Invasive Plants in Pennsylvania Musk Thistle Carduus nutans L. Description

 

Invasive Plants in Pennsylvania 

 

Musk Thistle 

 

Carduus nutans L. 

Description: 

 

Musk thistle is an herbaceous, 

biennial plant that grows one 

to six feet tall.  It has showy, 

red-purple flowers that appear 

from June to September.  

Flowers are one to three inches 

in length and tend to droop 

once mature.  Leaves and 

multi-branching stems are 

very spiny.  Leaves are dark 

green, coarsely lobed and have 

a smooth, waxy surface.  

 

 

Range: 

 

Musk thistle is found  

throughout the continental 

U.S. except for some New 

England states and Florida. 

Background: 

 

Also known as nodding               

thistle, this plant is native to                  

western Europe and Asia.  It 

was accidentally introduced 

into the United States in the 

early 1900s.  It was first                  

discovered in Tennessee in 

1942 and has been declared a 

noxious weed in many states. 

 

Habitat: 

 

Musk thistle will invade a             

variety of disturbed areas and 

grow in neutral to acidic soils.  

Pastures and meadows are at 

particular risk because live-

stock will not eat it.  It does 

not grow well in excessively 

wet, dry or shady conditions. 

Biology and Spread: 

 

Each plant may produce up to 

120,000 straw-colored seeds 

each year.  These seeds may 

remain viable in the soil for 

over ten years, making control 

difficult.  Seedlings emerge in 

mid to late July and develop 

into a rosette of leaves.  The 

second year, the multi-

branching stems emerge and 

flowers bloom.   

 

Ecological Threat: 

 

Once this plant is established 

it can spread rapidly due to 

high seed production and lack 

of animals that will feed on it. 

 

 

Photo: Ricky Layson, 

www.invasive.org

 

Photo: Loke Tok, Virginia Polytech, 

www.invasive.org

 

Photo: Norman Rees, USDA, 

www.invasive.org

 

Manual and Mechanical 

 

Hand pulling is most                   

effective on small populations 

and can be done throughout 

the year, but is most effective 

prior to flowering.  Flowers 

and seeds should be bagged 

and disposed of in a landfill 

to minimize seed dispersal.  

Minimizing soil disturbance 

will help limit the chance of 

plant germination from the 

seed bank. 

 

 

Look-A-Likes: 

 

Native species of thistle 

(Cirsium sp.), some of which 

are rare, could be confused 

with musk thistle. Before               

control is attempted, the               

thistle species in question 

should be accurately                      

identified. 

References: 

 

Plant Conservation Alliance’s Least Wanted List:  

http://www.nps.gov/plants/alien/fact/canu1.htm

 

 

Invasive Species and Ecosystem Health Network:  

http://www.invasive.org

  

 

 

 

 

For More Information: 

 

Plant Invaders of Mid-Atlantic Natural Areas, National Park Service: 

http://www.nps.gov/plants/alien/pubs/midatlantic/

midatlantic.pdf

  

 

Invasive Plants Field and Reference Guide, U.S. Forest Service: 

http://na.fs.fed.us/pubs/misc/ip/ip_field_guide.pdf

  

 

DCNR Invasive Species Site: 

http://www.dcnr.state.pa.us/

conservationscience/invasivespecies/index.htm

 

Chemical 

 

Foliar application of a                    

systemic herbicide like                   

glyphosate or tricloyr is                   

effective at controlling musk 

thistle.  Apply a two percent 

solution of herbicide mixed 

with water and a 0.5 percent 

non-ionic surfactant to the 

leaves.  Treatment should be 

done during the rosette stage 

or prior to flowering.  Be sure 

to follow all label instructions 

and state herbicide                         

regulations. 

Native Alternatives 

 

Musk thistle is not a popular 

ornamental and is not usually 

planted intentionally in the 

landscape.  However, after its 

removal you can replace it 

with a variety of attractive            

native plants like butterfly 

weed (Asclepias tuberosa), Joe-

pye weed (Eupatorium 

dubium), ironweed (Vernonia                  

noveboracensis) and black-eyed 

Susan (Rudbeckia fulgida).   

How to Control this Species: 

Photo: Jessica Sprajcar, DCNR 

Ironweed 

Chris Evans, River to River CWMA 

www.forestryimages.org

 

Field Thistle