Glufosinate efficacy was examined in two major grass weed species, rigid ryegrass and sterile oat. Dose–response pot experiments under controlled environmental conditions showed that sterile oat was more successfully controlled by glufosinate than was rigid ryegrass. Glutamine synthetase was extracted from both species and assayed in vitro. Glufosinate readily inhibited glutamine synthetase activity in both species, indicating no differential sensitivity to the target enzyme. Thin-layer chromatography analysis of glufosinate showed no significant metabolism of glufosinate in either species. Absorption and translocation studies with ¹⁴C-glufosinate showed that the radiolabel was rapidly absorbed into the leaves of both species. However, translocation of radiolabeled glufosinate from the treated leaf to the meristematic regions was significantly greater in sterile oat, whereas translocation to the tip of the leaf was significantly greater in rigid ryegrass. This indicates that there is a difference in glufosinate distribution between the two species. It is likely that this difference in the distribution of glufosinate results in sterile oat being more easily controlled by glufosinate than is rigid ryegrass.

Nomenclature: Glufosinate; phosphinothricin; rigid ryegrass, Lolium rigidum Gaud. LOLRI; sterile oat, Avena sterilis L. AVEST.