Pinoxaden is a POST acetyl coenzyme A carboxylase (ACCase) inhibitor in the phenylpyrazolin chemical family and is labelled for turfgrass use at broadcast rates of 35.5 to 71 g ai ha–¹ and spot spray rates of 156 to 310 g ai ha–¹. A greenhouse rate-response study was conducted to characterize the efficacy of pinoxaden against common grassy weeds. Weed species examined in this study were yellow foxtail, southern sandbur, annual bluegrass, roughstalk bluegrass, large crabgrass, dallisgrass, bahiagrass, goosegrass, and perennial ryegrass. Nonlinear regressions were modelled to determine visible injury rates (the application rate at which 50% of the weed species were injured and the 90% [I₉₀] rate) and weight reduction rates (the application rate at which there was a 50% reduction in fresh weight and 90% reduction [WR₉₀]) for each weed species. Only annual bluegrass, bahiagrass, and goosegrass had visible injury I₉₀ values greater than the maximum labelled spot spray rate of 310 g ai ha–¹. Annual bluegrass, bahiagrass, southern sandbur, and goosegrass all had WR₉₀ values greater than the maximum labelled spot spray rate of 310 g ai ha–¹. Results from this study indicate that the evaluated weed species can be ranked, according to visible injury I₉₀ values, from most to least susceptible: perennial ryegrass > yellow foxtail > dallisgrass > large crabgrass > southern sandbur > roughstalk bluegrass > bahiagrass > goosegrass > annual bluegrass.

Nomenclature: Pinoxaden; annual bluegrass, Poa annua L.; bahiagrass, Paspalum notatum Fleugg.; dallisgrass, Paspalum dilatatum Poir.; goosegrass, Eleusine indica (L.) Gaertn.; large crabgrass, Digitaria sanguinalis (L.) Scop.; perennial ryegrass, Lolium perenne L.; roughstalk bluegrass, Poa trivialis L.; southern sandbur, Cenchrus echinatus L.; yellow foxtail, Setaria pumila (Poir.) Roem. & Schult