Field experiments were conducted at five locations in Kansas, Nebraska, and Wyoming to determine the effects of imazamox rate and application timing on winter annual grass control and crop response in imidazolinone-tolerant winter wheat. Imazamox at 35, 44, or 53 g ai/ha applied early-fall postemergence (EFP), late-fall postemergence, early-spring postemergence (ESP), or late-spring postemergence (LSP) controlled jointed goatgrass at least 95% in all experiments. Feral rye control with imazamox was 95 to 99%, regardless of rate or application timing at Hays, KS, in 2001. Feral rye control at Sidney, NE, and Torrington, WY, was highest (78 to 85%) with imazamox at 44 or 53 g/ha. At Sidney and Torrington, feral rye control was greatest when imazamox was applied EFP. Imazamox stunted wheat <10% in two experiments at Torrington, but EFP or LSP herbicide treatments in the Sidney experiment and ESP or LSP treatments in two Hays experiments caused moderate (12 to 34%) wheat injury. Wheat injury increased as imazamox rate increased. Wheat receiving imazamox LSP yielded less grain than wheat treated at other application timings in each Hays experiment and at Sidney in 2001. No yield differences occurred in one Torrington experiment. However, yields generally decreased as imazamox application timing was delayed in the other Torrington experiment. Generally, imazamox applied in the fall provided the greatest weed control, caused the least wheat injury, and maximized wheat yield.
Nomenclature: Imazamox; feral rye, Secale cereale L. #3 SECCE; jointed goatgrass, Aegilops cylindrica Host # AEGCY; wheat, Triticum aestivum L. ‘CO980875’.
Additional index words: Central Great Plains, herbicide-tolerant wheat, IMI-wheat.
Abbreviations: EFP, early-fall postemergence; ESP, early-spring postemergence; KS-A, Hays, KS, experiment A; KS-B, Hays, KS, experiment B; LFP, late-fall postemergence; LSP, late-spring postemergence; MSO, methylated seed oil; NE, Sidney, NE; UAN, urea ammonium nitrate; WY-A, Torrington, WY, experiment A; WY-B, Torrington, WY, experiment B.