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i,anaaa tensue Y i?:.A:?Jy11?J AktAW yllIdo *V VD Went tir,V A V. T 4-H /Youth Agriculture Famlty2onsumer Horticulture Natural Resources Nutrition Resources Home no. 3.108 Canada Thistle by K.G. Beck 1 Quick Facts... • Canada thistle is a creeping perennial that reproduces from vegetative buds in its root system and from seed. • It is difficult to control because its extensive root system allows it to recover from control attempts. • Combining control methods is the best form of Canada thistle management. • Persistence is Imperative so the weed is continually stressed, forcing it to exhaust root nutrient stores and eventually die. Canada thistle (Cirsium arvense) is an aggressive, creeping perennial weed that infests Crops, pastures, rangeland, roadsides and noncrop areas. Generally, infestations start on disturbed ground, including ditch banks, overgrazed pastures, tilled fields or abandoned sites. Canada thistle reduces forage consumption in pastures and rangeland because cattle typically will not graze near infestations. One plant can colonize an area 3 to 6 feet in diameter in one or two years. Canada thistle grows in a variety of soils and can tolerate up to 2 percent salt content. It is most competitive in deep, well-aerated, productive, cool -s soils. It usually occurs in 17- to 35- inch annual precipitation zones or where soil moisture is adequate. It is Figure 1: Canada thistle (OrVurn arvense). less common. in, light, dry soils. A survey conducted in 1998 showed Colorado has about 400,000 acres infested with Canada thistle. Phenology Emergence. Canada thistle develops from seed or vegetative buds in its root system. Horizontal roots may extend 15 feet or more and vertical roots may grow 6 to 15 feet deep. Canada thistle emerges from its root system in mid- to late spring (late April through May) and forms rosettes (Figure 1). http://www.ext.colostate.edu/pub-,/natres/03108.htmi 6/20/2005