Selective mode of action of orbencarb in wheat and crabgrass.

The herbicidal selectivity of orbencarb, S-(2-chlorobenzyl) N, N-diethylthiocarbamate, was investigated in several species of gramineous plants. Plants tolerant to the herbicide were wheat, oat and upland rice and those susceptible were corn, finger millet, barnyardgrass and crabgrass. Lowland rice was intermediate in tolerance.The absorption, translocation and metabolism of 14C-orbencarb were studied to clarify the mechanism of its selectivity. The rate of its absorption by shoots or roots was much higher in crabgrass than in wheat. Orbencarb moved acropetally when applied to either shoots or roots, and the rates of translocation from roots to shoots did not greatly differ. The metabolites of 14C-orbencarb were partitioned and identified by thin-layer chromatography. Rates of orbencarb metabolism in wheat and ceacgrass were found similar, although the monodesethyl orbencarb metabolite was produced much more in wheat and the hydroxy orbencarb metabolites were detected only in wheat. Absorption by shoots is considered to be a major process contributing to the selective mode of action of orbencarb in wheat and crabgrass.