THE BIOLOGY OF CANADIAN WEEDS .100. LYTHRUM-SALICARIA

Lythrum salicaria is a serious weed of wetlands in Canada, particularly in Ontario and Quebec. Indeed some assessments suggest that this exotic is now responsible for the conversion of more wetland habitat than is current human development pressure! Lythrum is a heterostylous species and clones by means of root buds. Despite its tristylous breeding system, Lythrum is a successful colonizer. and can produce prodigious numbers of seeds. It is likely that control can be achieved by hand-pulling in low-density populations, but once the species is established it generally becomes abundant and often approaches a monoculture. This species is particularly difficult to control because of its strong competitive ability, the extreme sensitivity of wetland habitats, and the likelihood of serious repercussions for wetland wildlife and fisheries if herbicides are used to control it. We see better possibilities for control through cultural techniques (e.g., manipulation of water levels to favour native species), enhancement of North American herbivores, and. possibly, the introduction of biological control agents from Europe and Asia.