Weed of the Month
Learn about noxious weeds and steps you can take to manage or eradicate. Each month we will bring you a new profile and helpful resources.
June Weed Profile
Plumeless Thistle
Carduus Acanthoides
Plumeless thistle (Carduus acanthoides) is a List B member of the Sunflower family (Asteraceae). It is a biennial or sometimes a short-lived perennial.
Flowers are reddish-purple, ½-1 inch wide. The bracts are narrow and tipped with a spine. Flowers are present June to September and grow singly or in small groups at the tips of branched stems.
Plumeless thistle reproduces by seed. The seeds lack a pappus.
Plants have taproots and can grow to 8 feet tall. Stems are winged and branch towards the ends. Leaves are dark green with a lighter midrib. The undersides of the leaves are hairy.
Rosettes form in the first year and bolt early in May to June of the next year. The rosette leaves are deeply lobed and spiney.
Plumeless thistle is found in disturbed areas, such as overgrazed pastures, rangelands, roadsides, and rights-of-way.
Originally from Eurasia, it has been known in the northeast US since 1837 and in Colorado since the mid-1950s.
RESOURCES
MN Dept. of Agriculture
https://www.mda.state.mn.us/plants/pestmanagement/weedcontrol/noxiouslist/plumelessthistle
WASHINGTON STATE Noxious Weed Control Board
https://www.nwcb.wa.gov/weeds/plumeless-thistle
PHOTO CREDITS
Rosette – Loke T. Kok, Virginia Polytechnic Institute and State University, Bugwood.org
Stem – Steven Katovich, Bugwood.org
All others: Jeffco Invasive Species Management
Items of Interest
Weed of the Month
2023
January Weed Profile – Common Mullein
February Weed Profile – Cypress Spurge
March Weed Profile – Dames Rocket
April Weed Profile – Sulfur Cinquefoil
May Weed Profile – Poison Hemlock
June Weed Profile – Plumeless Thistle
2022
January Weed Profile – Knotweed
February Weed Profile – Rush Skeletonweed
March Weed Profile – Black Henbane
April Weed Profile – Chinese clematis
May Weed Profile – Houndstongue
June Weed Profile – Milk Thistle
July Weed Profile – Oxeye Daisy
August Weed Profile – Spotted Knapweed
September Weed Profile – Perennial Pepperweed
October Weed Profile – Yellow Flag Iris
November Weed Profile – Common St. Johns Wart
December Weed Profile – Field Bindweed
2021
January Weed Profile – Dalmatian Toadflax
February Weed Profile – Common Mulllein
March Weed Profile – Mediterranean Sage
April Weed Profile – Saltcedar
May Weed Profile – Absinth Wormwood
June Weed Profile – Eurasian watermilfoil
July Weed Profile – Yellow starthistle
August Weed Profile – Hairy willowherb
September Weed Profile – Yellow toadflax
October Weed Profile – Chamomile
November Weed Profile – Diffuse knapweed
December Weed Profile – Poison hemlock
2020
January Weed Profile – Cheatgrass
February Weed Profile – Myrtle Spurge
March Weed Profile – Hoary Cress
April Weed Profile – Leafy Spurge
May Weed Profile – Scotch Thistle
June Weed Profile – Dyer’s Woad
July Weed Profile – Orange Hawkweed
August Weed Profile – Purple Loosestrife
September Weed Profile – Teasel
October Weed Profile – Canada Thistle
November Weed Profile – Russian Knapweed
December Weed Profile – Russian Olive
