Italian thistle

Carduus pycnocephalus

   

Family: Asteraceae

Other common names: Plymouth thistle, shore thistle

Weed Class: A

Year Listed: 1991

Native to: Northern Africa, Asia and Western and Southern Europe

Toxic: not known to be

Other Legal Listings: WA Quarantine list, WAC 16-750

additional photos

 

   

Why is it a noxious weed?

Italian thistle invades pastures and rangeland. It crowds out more desirable forage, as well as native plants, and excludes livestock grazing where infestations are dense.

How would I identify it?

General Description: Italian thistle is a spiny annual or sometimes biennial that can grow 6 to 8 feet in height.

Flower Description: Flowerheads narrow and in terminal clusters of 1 to 5. Bracts at the base of flowerheads are stiff and upright with forward pointing hairs. Flowers are purple.

Leaf Description: Leaves green and nearly hairless above and have cobwebby hairs below. Leaves are pinnately lobed into spiny-lobed segments, with the terminal spine being most prominent.

Stem Description: Italian thistle has spiny, winged stems.

Fruit/Seed Description: Seeds are light brown to brown with veins, 0.18 to 0.24 inches (4 to 6 mm long), with hairs attache at one end.

May be confused with: Slenderflower thistle, Carduus tenuiflorus, is similar but it generally has more flowerheads (5-20), than Italian thistle, Carduus pycnocephalus (1-5 flowerheads).

How does it reproduce?

Italian thistle reproduces by seed.
 

Where does it grow?

It grows in dry, open area such as pastures, rangeland, right-of-ways, and waste areas. Please click here to see a county level distribution map of Italian thistle in Washington.
 

How do I control it?

Cultural Control

Deferring autumn grazing of sheep has been effective in reducing stand density because the thistles grow etiolated and less spiny when competing with ungrazed grasses. Then sheep will graze the thistle along with the grass.

Biological Control

Two fungi have been evaluated as agents on Italian thistle. More information can be found by downloading our Written Findings.

Herbicide Control

Please refer to the PNW Weed Management Handbook, or contact your county noxious weed coordinator.


 

For more information

 
See our Written Findings for more information about Italian thistle (Carduus pycnocephalus).
See our postcard for early detection information about Italian and slenderflower thistle.

Additional Photos


 
 

 


Italian thistle

 


Italian thistle growth

 


Blooming flowerheads

 


Plant habit

 


Leaves

    

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