Beckie, H. J., Francis, A. and Hall, L. M. 2012. The Biology of Canadian Weeds. 27.Avena fatuaL. (Updated). Can. J. Plant Sci. 92: 1329-1357. An updated review of biological information is provided for Avena fatua. A widespread species originating in Eurasia, A. fatua is one of the 10 worst annual weeds of temperate agricultural regions of the world. Key weediness traits of this highly selfing species include fecundity, seed shatter, and a large and persistent seed bank with variable degrees of primary seed dormancy. The species occurs in all Canadian provinces and most states in the USA. In Canada, it is most troublesome as a weed in the prairies, where it has spread throughout crop areas in all climatic zones. Depending upon plant density and relative time of emergence, A. fatua competition may reduce annual crop yields by as much as 70%. First cohort emergence of A. fatua coincides with planting and emergence of spring-seeded crops, although additional cohorts can emerge throughout the growing season. Avena fatua is more abundant in zero-than intensive-tillage systems; the former regime promotes earlier and greater emergence because of a shallower and less persistent seed bank. Despite the introduction of highly efficacious herbicides in the 1970s and 1980s, abundance of the species has not declined across the Canadian prairies or elsewhere. The continual evolution of herbicide-resistant A. fatua populations, seed spread via farm machinery, and limited herbicide modes of action for its control threaten sustained annual field crop production in many temperate agricultural areas. Further adoption and integration of multiple non-herbicidal weed management practices, such as enhanced crop seeding rate, competitive crops and cultivars, and precision fertilizer placement, should help mitigate A. fatua interference. The species has some beneficial uses as an alternative feed and food constituent or industrial feedstock, as well as potential in cultivated oat (Avena sativa L.) improvement.