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t;anada'1'histle <br />4H /Youth <br />Page 1 of 4 <br />Hortlcutture I Natural Resources I Nutrition Resources I Home <br />no. 3.108 <br />ro IrorJ< <br />Canada Thistle <br />by K.G. Beck 1 <br />Quick Facts... <br />• Canada thistle is a creeping perennial that reproduces from vegetative buds in its <br />root system and from seed. <br />• It is difficult to control because its extensive root system allows it to recover from <br />control attempts. <br />. Combining control methods is the best form of Canada thistle management. <br />• Persistence is imperative so the weed is continually stressed, forcing it to exhaust <br />root nutrient stores and eventually die. <br />Canada thistle (Cirsium arvense) is an <br />aggressive, creeping perennial weed <br />that infests Crops, pastures, <br />rangeland, roadsides and noncrop <br />areas. Generally, infestations start on <br />disturbed ground, including ditch <br />banks, overgrazed pastures, tilled <br />fields or abandoned sites. Canada <br />thistle reduces forage consumption in <br />pastures and rangeland because <br />cattle typically will not graze near <br />infestations. <br />i, •,..tM <br />One plant can colonize an area 3 to 6 ,%~"; ;~-- "' '~ yl Uzi ' ~ <br />feet in diameter in one or two years. `~"~'` ~_ ~'~ ~} <br />Canada thistle grows in a variety of ~' ~~_.,,^,,ll ~1 "' <br />soils and can tolerate up to 2 percent ~ ~f,v„ 4^ '~ ~}- <br />salt content. It is most competitive in ~'`~~' i {' :,y ~ , <br />deep, well-aerated, productive, cool ~~ ~',' 1 <br />soils. It usually occurs in 17- to 35- ~ ` <br />inch annual precipitation zones or <br />where soil moisture is adequate. It is Rgure 1: Canada thistle (Grsium arvense). <br />less common in light, dry soils. A <br />survey conducted in 1998 showed Colorado has about 400,000 acres infested with <br />Canada thistle. <br />Phenology <br />Emergence. Canada thistle develops from seed or vegetative buds in its root system. <br />Horizontal roots may extend 15 feet or more and vertical roots may grow 6 to 15 feet <br />deep. Canada thistle emerges from its root system in mid- to late spring (late April <br />through May) and forms rosettes (Figure 1). <br />http:!/www.ext.colostate.edu/pubs/natres/03108.htmi 6/20/2005 <br />