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Plumeless thistle (Carduus acanthoides)
Large herbaceous biennial. When the plant bolts in the second year it can be 3-6’ tall. Stems are freely branching and have leaf like spines.
Overview
Plumeless thistle is Restricted (Orange counties)
Other names for this plant include:
- Common names: spiny plumeless thistle, welted thistle
Ecological threat:
- Infest low quality areas first such as roadsides, disturbed areas, ditch banks, and old fields and 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.
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 developed by the department.
Identification
First year plants-Leaves: First year rosette leaves are up to 2’ long, deeply divided with lobes ending with spines.
Second year plants-Leaves: Dark green with light green midrib and hairy on underside; leaves are deeply divided with lobes ending in a spine.
Flowers: Red-purple flowers singly or in clusters. Flower heads are up to 1” in diameter.
Fruits & seeds: Up to 10,000 seeds per plant with seeds disperse within 7-10 days of flowering. Seeds are viable in soil for more than 10 years.
Roots: Single taproot.
Similar species: Musk thistle (Carduus nutans) is very similar except for the flower is much larger, 1.5-3” wide, solitary, and slightly nodding. The leaves are also hairless on both sides.
Distribution
Counties in WI where plumeless thistle has been reported (as of July 2011). Both vouchered and unvouchered reports included.
Do you have plumeless thistle in your county but it isn't shaded on the map? Send us a report.
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 sharp shovel 1-2” 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
