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Scotch Thistle Identification and Management spine-tipped bracts curve away from the flowering head. The flower receptacle x is fleshy and has pits to hold seeds.The ` r plants flower from mid-June to Septem- fY, ber. Scotch thistle seeds have the abilityt to mature in flower buds and heads that have been removed from the stalk. Both V"'t species can produce up to 14,000 seedsper plant. Seeds remain viable for up to '';' 30 years but germinate readily with mois- ture in spring and fall. C cotch thistle invades rangeland, over- p t<y � Jgrazed pastures, roadsides, and irriga- tion ditches. Both species prefer moist soil, such as areas adjacent to creeks and C) Scotch thistle includes two species, rivers. Roadsides appear to be espe- /� Q,• Onopordum acanthium L. and O. tauricum Willd. Both are non-native cially vulnerable to invasion likely due C, ll; Meh*hcff,Jni, tyofQ to the water runoff from the shoulders. biennial fortis. During the first year of Maintaining healthy pastures and na- _ growth, both species appear as a rosette tive plants, minimizing soil disturbance, in spring or fall. During the second year in mid to late spring the stems bolt, the changing land use practices to prevent .". overuse, and using seed-free equip- plants flower, set seed, and the plants �. ment are critical measures to preventing die. Both Scotch thistle species can grow infestations. As with most biennials, once r up to 12 feet tall and basal rosettes can be up to 2 feet in diameter. Stems are established, limiting seed production is = ,, critical to effective control. Due to the numerous and branched. Characteristi- n Sonnie Mi"iOn,NPS robust, spiny nature of Scotch thistle, {— cally, the entire length of stems from this plant can act as a living barbed wire n� both species have broad wings with spiny fence, making areas impassible for wild- (,("1j" tips. O. acanthium leaves have an overall life, livestock, and people and unpalat- ' gray color from dense woolly hairs. O. able to cattle. tauricum leaves are glandular and not as Q C=� hairy as O. acanthium. For both, leaves ` QQ_ are spiny. Both species have a distinct To control seed production, plants with I mid-rib. Flower heads are terminal, violet buds or flowers should be collected, bagged and immediately disposed of or to reddish in color, 1 to 3 inches in diam- eter, and arranged in a raceme. One plant "t destroyed. Chemical control is most ef- 6on"w%r%"PS L� �can produce up to 100 flower heads.The fective when plants are in rosette stage, '(v spring or early fall. Mechanical controls �f can be used to eliminate 2015 Quarter Quad Survey small patches or plants in a Key iD Point s Scotch Thistle zm ooarcerwae F�m sire,cac� +cn° � .:ev later growth stage. Pitted1. e �• c�snwo°o n coaado on .ream ac m—, flower •,� "�;9, Scotch thistle is clesignat receptacle. • Jed as a "List B" species °aa•� •° , ,� 2. Prominent mid- in the Colorado Noxious Weed Act. It is required to be eradicated; some popula 3. Wide lobed - Fa. tions may be contained or leaves with suppressed depending on distinct mid rib. Ra- state regulations. For state regulations described for 4.Wide spiny wings extend each county, refer to the the length of most recent Rule, or visit the stem. www.colorado.gov/ag/co- weedcontacts� .e, _„�•<am�.°°°"' "°°"'R"'•"- weedcontacts for details.