Kegode, G. O. and Darbyshire, S. J. 2013. The Biology of Canadian Weeds. 152. Artemisia biennis Willd. Can. J. Plant Sci. 93: 643–658. Artemisia biennis Willd. (biennial wormwood, armoise bisannuelle) is an annual or biennial species native to western North America. Closely related species occur in Eurasia and South America which are sometimes considered conspecific. Spreading elsewhere in North America occurred along transportation corridors soon after European settlement and it has since been introduced to other parts of the world. As an economically important weed its impact appears to be increasing, possibly due in part to reduced tillage practices. The most significantly affected regions are the Prairie Provinces of Canada and the northern Great Plains in the United States. Many cereal, oilseed, pulse, vegetable and forage crops are affected where it can reduce yields at relatively low densities. A wide range of soil and moisture conditions are tolerated and it can form dense populations in disturbed habitats where its competitive ability is enhanced by prolific seed production, indeterminate seedling emergence and allelopathic effects. Although tolerant of a number of herbicides in different classes, good control can be achieved through careful timing and split application strategies.