Publication Date


Advisor(s) - Committee Chair

Elmer Gray, W.B. Stroube, L.D. Brown, Wilbert Normand

Degree Program

Department of Agriculture

Degree Type

Master of Science


Carduus nutans L., commonly called nodding thistle or musk thistle, has been in the United States for over 50 years; however, it was not until the early 1940's that it was identified in Kentucky. It was first identified in Kentucky in Warren County, and by 1970 had spread to 88 of the 120 counties in Kentucky. The thistle is present in all regions of the state, but most of the counties not having the thistle are located in the mountainous region of Eastern Kentucky.

The thistle plant has a fleshy tap-root which is characteristically hollow near the soil surface. Flowering is determinate and the flowers vary in color from a deep pink at opening to near white at maturity. The plant is a prolific seed producer and may grow to a height of over eight feet in favorable growing conditions.

In Central Kentucky, nodding thistle seeds are disseminated from June through August. The seeds are about three millimeters long and vary in color from gray to straw-brown at maturity. There appears to be a minimum eight-week dormancy period before the seeds will germinate. Ninety percent germination was obtained using one-year-old seeds. After emergence, plants enter the rosette stage in which they over-winter. Rosettes may reach four feet in diameter prior to bolting. Bolting occurs between March and August, and flowering begins in mid-May and continues through August. Nodding thistle plants in the study produced up to 561 heads per plant, and up to 1200 seeds per head. Individual plants produced from 200 to over 160,000 seeds. Nodding thistle plants in Central Kentucky may act as summer annuals, winter annuals, or biennials.


Agriculture | Life Sciences | Plant Sciences | Weed Science