Movement and Persistence of Bensulide and Trifluralin in Irrigated Soil

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Abstract
Bensulide [0,0-diisopropyl phosphorodithioateS-ester withN-(2-mercaptoethyl)benzenesulfonamide] and trifluralin (α,α,α-trifluroro-2,6-dinitro-N,N-dipropyl-p-toluidine) were incorporated to a depth of 2.5 and 7.5 cm in sandy loam soil on the same plots in three annual applications to study the effect of incorporation depth on movement and persistence of the herbicides in furrow-irrigated soil. Bioassays and gas-liquid chromatographic assays indicated that, regardless of rainfall, both herbicides remained within the original soil zones of incorporation. Trifluralin persisted longer in soil as depth of incorporation was increased. Neither bensulide at 4.5 or 9.0 kg/ha nor trifluralin at 1.1 kg/ha persisted in appreciable amounts 12 months after treatment. At these rates, significant residues of bensulide and trifluralin were detected after 6 months only when tillage was restricted. Herbicide concentrations that persisted 6 months as determined in laboratory assays caused severe reduction in growth of field-grown sorghum [Sorghum bicolor(L.) Moench].