THE BIOLOGY OF CANADIAN WEEDS.: 89. Carduus nutans L. and Carduus acanthoides L.

Abstract

Carduus nutans L. and C. acanthoides L. are introduced weeds, primarily of roadsides, fields and pasturelands. Both species occur in eastern and western Canada with C. nutans more common than C. acanthoides in western Canada. High seed production and germination rate on open soil contribute to the success of the species as weeds, as do the spiny leaves and stems which deter grazing by animals. Mowing or the application of hormone-like herbicides are both effective means of control. Biological control methods have also been used for both species, but have been most successful in the control of C. nutans.Key words: Musk thistle, nodding thistle, plumeless thistle, Carduus spp.