Diffuse Knapweed

Diffuse Knapweed Diffuse Knapweed BudDiffuse KnapweedDiffuse Knapweed Root


Centaurea diffusa Lam.
Asteraceae (Sunflower family)

Colorado Dept. of Agriculture Class B Stop the spread
Jefferson County, CO

List B Eradication Required

Aliases: Spreading knapweed, tumble knapweed, white knapweed
Annual: (1yr life cycle). Most commonly a short-lived perennial (survives the winter but doesn’t do well the 2nd yr.); occasionally a biennial (needs 2yrs to complete its life cycle).

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Weed War

Weeds are a growing concern in our neighborhood. Many homeowner associations and individuals informed C.A.R.E. that they felt overwhelmed by the numbers of weeds after last summer’s rains, particularly, the Bull, Canada and Musk thistles.

Even thickets of thistles like this can be overcome; read about how to achieve a thistle-free pasture that looks like this:


The Mission of the C.A.R.E. Weed Committee is to maintain the natural heritage of the neighborhood we live in by preserving native plant species as well as mitigating against the spread of invasive weed species. By working with nature we can preserve the essence of the Ponderosa Pine Woodlands and Savanna natural communities that are located within our neighborhoods. Together we can reduce the use of water, reduce erosion, reduce the risk of fire (native species are tougher during droughts) and enhance the natural beauty of this unique part of Colorado, making our neighborhoods more beautiful, sustainable and safer.

Neighbors who had worked hard to eliminate noxious weeds despaired because neighboring areas were infested, so the weeds would return. C.A.R.E. hopes to help share information on what works, investigate grants and foster cooperation in dealing with this invasion. C.A.R.E. is contacting Jefferson County regarding the weeds on Apex Trail and along Denver rights-of-way over weeds on their lands that lie in our neighborhoods. Mount Vernon Country Club Metro District pioneered the use of goats several years ago because weed seeds swallowed by goats are destroyed in their digestive systems. Mount Vernon is now experimenting with the use of a fungus that only attacks thistle. Genesee has shown good weed control over the years.

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Thistle Before and After/ Fall & Late Summer Information


1988 July Canada Thistle and deer from Yvonne Micke



1988 Comparison then & now Elk and deer at Rilliet ParkPost Canada Thistle treatment


Canada Thistle (Late Summer)

You might as well mow the area now (saving the step of cutting the seed heads only).

We can’t stress enough that if you will use a bag on your mower to collect all cuttings, you will greatly reduce the number of seeds left on the ground to germinate next year. If you do not use a bag when cutting, we recommend that you rake the area and bag as many white fluffy seed heads as possible for containment.
Now spray the weed infested area. The before and after pasture picture recently posted, and again here, is a result of a Commercial Spray Company spraying for 3 consecutive years.
As any new Canada rosettes appeared in the interim (and they will) Yvonne spot sprayed the weed using a selective weed killer which she purchases from Abners on 44th or Echter’s on 52nd & Garrison (or other smaller garden centers) to insure that she is getting the spray with a 47% formula/active ingredient VERSUS purchasing from the larger box stores where the concentration is milder at 4%. The best reason she uses this concentrate, is that it does not kill her grasses. She follows the directions specifically. and never tries to  mix a stronger solution, as this is a case where “more is not better”.

Musk Thistle (Late Summer)
This late in the season, DO NOT MOW your blooming Musk Thistle! You will just be spreading the seed to form new plants next year. Place a bag over the seed head while you’re digging it up to help prevent the jostling of the seeds. We can’t stress enough, that if you will dig up your Musk Thistle, you will KILL THE PLANT FOREVER. Yes, you will have new rosettes next year from the seed on the ground this and previous years, but you won’t continue to have the same plants.
If you have already cut the seed heads off your Musk Thistle (your neighbors and we thank you) they have most likely been trying to regenerate a new bud (much smaller purple and not necessarily at the top of the plant). Dig the plant up and it’s over. At a minimum, cut the new seed head, bag it and then spray the rosettes next Spring.

