The performances of several herbicides incorporated to a depth of 2.5 and 7.6 cm in sandy loam and sandy clay loam were studied in cabbage plantings in 3 field experiments. Herbicidal activity of O, O-diisopropyl phosphorodithioate S ester with N -(2-mercaptoethyl) benzenesulfonamide (bensulide) and a,a,a-trifluoro-2, 6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) was outstanding. These herbicides controlled Palmer amaranth (Amaranthus palmeri S. Wats.), redroot pigweed (Amaranthus retroflexus L.), common purslane (Portulaca oleracea L.) and barnyardgrass [Echinochloa crusgalli (L.) Beauv.] without reducing yields of cabbage (Brassica oleracea, var. capitata L.) ‘Improved Globe YR’. Dimethyl tetra-chloroterephthalate (DCPA) and 2-chloroallyl diethyldithiocarbamate (CDEC) were less effective. Trifluralin performed more efficiently when depth of incorporation was 7.6 cm compared to 2.5 cm. CDEC performed better when incorporated at a depth of 2.5 cm. Performance of bensulide and DCPA was unaffected by depth of incorporation.
Bioassays indicated that regardless of rainfall, bensulide, DCPA, and trifluralin remained within the original soil zones of incorporation. Trifluralin persisted longer in the soil as depth of incorporation was increased. Under high temperatures, infrequent rainfall, and furrow irrigation, the half-life of trifluralin treatments was 1 to 2 weeks; there was no measurable biological activity in treatments incorporated to 2.5 cm after 3 to 6 months, or after 9 months when treatments were incorporated 7.6 cm. The half-life of DCPA was 1 month with no activity after 6 months regardless of incorporation depth. Bensulide was most persistent, with no activity 12 months after the 2.2 kg/ha rate, and 24 months after the 4.5 and 9.0 kg/ha rate of application, regardless of incorporation depth.