AbstractA novel compound, 1‐(3‐trifluoromethylphenyl)‐5‐phenoxy‐1,2,3,4‐tetrazole (WL 110547) is a pre‐emergence bleaching herbicide with selectivities in certain crops. These selectivities and the weed‐control spectrum are derived, in part, from features which influence the uptake of WL 110547 into sensitive tissue. WL 110547 is strongly adsorbed to soil with measuredKocvalues in the range 1500‐2500 and, following application, is confined to the surface layers of soil, especially when the organic matter content is high. Some plant species have anatomical features which protect their developing leaf tissue from contact with the soil during emergence and thus escape direct contact with these treated layers. Furthermore, some of these plants are deeply rooted and thus there is little opportunity for sufficient uptake of WL 110547 to cause a phytotoxic effect.However some weeds, especially annual dicotyledons, germinate only from shallow depths and, during emergence, their cotyledons or leaves are in contact with the soil. In soils treated with WL 110547 they can thus absorb phytotoxic concentrations of herbicide directly into their cotyledons or leaves. Additional uptake may also occur through roots near the surface and allow WL 110547 to be translocated via the transpiration stream to the site of action in cotyledons and leaves and enhance phytotoxicity.Knowledge of the features controlling uptake, combined with a knowledge of intrinsic susceptibility, have allowed an understanding of the spectrum of weed control and the selectivities betwee