Musk thistle (Carduus nutans)

Berries and leaves of Amur cork tree

 
 

Musk thistle is a biennial thistle that is a rosette of leaves in its first year and sends up a flowering stalk in its second year, then dies. Musk thistle is also sometimes called "nodding thistle" because the flower heads can droop to a 90 degree angle instead of facing toward the sky. Musk thistle is primarily an issue in overgrazed pastures and disturbed areas and is generally not a threat to intact prairies.

Caution: Plants have spines along leaves and stems.

Description

Appearance

Musk thistle is a biennial herbaceous plant. In its first year, it grows as a group of leaves (rosette) near the ground. Plants overwinter in the rosette stage, then the next spring the plants send up a flowering stalk, set seed, and die. Flowering stalks can grow up to seven feet tall.

Leaves and Stem

In the first year, the plant is a rosette of leaves near the ground. Rosette leaves can be ten or more inches long, have deep lobes, and edges with spines. In the second year, the plant puts up a flowering stalk that can have branching stems. Leaves are alternate (come off the stem one at time at each leaf node). Leaves are spiny, lobed, dark green with light green midrib, smooth, and hairless. Stems have sharp spines.

Flowers

Disk-shaped flower heads contain hundreds of tiny individual purple flowers that bloom from June through July. Flower heads can be 1.5 - 3 inches wide. Bracts (small pointy leafs) below the flower head have sharp points. Flower heads droop to a 90 degree angle from the stem when mature.

Seeds

The small seeds have feathery, white tufts to help with wind dispersal although most seeds land within 160 feet of the parent plant.

Roots

Each plant has a fibrous taproot.

Biology

Musk thistle is a biennial herbaceous plant. In its first year it grows as a rosette of leaves near the ground. Plants overwinter in the rosette stage, then the next spring the plants send up a flowering stalk, set seed, then die. Musk thistle grows best in disturbed areas such as pastures, roadsides, and ditch banks, but also in hayfields and disturbed prairies.

Origin and Spread

Musk thistle is native to Europe. It was accidently introduced to the United States in the early 1800s likely as a contaminant in seed mixtures and ship ballast. Musk thistle is widespread in the United States and Minnesota.

Refer to EDDMapS Distribution Maps for current distribution.

Don't be fooled by these look-alikes

  • Plumeless thistle, Carduus acanthoides (invasive) - is very similar to musk thistle especially in the rosette stage. Plumeless thistle flowers are one-third the size of musk thistle and do not nod. Plumeless thistle has hairs on the underside of its leaves while musk thistle leaves are hairless.
  • Canada thistle, Cirsium arvense (invasive) – Canada thistle has small flowers (3/4 inches long) and its stems generally do not have spines on them.
  • Bull thistle, Cirsium vulgare (invasive) – bull thistle stems can have green vertical ridges with spines, leaves have hairs, and the topside of the leaf is rough.
  • Swamp thistle, Cirsium muticum (native) – swamp thistle does not have the sharp bracts underneath the flower head that musk thistle has. Minnesota has several native thistle species.

View the Minnesota thistle comparison by the Friends of the Eloise Butler Wildflower Garden for descriptions and photographs of the species.

 
Regulatory Classification

Musk thistle is not regulated on a statewide level although some counties list it as a county noxious weed.

Threat to Minnesota
  • Musk thistle generally does not pose a threat to high quality areas. It colonizes primarily disturbed areas such as pastures, roadsides, and ditch banks.
  • Musk thistle is distasteful to grazing animals, giving the thistle a competitive edge. Pasture management techniques can reduce musk thistle in pastures.
What you should do

One way that invasive plant seeds and fragments can spread is in soil. Sometimes plants are planted purposefully. You can prevent the spread of invasive plants.

PlayCleanGo: Stop Invasive Species in Your Tracks

  • REMOVE plants, animals & mud from boots, gear, pets & vehicle.
  • CLEAN your gear before entering & leaving the recreation site.
  • STAY on designated roads & trails.
  • PLANT non-invasive species.
Native Substitutes
 
Control Methods

Mechanical control can be done by pulling the plant by hand or with equipment such as a shovel. If pulling plants, leave plants to decompose on-site or follow Minnesota Department of Agriculture guidance for plant disposal. Mow second year stalks in May or June during the flower bud stage. Do not mow after plants have gone to seed as this will spread seeds. Contact University of Minnesota Extension for advice related to pasture management.

Herbicide control can be done using systemic herbicides which are taken up by plants and move within the plant, which can kill leaves, stems, and roots. Spot-spray with glyphosate, triclopyr or 2,4-D. The most effective timing is to apply herbicide to the rosettes in spring (April, May or June) or fall (October or November).

Reporting

If you live in a county where musk thistle is regulated as a county noxious weed, report new occurrences by contacting your local county agricultural inspector. For most of Minnesota, this species is unregulated, but you can add to the public information about this species by reporting new occurrences through EDDMapS Midwest.

Resources