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- • • ~ ~;~',1~V1CJe ~ Urrlverslty ~_ Cooperati~ Extension 7 no. s.108 r- ._ r :- Canada thistle: biologp and management in pastures and rangeland 'K. George Beck Buick Facts Canada thistle >s a c~eeptng perenmial that iepno- daces from vegetative buds 1n its root system and f~ seed. It Ls very di®cult to corJirol because Its extensive roct system has vast nutrierrt stores that allow tt to recover hlom control attempts. Combmmg contrd methods >s the best form oC Canada thistle management Persistence >n corthnl efforts 15 >arperatlve so the weed >s corttinuaIly stressed. fordrJg it to exhaust root nutricrlt stores and eventually die. Canada thistle is an aggressive, creeping peren- nial weed that Infests crops, Pastures. rangeland. roadsides, and rwn~rop areas. It 1s a weed of 27 crops !n 37 countries, worldwide. Generally, urfesta- Uons start on disturbed ground including ditch banks, overgrazed pastures, tilled fields, or open waste places. Canada thistle reduces forage con- sumption >n pastures and rangeland because cattle will not graze near infestations. One plant can colonize an area 3 feet to 6 feet in diameter >n one or two years. Canada UrisUe 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 soils. Canada thistle usually occurs in 17-inch to 35-inch annual precipitation zones or where soil moisture >s adequate. It is less common In light. dry soils. Phenology Emergence. Canada thistle develops from seed or vegetative buds 1n !ts root system. Hortzorital roots may extend 15 feet or more and vertical roots may grow 6-feet to 15-feet deep. Canada UrisUe emerges from its root system !n middle to late spring (late April Uuough May) and forms rosettes.'Ihe greatest .`~' D flush of rootderived plants occurs !n spring, but another flush occurs >n fall. A flush can occur any- time during the growing season when moisture !s adequate.'Ihis >s particularly a problem when Canada thlstie growth >s disturbed by tlllage or herblcydes. This faMor of Canada UrisUe's biology car be manipulated to the land manager's advantage. Plants Urat germinate from seed do so at about th same time as root-derived shoots. Seedltngg grow slowly and are senslttve to competition, particularly i shaded. Canada UrisUe seedlings develop a perennial habit, the ability to reproduce for their root systems, at seven to etgart weeks of age. Reproduction and spread. Canada thistle begirt to flower in late spring to early summer (mid June through July) >n response to 18-hour days. Plants ar either male or female (dioecious) and grow !n GrculaJ patches that often are one clone and sex. Female flowers produce a sweet odor and insects readily pollinate d1H'erent sexed patches up to 200 feet apart Canada thistle develops seed sparingly. It may pro- duce 1000 to 1500 seeds per plant. Generally. vegetative reproduction from tts root system rnntrlb- utes to kJCal spread and seed to long dlstarrce dis- posal. Seed maybe transported long distances by 1K Ce,orge Beck Cdando State Chih~aslty Coopr3at4Je F.~erlslan uJeod sclerur: specYalist mid assaclafe projessn ptantpatlrator,/y mid uJeed sctencr (7/911 mC,obrado State [hW.~rsthJ Caopaatlue F.Idertsbn. 1991. Issued in funhcnna of Coopendve Extension work, Ans of May 8 and Junc b. 191 ~. In snopcradon with me U.S. Dcpanmcnt o! Agrlculturc. Kcnncrh R. Holcn. dimctor of CDOpcntivc Extension. Colondo Sntc University. Fon Collins, Colondo. Coopentlve Extension Drograms are avadablc [o all wlthou[ discrimination. To simDlily t¢hniul tcrminDlogy, axle names of Draducu and epul0mcm ocuslo[Wly will be usW No cndorscmcnt of Draduca named Is in[<ndcd nor Is cri[F cism ImWiod o/ Droducrs nat men[loned.