Defining optimum herbicide rates and timing for wild oat (Avena fatua) control in spring wheat (Triticum aestivum)

Knowledge of optimal combinations of graminicide rate and stage of applicat ion could improve the effectiveness and net benefit of commonly used gramin icides. A study was conducted at two locations in Saskatchewan, Canada, fro m 1994 to 1997. Factorial combinations of five graminicides (CGA 184927, fe noxaprop-p-ethyl, ICIA 0604, imazamethabenz, and flamprop-methyl), three gr aminicide rates (full, two-thirds, and one-third recommended label rate), a nd three leaf stages of wild oat (Avena fatua; two-, four-, and six-leaf) w ere compared to determine their effect on wild oat fresh weight, wheat (Tri ticum aestivum) seed yield, and net return. Wild oat fresh weight increased and wheat seed yield decreased to a greater extent at Saskatoon (median wi ld oat fresh weight of 56 g/m(2)) than at Scott (median wild oat fresh weig ht of 85 g/m(2)) when graminicide rate was reduced from the recommended lab el 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 lat er growth stages caused greater wild oat fresh weight at both locations and reduced wheat yield and net return. Applying other graminicides at the ear liest (two-leaf) stage of wild oat generally resulted in more or similar le vels of wild oat fresh weight compared with delayed applications, especiall y at Saskatoon. With the exception of imazamethabenz, crop yield and net re turn were unaffected by leaf stage at both locations. The optimal graminici de rate is mostly dependent on the level of wild oat infestation, and the b est time to control wild oat is dependent mostly on the particular graminic ide.