2012. The Biology of Canadian weeds. 150 Erechtites hieraciifolius (L.) Raf. ex DC. Can. J. Plant Sci. 92: 729Á746.Erechtites hieraciifolius, American burnweed, is a herbaceous annual in the Asteraceae native to forest zones of eastern North America, but introduced to parts of Europe and the Pacific region. Confusion sometimes arises in distinguishing it from other weedy rayless composites in Canada, such as Senecio vulgaris (common groundsel) and Conyza canadensis (Canada fleabane). A pioneer therophyte species of forest zones, it occurs in large numbers when associated with major disturbances such as forest fires, but is also common in areas of smaller scale disturbance such as shores, forest edges and wind-throws. Soil conditions may vary greatly in nutrient content, moisture content, pH and salinity. In Canada, it is generally considered a minor garden and agricultural weed. It is most common in crops such as lowbush blueberry (Vaccinium spp.), cranberry (Vaccinium macrocarpon), strawberry (Fragaria)ananassa) and vegetable crops; however, it occasionally occurs in other field and forage crops. Impacts include a variety of problems contributing to increased production costs or crop yield losses, including herbicide resistance, resource competition, and as a reservoir harbouring crop pathogens. It has been valued as a medicinal herb for treating a variety of ailments. Populations may grow rapidly in response to disturbances typical of managed landscapes, but E. hieraciifolius can usually be effectively controlled by chemical, cultural or manual weed control tactics.Darbyshire, S. J., Francis, A., DiTommaso, A. et Clements, D. R. 2012. La biologie des mauvaises herbes au Canada. 150 Erechtites hieraciifolius (L.) Raf. ex DC. Can. J. Plant Sci. 92: 729Á746. L'e´rechtite a`feuilles d'e´pervie`re (Erechtites hieraciifolius) est une herbace´e annuelle de la famille des Aste´race´es indige`ne aux re´gions forestie`res de l'est de l'Ame´rique du Nord, mais qui a e´te´introduite dans certaines parties de l'Europe et du Pacifique. On la confond parfois a`d'autres adventices a`rayons courts de la famille des Compose´es qui poussent au Canada tels le se´nec¸on vulgaire (Senecio vulgaris) et la vergette du Canada (Conyza canadensis). Espe`ce pionnie`re the´rophyte, on en retrouve de grand peuplements aux endroits qui ont subi de profondes perturbations comme un feu de foreˆt, cependant l'espe`ce colonise souvent des zones plus restreintes comme les rivages, la lisie`re des boise´s et les chablis. Les conditions du sol peuvent varier conside´rablement quant a`la concentration d'e´le´ments nutritifs, la teneur en eau, le pH et la salinite´. Au Canada, on la conside`re ge´ne´ralement comme une adventice secondaire dans les jardins et les champs. L'e´rechtite a`feuilles d'e´pervie`re se rencontre le plus souvent dans les cultures comme le bleuet nain (Vaccinium spp.), la canneberge (Vaccinium macrocarpon), la fraise (Fragaria)ananassa) et les plantes maraıˆche`res, cependant, on la de´couvre a`l'occasion dans d'autres grandes ...