Absorption, distribution and metabolism of bifenox

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Virginia Polytechnic Institute and State University


The fate of bifenox [methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate] in soil and plants following preemergence application of this herbicide, was investigated in greenhouse and laboratory studies. Radiolabeled ¹⁴C-bifenox had a half-life of 3 to 7 days after application to the soil and was characterized by hydrolysis to 5-(2,4-dichlorophenoxy)-2-nitrobenzoic acid. The acid was found to be highly mobile in a soil elution column, accounting for the short half-life in soil as a result of leaching of the acid. Additional metabolites identified in the soil included: 2,4-dichlorophenyl-4-nitrophenyl ether and 5-(2,4-dichlorophenoxy) anthranilic acid. Comparison of the total ¹⁴C in the sampling zone of 8 cm to that extractable by methanol showed increased binding of the compounds to the soil over a 313-day period.

The uptake by plants was rate dependent in the range of 1.7 to 4.5 kg/ha, preemergence application. Velvetleaf (Abutilon theophrasti Medic.), a weed susceptible to the herbicide, absorbed and translocated more ¹⁴C-bifenox during early seedling growth than corn (Zea mays L.) and soybean (Glycine max (L.) Merr.).

The patterns of absorption and distribution of ¹⁴C-bifenox, were different among corn, soybean, and velvetleaf. Autoradiographs of seedlings growing in treated soil showed the ¹⁴C to be confined to those areas of the crop plants in contact with the soil during emergence. Velvetleaf absorbed and translocated the labeled compound(s) to all areas, including the immature leaves. Root absorbed ¹⁴C-bifenox from nutrient culture was transported in equal quantity to the shoots of the three species. However, in corn and soybean the ¹⁴C-compound(s) was confined to the primary and secondary leaf veins while velvetleaf showed a general distribution of ¹⁴C throughout the leaf tissue.

The test species were capable of metabolizing ¹⁴C-bifenox after root absorption from nutrient culture. Tissue macerates of the shoots of corn and soybean in vitro did not metabolize the bifenox, velvetleaf hydrolized it to the acid but to less than 1% of the total incorporated.