Field performance of imazamox-resistant spring wheat

Abstract

The imidazolinone herbicides possess high biological potency at low application rates, and are an attractive alternative for weed control in spring wheat (Triticum aestivum L.). Four mutation-derived spring wheat lines resistant to the imidazolinone class of herbicides were evaluated in field trials to investigate the levels of resistance to imazamox. Imazamox was applied post-emergence at 0 g (hand-weeded control; HWC) 20 g, 40 g, 80 g and 160 g active ingredient (a.i.) ha-1. A standard herbicide treatment (SHT; clodinafoppropargyl, bromoxynil and MCPA ester) representing a common herbicide application to spring wheat in western Canada was also included. The cultivar CDC Teal was included as a susceptible control. At 160 g ha-1, imazamox reduced yield in lines with a single resistance gene (TealIMI 10A, TealIMI 11A, and BW755) by up to 43% and delayed maturity up to 13 d. TealIMI 15A, the only line evaluated with two resistance genes, was the most resistant of all lines, with no significant increases in days to spike emergence (DSE), days to physiological maturity (DPM), and no reduction in yield at the highest rate of imazamox. The susceptible control was killed within 2 wk of imazamox application, regardless of application rate. These results indicate that two resistance genes are preferable for ensuring satisfactory levels of resistance to the formulation of imazamox used in these studies.