In greenhouse studies, the calculated I50 (herbicide application resulting in 50% inhibition of shoot regrowth) in tall fescue was approximately 0.004 kg/ha for both sethoxydim and haloxyfop. In red fescue, the I50 for sethoxydim and haloxyfop was 9.4 kg/ha and 0.04 kg/ha, respectively. As measured in crude cell extracts of tall fescue, incorporation of 14C-acetyl-coenzyme A into fatty acids was inhibited 62 and 71% by 10 μM sethoxydim and 10 μM haloxyfop, respectively. In red fescue, 10 μM haloxyfop inhibited 14C-acetyl-CoA incorporation into fatty acids by 29%, whereas 10 μM sethoxydim had no effect. The I50 for inhibition of acetyl-coenzyme A carboxylase activity in tall fescue with sethoxydim and haloxyfop was 6.9 and 5.8 μM, respectively. In red fescue the I50 for haloxyfop was 118 μM. Sethoxydim concentrations as high as 1 mM had little effect on acetyl-coenzyme A carboxylase activity in red fescue. These results suggest that acetyl-coenzyme A carboxylase is a sensitive site of action for sethoxydim and haloxyfop in tall fescue, and that tolerance to these herbicides in red fescue is due to the presence of a more tolerant form of the enzyme.

Field experiments were conducted in 1982 through 1986 to evaluate the effect of six postemergence grass herbicides, clethodim, the methyl ester of diclofop, the butyl ester of fluazifop-P, the methyl ester of haloxyfop, the methyl ester of quizalofop, and sethoxydim, on 31 seedling grass species. All herbicides except diclofop controlled most of the species tested. None of the herbicides controlled rattail fescue or red fescue. Only clethodim and haloxyfop controlled annual bluegrass.

Five perennial cool-season grasses: Kentucky bluegrass, creeping red fescue, tall fescue, orchardgrass, and perennial ryegrass were treated at the 2- to 3-leaf, 3- to 4-leaf, 4- to 6-leaf, and 6- to 7-leaf growth stages with four rates (0, 0.14, 0.28, and 0.56 kg ai/ha) of the butyl ester of fluazifop. Creeping red fescue was not injured by any rate at any growth stage. Reduction in shoot dry weight increased linearly with increasing fluazifop rate for the remaining four species, except for the 6- to 7-leaf stage in Kentucky bluegrass and the 4- to 6-leaf stage in tall fescue and perennial ryegrass. Significant differences between growth stages within each rate varied with species. In general, tolerance increased at the 4- to 6-leaf and 6- to 7-leaf growth stages.

Combinations of grass and legume mulches were planted in growing corn during the fall in 1985 and 1986, and the following spring no-till corn was planted into these living mulches. Mulch treatments consisted of a single species or grass plus legume mixtures. Fluazifop-P, 2,4-D, and atrazine were broadcast applied in late April to suppress the mulches and reduce their competition with corn. Chewings fescue and ladino clover competed least with dryland corn. Weed growth associated with chewings fescue and the ladino clover mulches was similar to that in the conventional disk-plant treatment, but corn yields were lower. Hairy vetch mulch was killed by 2,4-D. The winter rye mulch competed with corn and reduced yield.

Postemergence applications of BAS 9052 OH, {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, at 0.25 and 0.5 kg ai/ha were made to 27 temperate and 28 tropical species of Gramineae. Annual bluegrass (Poa annua L. ♯3 POAAN) and rattail fescue (Festuca myuros L. ♯ VLPMY) were resistant to these rates of BAS 9052 OH. Five species of fescue and three species of bluegrass received postemergence applications of BAS 9052 OH at rates of 0.1 to 6.4 kg ai/ha. The germination of seeds and the subsequent growth of the seedlings of these species as influenced by various concentrations of BAS 9052 OH were also studied. Meadow fescue (Festuca pratensis Huds. ♯ FESPR), tall fescue (Festuca arundinacea Schreb. ♯ FESAR), Kentucky bluegrass (Poa pratensis L. ♯ POAPR), and rough-stalked meadowgrass (Poa trivialis L. ♯ POATR) were most susceptible; annual bluegrass was somewhat less resistant; hard fescue (Festuca longifolia Thuill) was resistant; red fescue (Festuca rubra L. ♯ FESRU) and rattail fescue were very resistant.

Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} is used to control weedy grasses in red fescue (Festuca rubra L. # FESRU and F. rubra ssp. commutata), an important seed crop in Oregon. The sethoxydim rate required to reduce growth rate of 11 cultivars of red fescue and four cultivars of bentgrass (Agrostis tenuis Sibth. # AGSTE and A. stolonifera L. var. palustris # AGSST), a common contaminant in red fescue fields, by 50% (GR50) was determined in greenhouse and laboratory experiments. Field experiments compared only red fescue cv. ‘Pennlawn’ and bentgrass cv. ‘Penncross'. The GR50 values for Pennlawn red fescue in the field, the greenhouse, and the laboratory were 30 kg ai/ha, 15 kg/ha, and 5300 μM, respectively. Penncross bentgrass was approximately 400, 1400, and 12 900 times more susceptible than Pennlawn red fescue in the field, in the greenhouse, and in laboratory experiments, respectively. Plants were at different growth stages in the different experiments. The xylene and surfactant used as a solvent for the technical grade sethoxydim was as toxic to red fescue without sethoxydim as when sethoxydim was included. Cultivars of red fescue differed in their response to sethoxydim, but cultivars of bentgrass did not. The GR50's of other species tested in the greenhouse were >4 kg/ha for annual bluegrass (Poa annua L. # POAAN), 0.22 kg/ha for tall fescue (F. arundinacea Schreb. # FESAR), 0.37 kg/ha for downy brome (Bromus tectorum L. # BROTE), and 0.017 kg/ha for Italian ryegrass (Lolium multiflorum Lam. # LOLMU).