The biology of Canadian weeds.: 119.: Cannabis sativa L.

Small, E., Pocock, T. and Cavers, P. B. 2003. The biology of Canadian weeds. 119. Cannabis sativa L. Can. J. Plant Sci. 83: 217-237. Cannabis sativa has been cultivated for millennia in Eurasia and for centuries in North America, as a source of a textile fibre, oilseed, and intoxicating drugs such as marijuana. Considerable literature is available on the agricultural and biological properties of these basic three cultigens, but relatively little is published on wild-growing plants of the species. Most weedy C. sativa differ from the cultigens in a number of ecological properties, particularly with regard to reproductive biology. The species is the classical example of a "camp follower" that is exceptionally adapted to the habitat conditions around settlements: rich, highly manured, moist soils, and open areas resulting from recent removal or disturbance of the vegetation. In Canada, spontaneous populations have been found in all provinces, but forms that have re-evolved wild adaptations are concentrated along the St. Lawrence and lower Great Lakes. The ruderal plants pose a minor weed problem to agriculture but a major problem to law enforcement, and decades of eradication have exterminated many of the naturalized populations in Canada. With the recent re-authorization of hemp cultivation in Canada, it is inevitable that there will be additional escapes and a reinvigoration of the ruderal phase of the species. Mechanical eradication for 2 or 3 yr is effective at destroying populations, and young plants are easily eliminated by herbicide applications.