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Plumeless thistle

(Carduus acanthoides)

Photo of plumeless thistle
Photo credit: Emmet J. Judziewicz

Large herbaceous biennial. When the plant bolts in the second year it can be three to six feet tall. Stems are freely branching and have leaf-like spines.

Overview

Other names for this plant 
  • Common names: spiny plumeless thistle, welted thistle
Ecological threat
  • Infest low-quality areas first, such as roadsides, disturbed areas, ditch banks and old fields. Spreads into high-quality prairies.
  • When in meadows and pastures, grazing animals avoid plumeless thistle and focus on native plants giving the invasive the upper hand.
Overview map of plumeless thistle classification in WI
Restricted (orange) counties

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 plumeless thistle was based upon this literature review [PDF] developed by the department.

Identification

First-year plants-leaves: First-year rosette leaves are up to two inches long, deeply divided with lobes ending with spines.

Second-year plants-Leaves: Dark green with light green midrib and hairy on the underside; leaves are deeply divided with lobes ending in a spine.

Flowers: Red-purple flowers singly or in clusters. Flower heads are up to one inch in diameter.

Fruits & seeds: Up to 10,000 seeds per plant with seeds disperse within seven to 10 days of flowering. Seeds are viable in the soil for more than 10 years.

Roots: Single taproot.

Similar species: Musk thistle (Carduus nutans) is very similar except for the solitary flower is much larger, 1 1/2 to three inches wide and slightly nodding. The leaves are also hairless on both sides.

Control

Mechanical: Close mowing of second-year plants twice per growing season just before flowering. Cut or mow at early bud both times. Cut plants with a sharp shovel one to two inches below soil surface before flowering.

Chemical: Spot spray rosettes in fall with 2, 4-D ester; foliar spray with clopyralid or metsulfuron-methyl.

Photos

View plumeless 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
Links for more information.