Wild oat populations resistant to triallate have been identified in Alberta. Dose response experiments were conducted in the greenhouse to determine if triallate-resistant wild oat was controlled by other selective wild oat herbicides. Triallate-resistant wild oat populations were effectively controlled by atrazine, ethalfluralin, fenoxaprop-P, flamprop, imazamethabenz, and tralkoxydim. EPTC and cycloate, which are chemically related to triallate, differed in their efficacy on triallate-resistant wild oats. EPTC at the 0.25x field use rate was more efficacious on triallate-resistant than triallate-susceptible wild oat. In contrast, cycloate at the 0.25 to 0.5x field use rate was less efficacious on triallate-resistant than susceptible wild oats. At higher rates, both EPTC and cycloate killed triallate-resistant wild oat populations. Growers have several herbicide choices to selectively control triallate-resistant wild oat in prairie field crops but should plan to rotate herbicides among different chemical families and adopt integrated weed management practices to reduce the risk of these wild oat populations developing resistance to other wild oat herbicides.

The first occurrences of wild oat resistance to diclofop in the Willamette Valley of Oregon were reported in 1990. Among eight resistant biotypes, GR50 values for diclofop were 3 to 64 times greater than the GR50 for a susceptible wild oat biotype. GR50 values for other aryloxyphenoxypropionate herbicides varied from 1 to over 100 times greater than a susceptible biotype. Only one resistant biotype was resistant to cyclohexanedione herbicides, and this was only a three-fold increase in GR50. Except for one biotype that had a low level of resistance to pronamide, none of the wild oat biotypes were cross-resistant to any other commonly used wild oat herbicide. Levels of resistance and cross-resistance did not follow a consistent pattern among biotypes in this study, suggesting more than one resistance trait. There were significant differences in the light use efficiency, height, dry weight, leaf area, and extent and timing of tillering and flowering of four wild oat biotypes studied. These physiological and morphological differences suggest that these resistant biotypes were selected independently. The diversity of resistance patterns and the coevolution of resistance at several locations will add to the difficulty of resistance management