Beckie, H. J., Johnson, E. N., Leeson, J. Y., Shirriff, S. W. and Kapiniak, A. 2014. Selection and evolution of acetyl-CoA carboxylase (ACC)-inhibitor resistance in wild oat (Avena fatua L.) in a long-term alternative cropping systems study. Can. J. Plant Sci. 94: 727-731. In 2012, 18 yr after experiment establishment, wild oat from the spring wheat phase of seven of nine alternative cropping systems (each of three input levels applied to three levels of cropping diversity) were sampled and screened for ACC-inhibitor resistance. The frequency or level of resistance in wild oat was greatest in the diversified annual grains systems (42-60% of individuals), and lowest in the diversified annual perennial systems (<3%). The results of this study demonstrate the importance of perennial crops in slowing the selection and evolution of resistance in this weed. Moreover, annual cropping system diversity by itself is not enough to slow the evolution of ACC-inhibitor resistance in wild oat; cropping diversity must be linked with herbicide mode-of-action diversity and herbicide-use reduction.