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Bull Thistle Identification and Management <br /> like white hairs. Seeds remain viable for , xa <br /> approximately three years. Mature plants <br /> can produce up to 4,000 seeds per plant . <br /> Bull thistle generally needs soil tempera- <br /> ture between 50' and 80'F, moisture and <br /> canopy gaps to germinate seeds. r :, <br /> L k <br /> Bull thistle invades dry to moist en- ' <br /> vironments. It prefers nitrogen-rich "' <br /> soils, and it grows on gravelly to clay-tex- <br /> tured soils It thrives in areas such as pas- <br /> tures, overgrazed rangeland, roadsides, <br /> and logged areas. Bull thistle infestations <br /> are heaviest in the northwestern portion <br /> ow„aeiant: "� r of Colorado. It is widespread throughout <br /> Bull thistle, Cirsium vulgare(Savi)Ten., the United States and parts of Canada. <br /> is a biennial forb that was introduced <br /> to North America as a seed contaminant. <br /> eavy infestations reduce livestock g^KeAdAey,>HReteumvest;y__ <br /> Flowers are in a raceme arrangement. H forage.The presence of bull thistle n <br /> in hay decreases the forage value and <br /> The gumdrop-shaped disk flowers are �; 'Z <br /> pinkish to dark purple in color and 1 lowers the market price. It is an ag- LA <br /> to 2 inches in diameter. The pappus <br /> gressive weed, but it will not withstand �• <br /> has feather-like bristles;the receptacle cultivation. Bull thistle is often a transient <br /> is densely bristly. The flower bracts are species, appearing in recently disturbed '~. , <br /> somewhat tapered and covered with areas and becoming a dominant species <br /> spines 2-5 mm long. Leaves are alternate for several years if left untreated. It can <br /> with deeply lobed margins that are spiny. cause hay fever in some individuals. i 0 Ste"Dewey,U[SWe UnWerbitr, � <br /> In mature plants the base of the leaves <br /> clasp the stem and extend down the stem n /� aintaining healthy pastures and �CJJ <br /> to the lower node.The plant has one 'V' rangeland, guarding against disturILA <br /> - <br /> short, fleshy taproot with several lateral bance or overuse is the best prevention <br /> ffec- <br /> measure against bull thistle. As with <br /> roots.There is debate about the e <br /> II thistle; most biennials, limiting seed production <br /> effec- <br /> tiveness of self-pollination in bull <br /> P <br /> outcrossing though pollination produces is critical to effective control. Chemical <br /> an abundance of viable seed. Flower buds control is the most effective and efficient <br /> and heads that are removed from the method of eradication if applied during 3 �� <br /> stalk can still mature and become viable. the rosette stage, spring or early fall. <br /> Seeds are capped with a circle of plume- To reduce seed production, plants with <br /> buds or flowers should be collected and <br /> 2015 Quarter Quad Survey bagged, disposed of or de- Points <br /> stroyed. Mechanical control, <br /> Bull Thistle 20150uaWMad Feu SaveY OatsFlowers <br /> Grswm vul a,e ameba,v,Co°m"• such as pulling, has limited <br /> arranged in a <br /> effectiveness. <br /> flower <br /> a«e :!!d is gum-drop <br /> aaa• ull thistle is designated shaped. <br /> awm �• <br /> as a "List B" species in <br /> leaves <br /> the Colorado Noxious Weed - • <br /> i. <br /> Act. It is required to beclasp the stem <br /> eradicated; some popula- & extend •• <br /> wn <br /> tions may be contained or the stemto <br /> •p- suppressed depending on •de •_ • <br /> � • ,,,�, -- _ state regulations. For state •• surface of <br /> regulations described for leaves have <br /> ����.•. each county, refer to the stiff, rough <br /> most recent Rule, or visit hairs <br /> www.colorado.gov/ap,/co- <br /> weedcontacts weedcontacts for details. <br />