Once a lawn has been treated with Spectracide® Weed Stop® for Lawns how long are the active ingredients 'active'? Do some decay faster then others?

Following the links from the Manufactures site it looks like the active ingredients are

  • 2,4-d, dimethylamine salt
  • Quinclorac
  • Dicamba, dimethlyamine salt
  • Sulfentranzone

This is companion question for related question on Pets.SE


2 Answers 2

  • 2,4-D: 10 days, up to 333 in wet areas.

    2,4-D degrades fairly quickly in soils (half-life about 10 days for acid, salt and ester forms), with microbial degradation considered to be the major route in the breakdown of the chemical in soil.It is, however, relatively persistent in anaerobic (low oxygen) aquatic environments (half-life ranges from 41 to 333 days). This has implications for fragile wetland areas, especially those under conservation.


  • Quinclorac: from 18 to over 500 days.

    Quinclorac is not expected to dissipate into the air or breakdown with interaction with water (hydrolysis). In sterile water it is resistent to breakdown by sunlight but in muddy water it degrades much faster (5-10 days). In soil, quinclorac has dissipation values that range from 18 days to over 500 days. Because quinclorac does not bind well to soil, some dissipation noted in field testing could be due to chemical leaching. The persistence hazard of quinclorac is rated high (likely to take over 60 days to degrade to half of the applied concentration)


  • Dicamba: 7 to 42 days, depending on soil texture.

    Under aerobic conditions in soil dicamba degrades with half-lives ranging from 1-6 weeks, depending on soil texture. Degradation rates are slowed by decreasing temperatures (<20 degrees C) and decreasing soil moisture below field capacity.


  • Sulfentrazone: 24 to 113 days.

    Sulfentrazone dissipation in soil was examined in field experiments in 1995, 1996, and 1997 at Knoxville, TN, on a Sequatchie loam soil. Sulfentrazone 50% disappearance time (DT50) varied from 24 to 113 d.



Having checked the question on Pets.SE, you seem to want to know when it will be safe for rabbits to graze the treated area. As with all liquid lawn weedkillers, once the spray or solution has dried, it's safe for animals and children to use the lawn, though 24 hours elapse is safest. For grazing animals though, it is not safe if that is their only food source on a daily basis. Looking at the Q & A section for this product displayed on the link you provided, re-application can be made 3 weeks later, which strongly suggests a minimum of 3 weeks, but usually, the time elapse between treatment with a product of this nature and the grass itself being safe to consume is 6 weeks. It may be longer if the weather is very dry and the rate of grass growth is slow.

If you're still not sure, if you click on the Question and Answer tab lower down their page, you are able to post a question there directly to the manufacturer.

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