Too late for pre-emergent

Discussion in 'Pesticide & Herbicide Application' started by Larson Lawn Care, Apr 2, 2010.

  1. Larson Lawn Care

    Larson Lawn Care LawnSite Senior Member
    Posts: 738

    A mowing customer of mine asked me if it was too late for a pre emergent, I told him I had no clue, but the weeds may already be growing. What can I tell him?
     
  2. clydebusa

    clydebusa LawnSite Bronze Member
    Posts: 1,660

    The big question for pre-emergent weed killers is when to apply them. Pre-emergent herbicides only work if they are applied to your lawn before the weed's growth period. But if applied too early, weather will dilute the herbicide and the weed will grow unencumbered.
    Two dates to remember are March 15 and September 15. Those are the two dates of the year around which pre-emergent fertilizers should be applied so that they activate before seasonal weeds make an appearance.

    Ofcourse this could change depend on the zone you are in. In St Louis you could go closer to April.
     
  3. Larson Lawn Care

    Larson Lawn Care LawnSite Senior Member
    Posts: 738

    So its too late?
     
  4. grass4gas

    grass4gas LawnSite Senior Member
    Posts: 473

    It is all based on soil temps. When soil temps hit 55 degrees for 4-5 days in a row, crabgrass will begin to germinate shortly thereafter.

    What are your daytime temps in St. Louis? If you been having cool temps, you are fine.

    Get a soil thermometer or check with your local extension office.

    My theory is even if crab has germinated, put a pre down anyway. You are going to get a certain % of control as it is. Putting nothing down means no control of any kind.
     
  5. Turfdoctor1

    Turfdoctor1 LawnSite Senior Member
    Posts: 705

    grass4gas is right.

    Preventing crabgrass is your main goal when putting out your spring pre-emergent. You may have a little effect on broadleaf weeds, but not much. The main emphasis is getting the crabgrass prevented.

    It is recommended to have it down by now, but you are still fine. I'm several hours south, and we certainly have not seen any crabgrass germination yet. You are without a doubt still ok up there.
     
  6. Boomer Sooner

    Boomer Sooner LawnSite Member
    Posts: 40

    Apply Liq Dimension with msma, if you catch it in early stages,it will get most of it,crabgrass is not up yet, but I expect to see some this next week in Tulsa, broadleaf weeds will be controlled with the post app- most of time it takes a full season to control crab,theres no miracle wonders in one app
     
  7. jose85

    jose85 LawnSite Member
    Posts: 214

    just like the guy said , its always ok as long as the soil temp is still below 55


     
  8. SOONER GREEN

    SOONER GREEN LawnSite Member
    Posts: 77

    No it's not too late. Like they said, soil temps above 55 for @ 5 days will germinate crabgrass. I saw crabgrass in the single leaf stage today in my neighbors yard which is a south facing slope with sandy soil. The Oklahome mesonet shows the 3 day average 2 " under sod is 57, so it wont be long.Thats early for OKC, it's normally @ April 15th. Rd. 1 is fixin to come to an end.
     
  9. RigglePLC

    RigglePLC LawnSite Fanatic
    Posts: 11,770

    If....you have frost...it kills crabgrass. So maybe you have a few more days. We used to figure that the last day for crabgrass control was the first frost-free-date in your city. About May 22 for us. If tiny crabgrass seedlings are not visible--it may work. Otherwise partial control.
     
  10. Larson Lawn Care

    Larson Lawn Care LawnSite Senior Member
    Posts: 738

    It was in the 70's/80's for a week here in St. Louis.
     

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