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PlumelessThistle

Carduus acanthoides

What is it?

Plumeless thistle (Carduus acanthoides) is a winter annual or biennial that is native to Europe and Asia. Plumeless thistle rosettes have wavy leaves with yellow spines along the white-colored leaf margins. The stems are covered with leaf-like, winged spines that extend up to the flowering heads. The flower heads, in clusters of 2 to 5, are alone at the end of the branches. They are purple to dark red in color and are 1/2 to 1 inch in diameter. Leaves are alternate, stalk-less, hairy underneath and blend into the stem. Mature plants can grow taller than 5 feet and can produce upwards of 9,000 seeds (CSU, 08/08).

 

Why is it a problem?

Plumeless thistle can be invasive: in pastures, fields, disturbed lands, logged-over areas, river valleys, along roadsides and in native grasslands. Plumeless thistle out competes native species and forage crops. It is one of the most aggressive thistles, due to its high seed production. Plumeless thistle is unpalatable to livestock and it may accumulate nitrates (CSU, 08/08).

This perennial is also invasive throughout New Mexico.

 

Management Techniques:

The key to effective control of Plumeless thistle is very similar to Musk thistle. Preventing Plumeless thistle seed production and planting desirable grasses and forbs to out compete Plumeless thistle is effective. Plants over winter and grow from seeds and rosettes. The seed viability for Plumeless thistle is unknown. The site must be monitored for at least 10 years after the last flowering adult plants have been eliminated and treatments repeated when necessary (CSU, 08/08).

  • Plumeless thistle is designated as a “List B” species in the Colorado Noxious Weed Act. It is required to be eradicated, contained, or suppressed depending on the local infestations. For more information visit www.colorado.gov/ag/csd and click on the Noxious Weed Management Program. Or call the State Weed Coordinator at the Colorado Department of Agriculture, Conservation Services Division, at (303)-239-4100

 

  • Biological control insects, such as the seed head weevil and the crown weevil are effective on large infestations. When used together, these insects provide fair to good control. These insects have been known to threaten native thistle populations (CSU, 08/08).

  • Contact the Insectary of Colorado Department of Agriculture to get complete information at 970-464-7916 or visit www.colorado.gov/ag/csd.

  • Any mechanical or physical method that severs the root below the soil surface will kill Plumeless thistle. Mowing or chopping is most effective when Plumeless thistle plants are at full bloom. Be sure to properly dispose of the flowering cut plants since seeds can mature and become viable after the plant has been cut down (CSU, 08/08).

  • Note: Contact your local county agent for herbicides applications

 

What we can do:

  • An integrated weed management approach is an effective tool when dealing with Plumeless thistle; using herbicide, biological and cultural control methods.

 

General Information on Plumeless Thistle:

Natural Resource Conservation Service

  • Website that provides information, locations, classification, legal status, and related links

 

Colorado State University Extension

  • Website that provides identification, biology, & control of Plumeless Thistle

 

Colorado Weed Management Association

  • Website that provides information, habitat, identification, impacts, biology and control of Plumeless Thistle

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