musk thistle flower head

Musk thistle (Carduus nutans)

Herbaceous biennial. Plants overwinter as rosettes in the first year and bloom in the second year. Flowering plants are 1-7’ tall. Musk thistle has a multi-branched stem that appears winged.

Overview

Regulated areas of musk thistle
Musk thistle is Restricted (Orange counties)

Other names for this plant include:

  • Common names: nodding thistle
  • Scientific names: C. macrocephalus; C. nutans spp. macrocephalus; C. nutans ssp. leiophyllus

Ecological threat:

  • Invade areas such as pastures, old fields, roadsides, waste areas, ditch banks, and prairies.
  • When in meadows and pastures, grazing animals avoid musk thistle and focus on native plants giving the invasive the upper hand.

Classification in Wisconsin: Restricted

Species Assessment Groups (SAG) were assembled to recommend a legal classification for each species considered for NR 40. The recommendation for musk thistle was based upon this literature review developed by the department.

Identification

First year plants-Leaves: Basal leaves are up to 12-17” long, lance-shaped-oblong and lobed with spiny margins.

Second year plants-Leaves: Alternate leaves clasp the stem giving it a winged appearance. They are coarsely lobed with prominent terminal spine and slightly wavy yet smooth and hairless on both sides and are dark green with light green midribs and a white margin.

Flowers: Musk thistle has large red to purple, solitary, terminal flowerheads, 1.5-3” across, and usually bent over or “nodding”. Bloom May through August.

Fruits & seeds: A single flowerhead can produce up to 1,200 seeds that are viable for over 10 years. Wind-dispersed seeds can travel long distances.

Roots: Single taproot.

Similar species:Native marsh thistle (Cirsium muticum) has non-spiny stems and flower heads. Canada thistle (Cirsium arvense; invasive) does not have a winged stem or spines on it stem or flower heads. Bull thistle (Cirsium vulgare; non-native) has prickly winged stems and leaves have prickly hair above, with white wooly hair below. The single or clustered purple flowers, 1.5-2” across, are borne at the ends of branches and are enclosed by narrow, spine-tipped bracts.

Distribution

Known county distribution of musk thistle
Counties in WI where musk thistle has been reported (as of July 2011). Both vouchered and unvouchered reports included

Do you have musk thistle in your county but it isn't shaded on the map? Send us a report.

Control

Mechanical: Sever root 1-2” below the soil surface. Repeated mowing (minimum 2-3 times per growing season) when flower buds are about to open will prevent seed production.

Chemical: Applications are most effective when plants are in the rosette stage. Foliar spray with glyphosate during bolting phase when plants are 6-10” tall, during the bud to flower phase, or rosettes in the fall. Can also apply a foliar spray with clopyralid or metasulfuron-methyl. For musk thistle on severely disturbed sites, apply of 2, 4-D ester or dicamba in early bolting phase. Or apply in combination – dicamba with 2, 4-D ester.

Biological: Musk thistle- flower head weevil (Rhinocyllus conicus) and the rosette weevil (Trichosirocalus horridus), released in some states but not Wisconsin due to risks presented to rare native thistles.

Photos

View musk thistle pictures in our photo gallery!

Resources

Sources for content:

  • Czarapata, Elizabeth; Invasive Plants of the Upper Midwest: an illustrated guide to their identification and control. University of Wisconsin Press. 2005. Pg. 101-102
  • Gassmann A. and L.T. Kok. Musk thistle In: Van Driesche, R., et al., 2002, Biological Control of Invasive Plants in the Eastern United States, USDA Forest Service Publication FHTET-2002-04, 413 p [exit DNR]. Last updated Nov. 5, 2003.

Links for More Information

Last revised: Wednesday December 19 2012