Canada and Musk Thistle

CANADA THISTLE
Cirsium arvense

Canada Thistle Rosette

P1020355

MUSK THISTLE
Carduus nutans

 P1020131

Musk Thistle (Early)

Musk Thistle Mature
Musk Thistle Mature

Perennial:  Forb
Flowers/fruit: Small bristly clusters 1 to 5/branch. Size: ½ to ¾ in. wide. May produce 1,000 to 1,500 seeds/flowering shoot. Bracts are spineless.
Bloom: June–Aug./Sept.
Stem: Height to 4-6’ hollow, smooth around the top to hairy below, branching at the top.
Leaves: Variable
Root: Can spread 18 ft. wide and 15 ft. deep.
Reproduce: By Seed & Rhizome
Seed Viable:  20 yrs
Mechanical Control: Continually stress plant by cutting at ground level every 10-21 days. DO NOT PULL! After blooms form, cut the heads and bag.
Chemical Control: Please go to the links at the bottom of this article for recommendations from Colorado Dept. of Agriculture (pg. 2) and from Jeffco (follow their Link).
Interesting Fact: A segment as small as 0.25 by 0.125inches can store enough energy to produce a new plant.
Note: According to US Dept. of Interior Land Management WY it disperses a chemical that may inhibit growth of other plants.

https://www.colorado.gov/pacific/sites/default/files/CanadaThistleFactsheet.pdf
http://jeffco.us/weed-and-pest/weeds/weed-identification/canada-thistle/

Biennial, or sometimes winter annual: Forb,
Flower/fruit: Solitary, terminal, showy. Size is 1½ – 3 in. wide, flat, nodding. Color: deep rose, violet or purple, rarely white, surrounded by many lance-shaped, spine-tipped bracts.
Bloom: May-July or June-Oct.
Stem: Hairless, can grow  up to 8 ‘
Leaves: Lobed, wavy white outlined margins, dark green, light green midrib, hairless on both sides, long sharp spines.
Root: Taproot can extend to 2 ft. deep
Reproduce: By seed (1,200/flower). Approx. 1/3 viable .
Seed Viable:  10 yrs.
Mechanical Control: By pulling or digging the Musk Thistle before going to seed you will eradicate the plant for good. The root system does not extend beyond the individual plant.  However new plants may still evolve from viable seeds from previous years.
Chemical Control: Please go to the links at the bottom of this article for recommendations from Colorado Dept. of Agriculture (pg. 2) and from Jeffco (follow their Link).
Interesting Facts: The bract under the flower is a very distinctive identification feature. Colorado is home to 20 native thistles of which 8 are noxious.
https://www.colorado.gov/pacific/sites/default/files/Musk%20thistle%20Fact%20Sheet_1.pdf
http://jeffco.us/weed-and-pest/weeds/weed-identification/musk-thistle/