Opinions about pre-emergents

Discussion in 'Pesticide & Herbicide Application' started by LawnRunner, Dec 21, 2007.

  1. LawnRunner

    LawnRunner LawnSite Member
    Posts: 37

    Hey Everyone,

    I was sitting around thinking today about liquid pre-emergents and would like to know whether:

    The pre-emergent coats the soil to keep weed seeds from germinating or
    The pre-emergent coats the seeds to keep them from germinating or
    The pre-emergent coats the soil and seeds to keep them from germinating.

    In other words if you spray a pre-emergent on the turf and then later break the barrier would the seeds that were there at the time of the spray then germinate?

    Thanks for your comments
  2. 413golf

    413golf LawnSite Member
    Posts: 50

    Hey thats agood question ,I was uner the impression that preemergants where soaked up by specific plants and not others.I'll get back with you in a few because I need to know or I'll be up all night trying to figure it out
  3. LawnTamer

    LawnTamer LawnSite Gold Member
    Posts: 3,988

    This is actually a much debated topic because of aeration. There is good solid data you can get from the manufacturers about this. Different pre ems move through soil differently and at different rates. Prodiamine, (Stonewall, Barricade) tends to stay in the top .5-1", pendimethilin moves deeper into the soil, down to about 2" if I remember correctly. I'm not sure of Dimension as I don't use it myself. It also depends on soil composition.

    As far as aeration Iowa st and one other school, Ohio st I think, did a plot test and there was virtually no difference.
  4. 413golf

    413golf LawnSite Member
    Posts: 50

    well I did some studying and appear to know less than I did.It says they prevent seedling from germinating. It's stays in the first two inces of soil and zaps the seedlings before they germinate,like I said I know less now than I did:laugh: Golfcourse do it around the same time
  5. rcreech

    rcreech Sponsor
    Male, from OHIO
    Posts: 6,057

    This is exactly what I heard! Was at a summer OTF this summer and they said that the advantages of core aeration outweighed the disadvantages breaking the barrier.

    As far as how a chemical works depends on the mode of action.
  6. LawnRunner

    LawnRunner LawnSite Member
    Posts: 37

    Its me again

    I just wanted to mention why I was thinking about how pre-emergents work. Poa Annua and now Poa Trivialis is and has been a big problem to control. The light green color of the Trivialis looks terrible in a dark green fescue lawn. The reason these weeds are difficult to control is because the seeds germinate about the same time as the disirable grasses.

    What I was thinking was spray the lawn with a pre-em at the end of summer before Poa seeds start germinating. If the pre-emergent also coats the seed then it would keep those seeds from germinating in the fall. In the fall you could aerate or slit seed, which would break the barrier. Then overseed with fescue or other desirable seed.

    Has anyone done this to help control Poa? Maybe this would work but then again if the seed you buy is contaminated then you would be fighting a losing battle. See where thinking will get you.
  7. turfsurfer

    turfsurfer LawnSite Senior Member
    Posts: 364

    Your main problems would be:
    1) There would probably be enough residual pre-emergent left in the fall to hamper seeding success.
    2)slice-seeding and core-aeration would probably not be enough to seriously disrupt the pre-M barrier. Once a good rain hits the barrier would just re-establish as the plugs break down.
    It's my understanding that as the new seedling pushes up and contacts the Pre-M barrier, it is killed.
  8. rcreech

    rcreech Sponsor
    Male, from OHIO
    Posts: 6,057


    This should answer your questions. Again, you need to know how the chemical is taken up by the plant and how it kills the plant, which is known as the mode of action.

    Here are two sites that will help you. I think everyone should want to know this info if they don't already. It helps you to understand how to apply the product SO IT WILL WORK.

    I know people (some on my customers) that spray Glyphosate on bareground and then when weeds emerge they think it didn't work! DUH! That is why this is important! You have to know how the chemical works for it to be effective

    In the first attachment look at the slide 35 and on and it talks about pre's mode of action as they limit cell division.

    To answer you question...all weeds have to emerge to be killed. In this case the product has to come in contact with the root system of the plant and kills the plant by limiting their cell division growth. In most instance with all modes of action you are just starving the plant and it dies.

    The only way to keep a seed from germination to my knowledge in FUMIGATION!


    Also look at the first attachment....didn't we talk about selective and non-selective products a while back? See what they have to say! Look at slides 7 and 8.


  9. naughty62

    naughty62 LawnSite Senior Member
    from iowa
    Posts: 368

    In my opinion the biggest misconception is that most pre Ms prevent germination .They kill the newly germinated plant through contact.I have never dissected the modes of action on most of common turfgrass products what really jerks my chain is when someone buys the the bargain of day combo product and the a.i./fert ratio is totally inappropriate for our program or conditions.I am not fond of some combo products with huge prill sizes .
  10. Ric

    Ric LawnSite Fanatic
    Posts: 11,956


    Let me answer your original question as ask. (Ronstar being the big Exception and not labelled for Residential)

    Pre-emergents works by Creating a barrier on the top layer of the soil. The deeper the barrier the more effective. It does not stop the seed from Germinating. When seeds germinate they first send out a Hair (cingular) root. It is the hair root that is effected by the pre emerge and cause the seed to fail to grow. Because of this effect on hair roots, Many including myself, feel Pre emergents cause chemical root pruning. Because the same ground temperature is the big factor in both Germination and Rhizome production. As stated before, Hollow Core Aeration does not hurt the barrier of Pre Emergents.

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