Eastern PA here. I get/got both triv and annua, and beat both back with Tenacity (in a bluegrass lawn). It's not a once-and-done prospect, and you do have to get the timing right, and you do have to keep after it, but if you do, you can overcome the issues.

And you do have to combine the Tenacity with a pre-emergent like Prodiamine to keep the stuff from seeding out like mad (more annua than triv, although triv will do it as well).

With triv, I find it most helpful to hit it with Tenacity in summer to weaken it just before the worst of the heat hits (such as one gets in PA where it does get hot but we're kind of temperate rainforest). Then strike it before winter so it's weakened for both seasons.

Eventually it does give up the ghost.

If you spray once and expect it to go away? Naw, it'll laugh at you. Or if you time it right before a good growth season, it can recover pretty easily. Do it when the stresses are about to mount up.

And yeah, triv is just evil. It'll take some years to abolish it and your neighbors are going to be sources for years to come. In the meantime, strengthen your main lawn to help fight the problem. Get the soil tested. Water deeply and infrequently when it needs it. Feed at the right times (very late spring and fall). Keep that pre-emergent layer down in fall when P. triv and P. annua sprout. You know the drill.

As always, thank you, Morpheus for your insight and even more importantly, your encouragement. I still have hope.

I've had the pleasure of using Tenacity before on various undesirables so I'm at least familiar with the process. I do not expect at all this is a one and done treatment and I'm ready for the long-haul battle. (btw I also have some poa annua in decent proximity to the Triv. This is all in my backyard, which I would characterize as plenty of morning shade with some midday sun, not too brutal in the late afternoon/evening. The front yard BAKES in sun starting late morning onward all day so I'm expecting won't develop Triv/Annua issues.)

So then, a few questions on my Triv:

So with our drought and heat conditions so far, the Triv is suffering right now. I'm guessing I should have hit it with Tenacity while still thriving, but just before this weakened state. AKA I should NOT hit it with T right now while it's suffering, correct? In other words, is there anything I should expect to do for the rest of this season in terms of even beginning to control? Perhaps based on above I should wait now but hit it before winter. And hit it once? twice?

Perhaps for the rest of this season it's using the Prodiamine. I will educate myself on that one - not familiar. and btw, I take it then that Tenacity is not an effective pre-em for Triv (and Annua, for that matter?). Related to this then, when should I put down the Prodiamine? I think Annua germinates in the fall around these parts. I want to say Oct/Nov? What about Triv?

(I once came across a bag of Scott's Halts and tried putting that down in Sept to prevent Annua - not sure it really worked but I could have missed the timing of it).

Back to the Triv and the rest of this season: if not attempting to control this season, then does this mean I should wait until next spring? When would you suggest I start that exactly? A few weeks before the heat/drought of the summer? Hit it with T once or twice BEFORE the heat weakening? And then what? Hit more after in late summer or I think you're suggesting wait until just before winter? Should I expect to dig up old/dead Triv to remove stolons? Reseed in fall with my desirable mix? Does that mix germinate through the Prodiamine?

Also any particular rate on the Tenacity I should use or just stick with the usual recommended for residential lawns?

Now you got me goin' :)

I'm sure I'll have more questions and again sorry if this already exists in other threads.

THANK YOU.

If the trv and annua are at all green and you've got the Tenacity? Hit it and don't quit it. :-) Make it hurt. Make it suffer. Give it some pain. Even if it isn't absorbing all of it, it'll get some and it'll be uncomfortable. Sure, the timing's not perfect, but who cares? It's a start. Just call it this year's May/June application and say you were late with it. Been there, done that, liked the results.

Triv and annua are much more pervasive than most will give them credit for. My lawn is pretty much 100% full sun everywhere except a few spots. It broils. I don't irrigate. I still get the stuff. Sigh.

"I take it then that Tenacity is not an effective pre-em for Triv (and Annua, for that matter?). Related to this then, when should I put down the Prodiamine? I think Annua germinates in the fall around these parts. I want to say Oct/Nov? What about Triv?"

Tenacity is a great pre-em for both, but really short-term, about 30 days from application. So if we're applying it at the right time to knock it down--June and November--we're getting coverage at the wrong times for sprout (your correct second month is probably October with your colder weather and sprout is probably late August through September).

Prodiamine from the bottle can be applied in any shield from about 2 to 9 months on our northern lawns, adjustable just by changing the amount you're putting down and the clock stops in winter, so our apps can actually cover us for crabgrass the following summer if we want (it's not perfect but it does help).

Dimension is another good one that works and you can simply buy bags of that at the big box store if you want. The shield is usually shorter, but it works fine, doesn't require being out there spraying the stuff (I don't mind, some do) and can be combined with your Labor Day feeding if you'd rather just by doing a second step.

Tenacity is the third option. It's a 30-day pre-emergent that you can use when you seed.

New grasses can't be seeded through the pre-emergents--except Tenacity, like I just said above. It bears repeating. So if you want to seed this season, you'll want to use Tenacity at the recommended rate when you seed. It'll keep the triv and annua from taking over the seeding bed.

Frankly, the easiest way (and one I don't normally recommend but I'm OK with it where somebody has a widespread problem) is to use Starter Fertilizer with Mesotrione. Which is Tenacity. At bag rate, it'll apply the correct amount and one shot of starter is OK with me on pretty much any soil. Knowing most northeastern soils, it's not going to be an issue.

