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Class A Noxious Weed

Italian Thistle
Carduus pycnocephalus
 

Italian Thistle flower


Plant family: Compositae
Year listed:
Native to: Western and southern Europe.

Why is it a noxious weed?
Italian thistle invades range and pastures. On grazed lands, like other thistles can reduce productivity by physically interfering with grazing and by displacing desired grasses. Native vegetation is threatened by this aggressive weed that tends to form dense stands.

How would I identify it?
General Description: Broadleaf weed that can grow 6 to 8 feet in height.

Leaves:

  • oblanceolate to lanceolate to 15 cm long and 8 cm wide
  • pinnately divided into spiny-toothed or lobed segments
  • terminal spine of the segments and lobes the most prominent and rigid
  • underside of stems are covered with cobwebby hairs

Flowers:

  • 1 - 5 pinkish, cylindrical flower heads are born in terminal clusters 

Stems:

  • spiny-winged stems
  • underside of stems are covered with cobwebby hairs

Line drawings are taken from 1,000 Weeds of North America, copyright of XID Service, Inc and used with permission. Permission granted by the author.

How does it reproduce?
Italian thistle reproduces by seed.

Where does it grow?
Dry, open area such as pastures, range, and right-of-ways, also waste areas.

What is the distribution in Washington State?
 

 

  • Distribution map not available at this time.

How do I control it?

Cultural: 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.

Herbicide: The rates for various chemical control options are found in the annually updated Pacific Northwest Weed Control Handbook, or contact your county weed coordinator.

Mechanical: Tilling or digging will kill Italian thistle.

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

Are there plants that may be confused with Italian thistle?

Slenderflower thistle (C. tenuiflorus), a Class A noxious weed in Washington State. If you need help with identification, contact your county weed coordinator.

For more information
For more information, download our Written Findings.

 

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Italian Thistle infestation
Italian thistle infestation photo.

 Last updated September 10, 2008