all the above? Tenactiy on 8-1, aerate and overseed on 9-1? Or would I not have to wait that long?

Can I get Tenacity locally? Is it applied like a fertilizer?

Aeration is an entirely separate question, to which my general answer is, "Don't do that." Ditto with spring seedings, which aren't terribly effective.

You can apply Tenacity and seed the same day or any time thereafter. Off the cuff, most Zone 6A regions have their proper fall seeding time around mid August, but it does vary.

You can get Tenacity at most Lesco stores, and most recently I'm starting to see it in big box stores as well here and there.

It's a liquid, so you'll end up using a hose-end sprayer to apply it. Or backpack sprayer if you prefer.

Morpheus, I do have a background in turf management so I know I have a thatch issue where dethatching has not worked and am only aware of aerating as the other option. Previous owners laid sod and never watered or did any type of maintenance. If you know of a better solution, please let me know. I've read, and seen a lot about homemade dethatching concoctions, but am not buying in yet.

I dethatched 2 weeks ago, and pulled up 6, 30 gallon bags worth of thatch in a 1400 sq ft area, while using the highest setting.

NJ, I've found it on Amazon but I have not found any local place that carries it, big box, specialty or co-ops.

Try some consistent high-protein organic feedings. I've got pure elite KBG, the second-thatchiest grass behind Zoysia, and have absolutely no thatch. Nor have I for years.

If dethatching isn't working on your thatch, something else is going on. By definition, that's what dethatching does. If what you mean is that it rapidly builds up again, then I'd check feeding and watering methods followed very closely by evaluating the soil's chemical and biological health with a Logan Labs basic soil test.

My kids play too often in the backyard. I want to put a granular down just before a rain storm and then not have to worry about it too much. Just like I did with the Grub Ex this past Saturday. We got two inches of rain between Sunday and today and my the time we dry out tomorrow after school I have no issues with the kids going on the lawn.

To my knowledge, nobody has Tenacity in granular (yet).

Tupersan is your best bet in that case. The number of weeds it stops is rather small, and mostly broadleafs, but even that can be a help.

Why would I not use just Johnathon Green's Crabgrass Preventer with Green Up. It says on the label it is used in the Fall as a pre-emergent for Poa Annua.

This is what happens when we have somebody seeding and somebody not seeding in the same thread. He's limited to Tenacity or Tupersan. You can use whatever you like if you're not seeding in fall.

"To my knowledge, nobody has Tenacity in granular (yet)."

Pure Tenacity? No. But the Scott's product "Starter Food for New Grass Plus Weed Preventer" (granular) contains Mesotrione as the active ingredient as the weed preventer. Mesotrione is the active ingredient in Tenacity. It works equally well as Tenacity as a pre-m, but not as well as the foliar-applied Tenacity as a post-emergent.

If you are worried about toxicity, Tenacity was quickly approved by the EPA as a "Low/Reduced Risk" product - it is the synthesized copy of a natural Bottlebrush substance. It is much less toxic than other herbicides.

Sorry to derail this thread everyone.

NJ, hope you figured out the route you are going.

NP, let's keep the discussion rolling. Lots of good info here so far. If I were to overseed bare spots in the Fall and still want to use my JG pre-emergent on the entire lawn for the Poa Annua prevention, what would the timing have to be?

You'd have to check the bag; most pre-emergents have various rates for various lengths of coverage. For fall overseeding, you'd want to make sure the shield drops no later than July.

If fall seeding, or a full reno, is on the table, I tend to recommend skipping the spring application of pre-emergent. A dry summer will slow the degradation of the pre-emergent layer and may lead to problems when seeding. Plus most companies seem to underestimate the time the shield will be up.

I apply a nine month shield of Prodiamine to my stone deck and my mother's, and it's effective for more than a year. There will still be some weed suppression next summer from what I did this spring--although I'll renew it next spring anyway unless I forget.

If you have areas that you know you would like to overseed on Pre-M drop day - you could always layout tarps, cardboard, or similar to create a shield in those spots. then you can apply Tenacity with sprayer to those areas on occasion to maintain a barrier (30day intervals approx, iirc)

NJ, I can't speak for the product you want to use but I know it has been suggested to put down Tenacity before you overseed. This way the seed has the upperhand on weeds. I would assume the same logic would apply to your product, but I would definitely check they label. You know what they say about assuming...