And always ask. It's easier to concentrate the answers in one thread than try to find the diluted answers in the forum. If the concentrate already exists in the can, we'll point you there. Let me know if I missed anything in the above can, too.

I will absorb this, take action, keep you updated, and I'm sure will post more questions as I think of them. A million thanks again!

Okay - here's a follow-up: your comment

Prodiamine from the bottle can be applied in any shield from about 2 to 9 months on our northern lawns, adjustable just by changing the amount you're putting down and the clock stops in winter, so our apps can actually cover us for crabgrass the following summer if we want (it's not perfect but it does help).

I just want to make sure I understand this. Are you saying the effectiveness of the pre-em can last between 2-9 months, depending on amount applied? If the clock stops in winter (aka I read that as winter disrupts the pre-em shield?) - how would it still cover for the following summer?

In short - first order of business for me is to prevent new Triv and Annua from germinating. So thinking I would apply Prodiamine in liquid form in the fall. When do you suggest?

And then next year, possibly in spring but more in earnest NEXT fall, I'd be looking to overseed again. does that make sense?

Thanks!

If I'm not mistaken, the max recommended prodiamine yearly rate does not cover 12 mo. The more you put down the longer it does last but overdo it in some areas and you will have dead grass. With this drought and heat spell, I am noticing that areas that I have pre-emergent from april have taken a huge hit compared to areas that did not get it. I am glad I didn't put down a whopper dose because I may need to reseed in August!

It won't kill the grass (I've accidentally overapplied it), it just doesn't last much longer than the maximum length of time, plus clock stoppage for winter. The microbes simply accelerage and eat it faster.

Mish, you actually shouldn't be seeing additional damage in pre-em applied areas as the shield is heavily soil-binding and sticks in the top quarter inch, well above any water-seeking grass roots. Is there something else peculiar to that area that usually results in weed growth?

The clock stops in winter in the sense that the microbes aren't eating away at the shield. If you put down a 6 month shield in September, you use 3 months through December, and the clock re-starts in March or so and covers through June to cover for the spring weeds. It's not perfect (last winter did cost time as it was pretty warm).

The difference is in treated areas vs not treated is stark. It's tge only thing that I've done differently. IIRC, there was a user in Chicago who reported killing his whole lawn from over applying the pre em. I don't know how much over he went though.

That seems very strange. I've more than doubled due to a mental slip and never even noticed--on lawn that's short-rooted (bluegrasses not being notably sturdy about such things) and rather sensitive--allegedly--to over-application.

Which one did you use?

okay resurrecting this one. I posted the original here and just following up. So since July, we've had pretty extended drought and heat (well it's been cooler the past few weeks now with autumn sun angle...). My poa triv is STILL dormant ( know better than to say dead). I was waiting to hit with Tenacity as Morpheus suggested above, but haven't because presuming it's so dormant in ain't growing thus the effect of Tenacity is a waste.

Any suggestions on what to do now?

Also - have some prodiamine granular form and will apply this weekend (for some poa annua in same areas for the most part as the Triv). I have and will reread the directions for how much to use for pre-em time - thinking from now thru the early spring months as well so a few months, minus the winter temps. Is there any trick to calculating? Seems like all based on acreage and I'm talking just a few 100 square feet I'd like to treat with probably 1 tank sprayer. I understand it's not the amount of water that's used but the amount of prodiamine applied within that tank sprayer. I'm sure I can literally calculate it out with square footage vs an acre but seems like I'm splitting hairs at that point.

Any advice appreciated!

Thanks!

Hold the Tenacity for now. If the roots aren't awake, it won't work. We're in the same dry spell you are and I've stopped mowing.

There's a trick for Prodiamine--tablespoons per thousand square feet is identical to ounces per acre. So for most lawns, app 1 to 1.5 Tbsp per thousand square feet, which is the equivalent of 1 to 1.5 ounces per acre. For most lawns, the target is going to be around 1. For mostly-bluegrass lawns, 1.5 is fine.

Simply adjust that for however many hundred square feet that is. Side note: This stuff also works on patios and sidewalk cracks. Just sayin'.

Great! Yes but isn’t there a variation to figure out how much to use for how long of protection? If I’d like 5 months of protection vs 8? Or am I splitting hairs here?

In other words how many months will 1 tbsp per gallon per 1000 sq ft protect? What if I’d like a few months more? (Of course I can reapply in the spring I guess)

1 tablespoon per thousand (however you dilute it) lasts about 5 1/2 months. However, it gets weird over the winter...when soil temps drop under about 45, the barrier doesn't decay very fast. When they drop under 32, decay essentially stops.

Ah yes. I shouldn’t have specified the 1 gallon. Just the tablespoon per area. Yes this helps to know it’s about 5.5 months, not including the funky winter slowdown. That should do it. Thank you!

Also on the dormancy and Tenacity - the rest of the lawn has woken up with lower temps, although we are still in severe drought. At this point, and IF the triv starts coming back - should I hit it. Or wait until spring?

Hit it, by all means. It'll be damaged by drought, you might as well give it some pain from Tenacity as well just before winter!