plumeless thistle
(Carduus acanthoides)

plumeless thistlePhoto By: Washington State Noxious Weed Control Board

Roots: The roots of the plumeless thistle are large wide spreading taproots. (2)

Stems/ Leaves: The stem of the plumeless thistle is stiff, and it may grow to more than 5 feet high.  The stems are usually only about 1 to 4 feet tall.  The stem containes many branches off of it all the way up the top. (1)  The leaves are similar to that of the musk thistle, but the plumeless thistle leaves don't have the white border around them.  The leaves are also a lot skinnier than those on a musk thistle.  The leaves also usually are about 6 inches long. (2)

Flowers: The flowers of the plumeless thistle are very small (usually between 1/2 inch and 1 inch in diameter).  The flowers are numerous and are a bright pink or purple in color.  The flowers may be by themselves or in clumps.  These plants usually flower between May and August. (2)

Fruits and Seeds: Plumeless thistle do not bear fruit.  The seeds are relatively small, and usually grey or tannish in color.  The look a lot like a sunflower seed without the shell on it. (1)

Reproduction: Plumeless thistle reproduces when the seeds off of the flowers.  They are usually spread by the wind and by animals. (2)

Lifestyle/Habits/Life Duration: Plumeless thistle is a winter annual or biennial. (2)

Environments Favorable to Infestation: The areas that plumeless thistle is most often found in are in dry pastures, along roadsides, and also in creek bottoms. (3)

Methods of Control:
Biological Control: The three main insects are used to kill plumeless thistle are the seed-head weevil (Larinus planus), rosette bud weevil (Trichosirocalus harridus), and the seed-head gall fly (Urophora quadrifasciata).  They are all effective at different stages.  For example the seed-head weevil is only useful when the plumeless thistle flowers for the first time. (4)

Cultural Control: Having healthy plants that are wanted in that area (a healthy plant community) do help choke out plumeless thistle. (3)

Mechanical Control: Digging, pulling, and mowing plumeless thistle is somewhat effective as long as these methods are done before the plant flowers and goes to seed.  These methods are effective because the seeds are the only way plumeless thistle can be spread. (3)

Plumeless Thistle Links

1) Plumeless Thistle. 10 February 2006, <>.

2) Plumeless thistle. 11 February 2006, <>.

3) "Carduus acanthoides." Plumeless Thistle. 11 February 2006, <>.

4) Nodding and Plumeless Thistle. 13 February 2006, <>.

Created By: Keith Dosland, 2/21/06.      Back to NEW WEED ALERTS HOME