If you have mowed your area some time ago, you’ve probably discovered the Musk Thistle has resurged and formed again with numerous patches of rosettes. Remove any buds that have formed and dig them up or spray them now. If you don’t kill the plants/rosettes now, you will continue to deal with more Musk Thistle next year.

The key to weed control is the prevention of seeds. Next spring, before either the Canada or the Musk form a flower bud, spray the Canada, and dig the Musk. If you are going to hire a commercial spray company, start early, they get busy (see our list of recommended spray companies on the CAREjeffco.org web site). Most suggest you spray early spring when the weeds are a few INCHES high. You’ll then be on your way to a Thistle free acreage.



Dalmatian Toadflax

Version 2

Dalmatian Toadflax flower
Dalmatian Toadflax flower
Toadflax root system
Dalmatian Toadflax Root

Linaria dalmatica ssp. dalmatica
Figwort Family

Colorado Dept. of Agriculture Class B

Aliases: Balkan toadflax, broadleaf toadflax, wild snapdragon, smooth toadflax
Perennial: Forb
Flowers/Fruit: Seeds Mature July – September. (Oct. after the 1st year)
Flowers: Snapdragon type, bright yellow, tinged with orange,  1-1/2 “ long spur. The upper lip is 2 lobed and the lower is 3 lobed.
Bloom: May – August
Upright, branching toward the top up to 3-4 ft. tall. A single Toadflax plant contains from 1 to 25 vertical, Floral stems which are thick walled and somewhat woody. Prostrate stems are tolerant to freezing.
Leaves: Light to bluish-green waxy leaves are broad, alternate, ovate, sometimes heart-shaped and upper leaves clasp the stem (an important difference to Yellow Toadflax). Leaves get progressively smaller up the stem.
Root: Roots may grow 20 inches deep or more and lateral roots may extend 10 ft. from the parent plant. Very aggressive.
Reproduce: By seed (500,000seeds or more/plant) as well as by horizontal or creeping rootsystem. Seeds are irregular in shape, tan-gray and 1/24” to 1/16” across.
Seed Viable: 10 Years
Mechanical Control: The combination of spraying and seeding competitive grasses control Dalmatian Toadflax better than spraying alone. Hand Pulling or digging up the roots for an average of 6 years. Plants will re-sprout from root fragments. Spray at flowering or in the fall.
Interesting Facts: It was introduced into the Western US in 1874. Broad leaved Dalmatian Toadflax (L. dalmatica) has been cultivated as an ornamental plant for at least 400 years. Used for centuries as a folk remedy and a dye. Extensive root system outcompetes other plants for nutrients and water. Contains toxic chemicals that can cause liver damage in grazing animals.
Dalmatian Toadflax differs from Yellow Toadflax principally in being larger and having different shaped leaves.
In Colorado, Dalmatian Toadflax shoot density increased over 1,200 percent in six years at one location, and 190 percent over 3 years at another.

Jefferson County Information Sheet Link

Colorado Department of Agriculture fact and treatment Link

Canada and Musk Thistle

Cirsium arvense

Canada Thistle Rosette


Carduus nutans


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.


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.



Common Mullein


Verbascum thapsus L. (Scrophulariaceae)
Colorado Dept. of Agriculture C List for Containment
ig the rosettes or spray. Cut off flowering heads and Bag.

Early Stage Common Mullein

Apex Trail 2015
Trail 2015

Common Mullein dried
P1020541 Common Mullein Root Common Mullein Common Mullein


Aliases: Aaron’s rod, Adam’s flannel, beggar’s blanket, beggar’s flannel, beggar’s stalk, big taper, blanket herb, blanket leaf, bullock’s lungwort, candlewick plant, clot, clown’s lungwort, cow’s lungwort, cuddy’s lungs, devil’s-tobacco, duffle, feltwort, flannel leaf, flannel plant, fluffweed, golden rod, great mullein, hag’s taper, hare’s beard, hedge-taper, ice leaf, Jacob’s staff, Jupiter’s staff, lungwort, miner’s candle, mullein, mullein dock, old man’s flannel, Our Lady’s flannel, Quaker rouge, rag paper, shepherd’s club, shepherd’s staff, St. Peter’s staff, torches, torchwort, velvet dock, velvet plant, white man’s-footsteps, wild ice leaf, witch’s taper, woolen, wooly mullein.

