QBEEN is a systemic herbicide, absorbed from the leaf surface, with translocation throughout the plant, moving in both the xylem and phloem, and accumulating in the meristematic tissue. Growth ceases soon after foliar application, the actively growing tissues such as the intercalary meristem of grasses are affected first. Older leaf tissue may turn purple, orange or red before eventually becoming necrotic.

Selective post-emergence control of annual and perennial grass weeds in potatoes, soya beans, sugar beet, peanuts, oilseed rape, sunflowers, vegetables, cotton and flax.

The residue in plants
The maximum residues detected on fresh mint foliage at the proposed labeled level of product, Assure, of 0.2 pounds (lbs) active ingredient (ai) per acre (1x) applied 30 days before harvest were 0.22, 0.46, and 1.0 ppm for Indiana, Oregon and Washington, respectively. The largest residue found on fresh mint foliage, 2.6 ppm, was detected in a Washington sample treated with 0.4 lbs. Per acre (2x) 29 days before harvest, twice the maximum yearly rate allowed. At the level of Quantitation (LOQ) of 0.05 ppm, there were no detectable residue in the mint oil, either at the proposed label rate of 0.2 lbs. Ai/acre (A), or at the exaggerated rate of 0.4 lbs. Ai/A, indicating that quizalofop-p-ethyl and its acid metabolites are not concentrated during the oil distillation process. Adequate residue data were provided to support a tolerance of 2.0 ppm for mint. There are no livestock feedstuffs associated with mint.
Adequate residue data were provide to support proposed tolerances canola seed and canola meal. Processing data provide for canola seed indicated concentration in canola meal. Based on the concentration factor of 2.3x and the highest average field trial (HAFT) residue level of 0.65 ppm for canola seed, a tolerance at 1.5 ppm for canola meal is considered adequate.
Reference: http://www.epa.gov/EPA-PEST/1998/June/Day-16/p15746.htm