The Response of Canada Thistle Ecotypes to 2,4-D, Amitrole, and Intensive Cultivation

Abstract

Root sections of Canada thistle (Cirsium arvense (L.) Scop.) ecotypes from different states were field planted at Bozeman, Montana. Canada thistle survival from repeated applications of (2,4-dichlorophenoxy)acetic acid (2,4-D), and 3-amino-1,2,4-triazole (amitrole) was markedly different. Ecotypes varied less markedly to cultivation although they differed significantly. Resistance of ecotypes to cultivation seemed related to adaptation to site while resistance to herbicides apparently was related to inherent physiological differences as well as to differences in adaptation.