Biennial: Forb
Flowers/Fruit Has a flowering stalk (up to 20”). The 2 celled fruit contains many grooved seeds.
Flowers: Are sulfur yellow with five petals, about 3/4″ to 1-1/2″ diameter.
Bloom: June to August/September. Bloom a few at a time on the same stalk. Yellow flowers turn brown as seeds mature.
Stem: Unbranched can be up to 6 ‘ to 8’ tall.
Leaves: 1st year form basal rosette (up to 30” in diameter) and develop seedling leaves.
2nd yr. Leaves become large, (up to 1 ft. long), overlapping, oblong, hairy, alternate and whitish green which progressively get smaller up the stem.
Root: Shallow taproot along with a fibrous root system.
Reproduce: By Seed Only (100,000 to 250,000 seeds /plant). Takes 2 weeks to germinate.
Please do not cultivate this plant. Remove any dried stalks to reduce fire danger.
Seed Viable: Up to 100 yrs.
Mechanical Control: Cutting and Bagging (carefully) the flower stalk before going to seed. Hand Pull or dig entire plant (best when soil is moist) before flowers appear.
Sowing bare ground with early native grasses or other plants may decrease seed germination.
Herbicides must be applied before late flowering stage or seeds may still be produced. Rosette stage works best.
Interesting Facts: The plants were originally from Europe/Asia. The Europeans used the flowers for tea, and the leaves for many remedies like burns and rashes. Both the Europeans and the Indians smoked the dried leaves to treat bronchitis. Used as a fish poison. A methanol extract has been used as an insecticide for mosquito larvae. Mullein stalks were traditionally used as a cheap torch.  Mullein is Latin for “soft”.  Was used for lamp wicks before cheap cotton was available.  Mullein oil used to naturally treat dog ear infections.  Quaker women rubbed Mullein leaves on their cheeks to make them pink.  Anyone using Mullein leaves as toilet paper found their cheeks pink as well.
For further assistance or information:

Common Mullein Factsheet
Jeffco Common Mullein Information


Purge Your Spurge, Myrtle Spurge

Purge Your Spurge! Event Aims to Help Eradicate Toxic Weed

You may have seen it in a neighbor’s yard. Maybe you have it in your own yard. And maybe you even think it is somewhat attractive. But the truth is, there is nothing pretty about the noxious weed Myrtle spurge. Jefferson County Weed & Pest needs your help in getting rid of this plant that takes over the landscape and is a danger to people, desirable plants and wildlife.

Myrtle spurge (Euphorbia myrsinites) is a highly invasive ‘List A’ noxious weed that is required by the Colorado Noxious Weed Act (C.R.S. 35-5.5-101-119) to be eradicated. Myrtle spurge contains a toxic, milky sap which can cause severe skin irritations, including blistering. Hand-pulling, digging, and herbicide applications are effective methods used to control it. It is highly recommended to wear gloves, long sleeves, shoes and eye protection when in contact with Myrtle spurge as all the plant parts are considered poisonous.

Identifying Myrtle Spurge: This weed, also called donkeytail spurge or creeping spurge, is a low-growing perennial with trailing fleshy stems which spreads rapidly to surrounding areas and can ‘jump’ fences to natural areas and displace native vegetation and reduce forage for wildlife. The leaves are fleshy, blue-green and alternate; the flowers are bright yellow-green, petal-like, and appear from February to May.

Jefferson County Weed & Pest is partnering with Wildland Restoration Volunteers (WRV) to raise awareness and ensure eradication of Myrtle spurge.  For more information about WRV and other Purge Your Spurge visit their website at www.wlrv.org.

Alicia Doran, County Weed & Pest Management Specialist
303-271-5989, adoran@jeffco.us

Katie Matthews

Community Relations and Marketing Coordinator

Jefferson County Open Space

303-271-5960 Direct  720-415-9173 Cell