Tenacity as only pre-emergent

Discussion in 'Homeowner Assistance Forum' started by nunnink23, Apr 14, 2019.

  1. nunnink23

    nunnink23 LawnSite Member
    Messages: 15

    I am relatively new to lawn care - I attempted a lawn renovation on my home in the fall of 2017 with moderate success. The lawn came in relatively strong (Connecticut, mostly sunny & flat landscape). Before reseeding I tilled the land and added 4" of fresh topsoil, but I didn't achieve full coverage in the fall. I decided in the spring of 18 that it made more sense to overseed and focus on thickening up the lawn rather than using a pre-emergent. Unfortunately this plan backfired. As soon as the summer weather hit my lawn went completely dormant and an indescribable amount crabgrass emerged. I tried using Quinclorac to control it but that only seemed to slow it down.

    In the fall of 2018 I hand picked every last blade of crabgrass from the lawn and reseeded once again. It was at that time I did a soil test and realized my PH was 5.5. I have been able to get it up to 5.8 so far, and just applied lime again (should be around 6.0 after this app). My dilemma is choosing between successful overseeding (I have a dog who tore the lawn up over the winter), and using a powerful pre-emergent such as Prodiamine or Dithiopyr. My current plan was to use Tenacity so I could seed and prevent crabgrass, but I am starting to have second thoughts. I put Tenacity down last weekend when soil temps were about 50 degrees. From what I understand I would need to reapply Tenacity every 3-4 weeks until late summer in order to prevent crabgrass. I am okay with this strategy if it allows me to successfully overseed this spring & fall, but if I end up with a crabgrass issue as bad as last year I will regret not using Dithiopyr (I think its too late for prodiamine now).

    Any thoughts on using Tenacity as your ONLY pre-emergent? I have some other pesky weed in the lawn as well that I would like to get rid of. Its only in one area of the front yard but I am starting to see it pop up in small sections of the remainder of the lawn. It doesn't look like clover to me - any ideas on what this is as well?

    Thanks all.


  2. FdLLawnMan

    FdLLawnMan LawnSite Bronze Member
    Messages: 1,410

    Tenacity is the only thing you can use if you want to reseed. Crabgrass should be done germinating by late June. Tenacity also prevents a range of broadleaf weeds. You cannot seed if using prodiamine or diothypyr.
  3. OP

    nunnink23 LawnSite Member
    Messages: 15

    Thanks for the reply. I should have clarified that the decision I’m struggling with is between accepting some bare spots (due to overseeing failure) due to using dithiopyr, or seeding and using Tenacity. I’ve already thrown seed down in bare spots with some peat moss and hit the whole lawn with Tenacity. I’m now wondering if I should abandon the overseed plan until this fall and use Dithiopyr everywhere except the worst bare spots with a liquid application. The last two years have been a vicious cycle of fix the lawn through seeding, have it destroyed by crabgrass, rip the crab grass out and reseed, repeat. It’s likely not too late to use dithiopyr if you guys think Tenacity won’t be effective as a crab Pre-emergent. That’s my main question - is Tenacity an effective pre-emergent in your experience.

    DITCHDIGGIN LawnSite Member
    Messages: 65

    I used Tenacity on 2 yards last year for my pre emergent crabgrass control mainly just because I was curious. Normally I'm using Dimension or Barricade. One app of Tenacity towards the middle of May with favorable results. Both yards were fairly nice and the only drawback was the bleaching spots for a couple weeks. Didn't have to deal with any bare spots though so that may be different. You're not to late to put down Dimension or Barricade. Weed pictures look like chickweed.

    Yeah right.
    hort101 likes this.
  5. OP

    nunnink23 LawnSite Member
    Messages: 15

    So it sounds like Tenacity was effective in preventing crab in your case. I have read mixed reviews. One thought was using a wettable Dithiopyr everywhere except the bare / thin spots. I attached a few photos of my bare spot. This spot never had a chance to establish because my dog likes to run and pivot 180 in the same spot every day. I am going to keep it fenced off for a few months to let it fully establish. PH wasn't helping either as this was the most acidic area of the yard for some reason.

    I would prefer to use Tenacity without Dithiopyr since I plan to overseed again in the fall (I messed up and sowed in some TTTF to my KGB/Rye mix and it sticks out like a sore thumb). I was going to try to choke the TTTF out by continuously adding more KBG every spring and fall.

    Do you think I will be happy with the efficacy of Tenacity for crab pre-emergent if I apply once every 3 weeks (label says 21 days pre-emergent ability)? Next year hopefully I don't need to seed and I can just use Dithiopyr and call it a day.

    BTW you can see the bleaching from the Tenacity app 2 weeks ago.




  6. RigglePLC

    RigglePLC LawnSite Fanatic
    Messages: 16,398

    Agree, looks like chickweed (white flowers). Tenacity now is good--or Dimension, which would last longer. Follow up with Drive if you think it is necessary. Then seed in late summer.
    The grass is a bit clumpy--this may be due to the high level of perennial rye in the mixture. Seed it thick as it does not creep. Crowding out tall fescue will be difficult. The bluegrass variety "Arcadia" is very dense--this is a good option in your case. But feel free to dig out clumps of Tall fescue by hand.

    And yes, put a couple lawn chairs or picnic tables to block the dog away from the thin spot he made lat winter.

    Seed about the date in August when daily high temperatures fall below 85. Or 8 weeks before average frost in your town, whichever is earliest.
    Let the grass get tall for an extra week. Let the crabgrass (if any), get tall, then cut everything, then cut again, extra short. Shocks the crabgrass. Remove residue--later you can probably use it for mulch in place of straw.
    Apply starter fert, seed (at 8 pounds per thousand sqft), and lots of water.
    The new seed should germinate quickly, because the soil temperatures will still be warm.
    Cooler and cooler nights, 2 weeks later, will prevent much growth of the crabgrass--a temperature of about 45 stops further growth--hard frost kills crabgrass.
    Naturally, apply prodiamine or Dimension next spring. Follow up with a second application of Dimension or prodiamine, after about 6 weeks in 2020.
    Last edited: Apr 15, 2019
    zlandman and hort101 like this.
  7. FdLLawnMan

    FdLLawnMan LawnSite Bronze Member
    Messages: 1,410

    Tenacity is very effective in controlling crabgrass. I would go the tenacity route.
    hort101 likes this.
  8. OP

    nunnink23 LawnSite Member
    Messages: 15

    Drive isn't available in CT, but I bought QualiPro Quinclorac which is just less concentrated I believe. This should be effective on young crabgrass from what I understand - but it doesn't seem to be making a dent in the chickweed. I sprayed it last weekend & this weekend. To be fair, I don't have MSO (ordered it this morning) so I have been using the ionic surfactant that Tenacity calls for. Should I be using something different for the chickweed?
  9. hort101

    hort101 LawnSite Fanatic
    Male, from S.E. New England
    Messages: 20,044

    Imo dont obsess over it its a cool season weed if its a big clump rip it out use a weeding tool if needed and seed

    Also if you mow and bag it will help lessen seeds of most weeds

    Pre in the late fall should help get rid of cool season weeds for next spring
    Walker56 likes this.
  10. OP

    nunnink23 LawnSite Member
    Messages: 15

    So I tried to rip them out this weekend but it seems like they have a massive footprint. Does that make sense to you? If I rip it out I think quite a bit of lawn will come with it.

    So chickweed won’t grow back this spring/summer if I remove it now?

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