Scotch thistle Onopordum acanthium L

Key identifying traits

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  Very large thistle growing up to 8 feet tall
  
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  Stems have broad spiny wings
  
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  Leaves are spiny and covered with fine dense hair
  
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  Hairy leaf surface causes a grayish appearance
  
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  Flower heads numerous, 1 to 2 inches in diameter
  
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  Flowers violet to reddish; bracts taper to a spine
  
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  Upper leaves alternate and coarsely lobed
  
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  Basal leaves up to 2 feet long and 1 foot wide
  

Biology and ecology

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  Tap-rooted biennial that reproduces by seed
  
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  Invades roadsides, range and disturbed areas
  
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  Thrives in sunny sites – but can tolerate shade
  
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  Up to 50,000 seeds per plant; seeds viable 6-15 years
  
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  Repeated branching may result in plants 5’ wide
  
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  Dense stands can create barriers that restrict livestock
  
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  Drought tolerant but can flourish along open streams
  

Control

Chemical – Several effective at label rates; best timing is in early spring when plants are in rosette stage and again in fall when more rosettes germinate

Where found- Scattered small infestations, particularly in old barnyards as well as some sites covering several acres over pasture/range ground in the northern half of the county.