Weed of the Month: Musk Thistle
By University of Kentucky's College of Agriculture, Food, and Environment • Feb 22, 2014 • Article #23651
Common name: Musk thistle
Other names: Nodding thistle
Scientific name: Carduus nutans L.
Life Cycle: Biennial; sometimes annual
Musk thistle, also known as nodding thistle in some areas, is distributed across the United States and is listed as noxious in many states. This invasive species can reach heights of 6 feet and grows in pastures, rangeland, and along roadsides. Its light windborne seeds can move great distances to infest adjacent areas. One of this plant's only redeeming qualities is its bright red to purple flowers that bloom from May to September.
Musk Thistle as a seedling (top), a rosette (middle), and a flower (bottom).
Seeds germinate in the fall or spring and form rosettes. Generally, the flowering plants are 2 years old, although some plants act as annuals and produce seeds after one year of growth. Controlling musk thistle in pastures is relatively easy with herbicides that kill the thistle yet do not harm pasture grasses. Consult your local Cooperative Extension Service agent for a list of herbicidal controls in your area. Mowing is only effective if done after the stem elongates but before seed heads are produced. Thistlehead weevil larvae eat this thistle's seeds and are an effective biological control in some areas of the United States.
William W. Witt is a retired professor and researcher in the University of Kentucky College of Agriculture’s Plant and Soil Science Department.
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