Chemical Control of Canada Thistle

Abstract

Field studies were conducted to evaluate the effectiveness of one, two, and three annual applications of atrazine [2-chloro4-(ethylamino) -6-(isopropylamino)-s-triazine], 2,4-D [(2,4-dichlorophenoxy) acetic acid], dicamba (3,6-dichloro-oanisic acid), and a three way mix of dicamba, mecoprop [2-4(4-chloro-o-tolyl) oxyl propionic acid], and 2,4-D at a ratio of 7:5:20 at different stages of development for the control of Canada thistle [Cirsium arvense (L.) Scop.]. Two consecutive annual applications in all atrazine treatments achieved the same level of control as cultivation every 5 weeks. In the year of the last treatment, Canada thistle was controlled with two or more consecutive annual applications of the hormonetype herbicides (2,4-D, dicamba, and the three way mix); however, in the year following the last treatment, regrowth occurred