Abstract: Knowledge of optimal combinations of graminicide rate and stage of application could improve the effectiveness and net benefit of commonly used graminicides. A study was conducted at two locations in Saskatchewan, Canada, from 1994 to 1997. Factorial combinations of five graminicides (CGA 184927, fenoxaprop-p-ethyl, ICIA 0604, imazamethabenz, and flamprop-methyl), three graminicide rates (full, two-thirds, and one-third recommended label rate), and three leaf stages of wild oat (Avena fatua; two-, four-, and six-leaf) were compared to determine their effect on wild oat fresh weight, wheat (Triticum aestivum) seed yield, and net return. Wild oat fresh weight increased and wheat seed yield decreased to a greater extent at Saskatoon (median wild oat fresh weight of 56 g/m2) than at Scott (median wild oat fresh weight of 85 g/m2) when graminicide rate was reduced from the recommended label rate. Net return consistently decreased at both locations and among all graminicides when application rate was reduced from two-thirds to one-third of the recommended label rate. Imazamethabenz applied at progressively later growth stages caused greater wild oat fresh weight at both locations and reduced wheat yield and net return. Applying other graminicides at the earliest (two-leaf) stage of wild oat generally resulted in more or similar levels of wild oat fresh weight compared with delayed applications, especially at Saskatoon. With the exception of imazamethabenz, crop yield and net return were unaffected by leaf stage at both locations. The optimal graminicide rate is mostly dependent on the level of wild oat infestation, and the best time to control wild oat is dependent mostly on the particular graminicide.
Nomenclature: CGA 184927 (proposed common name, clodinafop propargyl), 2-propynyl-(R)-2-[4-(5-chloro-3-fluoro-2-pyridyloxy)-phenoxy]-propionate; fenoxaprop-p-ethyl, (±)-2-[4-[(6-chloro-2-benzoxazolyl)oxy]phenoxy]propanoic acid; flamprop-methyl, N-benzoyl-N-(3-chloro-4-fluorophenyl)-DL-alanine; imazamethabenz, (±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-4(and 5)-methylbenzoic acid (3:2); ICIA 0604 (proposed common name, tralkoxydim), 2-[1-(ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-trimethylphenyl)cyclohex-2-enone; wild oat, Avena fatua L. #3 AVEFA; hard red spring wheat, Triticum aestivum L. ‘CDC Makwa’ and ‘CDC Teal.’
Additional index words: Graminicides, leaf stage, application parameters, weed interference, economic return.