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​Terrible 10 - Thistles


Bull Thistle
Bull Thistle
Canada Thistle
Canada Thistle

Bull thistle, Canada thistle (Cirsium vulgare, C. avense)

  • Found in open areas, pastures, roadsides.
  • Bull thistle is a biennial, tap-rooted, spreads by seed. First year appears as a rosette and in spring of 2nd year puts up erect, spiny, sparsely haired stems 2-5 ft tall. Leaves are 3-6 in long, pinnate, and hairy on top with cottony white below; leaf lobe tips have stout, sharp needles. Fragrant purple/pink flowers are supported by a bulbous, spine-covered bract.
  • Canada thistle is a perennial, spreads by rhizome and seed; it does not have hairy leaves and the bract below the flower of Canada thistle lacks spines. Canada thistle is not tap-rooted, has spreading rhizomes.
  • Bull thistle is Eurasian, arrived in contaminated seed.
  • The sharp spines on these thistles deter animals from grazing; when established in hay fields they have a serious economic impact on value of the hay.