Nitrogen concentration and application timing affect imazamox efficacy in winter wheat

Field experiments were conducted at four locations in two years in Kansas to determine the effects of urea ammonium nitrate concentrations and application timings on imazamox control of Aegilops cylindrica Host and feral Secale cereale L. in imidazolinone-tolerant winter wheat (Triticum aestivum L.). Based on regression analysis, A. cylindrica was controlled 66–73% with imazamox at 35 g ai. ha−1 plus urea ammonium nitrate at 1–50% v/v. Averaged over urea ammonium nitrate concentrations, fall post-emergence applications of imazamox were 37–45% more efficacious on A. cylindrica than spring post-emergence treatments. Feral S. cereale control increased linearly when imazamox treatments contained urea ammonium nitrate at 1–100%, and fall treatments were more effective than spring treatments at one of two locations. Early applications of imazamox increased wheat yield compared to later applications in two of four experiments, and increased gross profits $69–168 ha−2. However, yields did not differ between imazamox treatments containing different urea ammonium nitrate concentrations at any location.