Susceptibility of a broad‐leaved weed, Acanthospermum hispidum , to the grass herbicide fluazifop‐butyl

Broad‐leaved plants are generally resistant to aryloxyphenoxypropionate (AOPP) and cyclohexanedione (CHD) herbicides. In laboratory experiments, however, we confirmed that Acanthospermum hispidum , a Compositae weed, was susceptible to one of the AOPP herbicides, fluazifop‐butyl, but tolerant to other AOPP herbicides (quizalofop‐ethyl and fenoxaprop‐ethyl) and a CHD herbicide (sethoxydim). The symptoms induced by fluazifop‐butyl in A. hispidum (wilting and necrosis) were distinctly different from those induced in oat (chlorosis). The period required to cause seedling death of A. hispidum (48–72 h) was shorter than that of oat ( ca 15 days). The ( R )‐enantiomer of fluazifop‐butyl was more active on this weed. In oat, lipid biosynthesis and acetyl‐CoA carboxylase (ACCase) activity were inhibited, and electrolyte leakage from the shoots was increased by fluazifop‐butyl and sethoxydim. In the case of A. hispidum , the membrane permeability increased and the lipid biosynthesis was inhibited only by fluazifop‐butyl. These results indicate that A. hispidum is particularly sensitive to fluazifop‐butyl, and its mechanism of action in the plant may be different from its mechanism of action in oat.