Phytotoxicity of Bensulide and Trifluralin in Several Soils

Seedlings of 19 plant species were grown in soils containing 0 to 1,000 ppm of O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide (bensulide) or 0 to 100 ppm of a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) to determine phytotoxicity. Standard growth curves were constructed. The concentration of bensulide required to reduce the growth of shoots 50% (GR50) ranged from 1 ppm with barnyardgrass (Echinochloa crusgalli (L.) Beauv.) to more than 1,000 ppm with carrot (Daucus carota L., var. Long Imperator). Several plant species were more sensitive to bensulide in a Hidalgo sandy loam (pH 8.1) than in other soils including a Delfina loamy fine sand (pH 6.0). The concentration of trifluralin required to reduce the growth of shoots 50% (GR50) was not markedly affected by soil texture and ranged from 0.1 ppm with German millet (Setaria italica (L.) Beauv.) to more than 100 ppm with Long Imperator carrot. The standard growth curves have been used to quantify herbicidal activities in field soils.