Musk Thistle
(Carduus nutans L.)
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MATURE PLANT
* 5-8 feet tall |
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ROSETTE
* leaves evenly lobed and spiked |
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FLOWER
* 2-3 inch diameter lavender color |
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INFESTATION
* approx…936 acres in El Paso County | |
Musk Thistle, (Carduus nutans L.) also known as the nodding thistle. It is a member of the Aster family, Thistle tribe. The Musk Thistle is a biennial that reproduces only from seed. The first year it produces a large, compact rosette from a large, fleshy, corky taproot that is hollow near the ground surface. The second year produces a spiny erect stem that extends, 2 to 7 feet tall and branches at the top. The leaves are shiny, long dark-green with a light green midrib and mostly white margins and very sharply lobed, with stickers. The flower is a large 2" to 3" broad pink to lavender blossom that is surrounded by numerous, lance-shaped, spine-tipped bracts. The plant blooms in June or July. The seeds are straw-colored and oblong that can be in excess of 20,000 per plant. In which 90% of the seeds may germinate in the first year or two. The seeds may be viable for at least 10 years in the soil.
Keep from seeding. Dig, mow, spray or pull. Mowing alone is only effective if done each week over several growing seasons. Tilling is not a recommended control because it will break up the roots and stimulate new plants from the root and shoot pieces. Small roots can survive 100 days without photosynthesis. Plant perennial grasses in the fall.
A beetle, Rhinocyllus conicus, the larvae of which eat the seed, has made a serious decline in this plant population. Allow the beetle to work, but do not let the late season blossoms mature.