Weed of the Month: Musk Thistle

Weed of the Month: Musk Thistle

Musk Thistle

Photo: Photos.com

Common name: Musk thistle
Other names: Nodding thistle
Scientific name: Carduus nutans L.

Life Cycle: Biennial; sometimes annual
Origin: Eurasia
Poisonous: No

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
Musk Thistle
Musk Thistle

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.

Want more articles like this? Sign up for the Bluegrass Equine Digest e-Newsletter.

More information on Gluck Equine Research Center and UK Ag Equine Programs.

Stay on top of the most recent Horse Health news with FREE weekly newsletters from TheHorse.com. Learn More