After using Spectracide® Weed Stop® for Lawns how long before the grass is safe to eat?

Question

A friend has a lawn that has been treated with Spectracide® Weed Stop® for Lawns, and she has rabbits that she would like to allow graze on the lawn. Following the links from the Manufactures site it looks like the active ingredients are

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

The information sheet says: "Do not apply this product to food crops,(or) forage crops.."

If a lawn has been treated, how long is it before rabbits (or herbivores in general) can be allowed to play on and eat from the lawn?

Answer 1

Also answered here.

• 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.

  (source)

• 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)

  (source)

• 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.

  (source)

• 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.

  (source)

Note: These numbers show the half-life. Parts of the chemicals may be present in the soils years later. I would recommend a waiting period of at least two years, just to stay on the safe side, before letting rabbits regularly graze the area.