Figure Musk thistle flower. Figure Musk thistle rosette

Figure 2.  Musk thistle flower. 

 

 

Figure 1.  Musk thistle rosette. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Musk or nodding thistle (Carduus nutans) is 

a native of Europe and Western Asia.  It has been 

in the United States since the late 1800’s.  It was 

accidentally introduced and has spread rapidly in 

North America.  It is a prolific seed producer 

and, as an alien species, it lacks natural enemies.   

 

It is important to identify and eradicate musk 

thistle as soon as it is found.  It is a noxious 

weed in Nevada and many other states because it 

reduces forage yield and quality, makes 

recreation areas impassable, and degrades 

wildlife habitats.   

 

Identification 

 

Musk thistle is a biennial.  In its first year, it 

grows as a basal rosette (a plant with leaves 

radiating from the crown (center) close to the 

ground and without flower stalks) (Fig.1). The 

rosette may grow two feet in diameter.  Its waxy 

leaves appear pale blue-green because they are 

covered with whitish hairs. 

 

During its second growing season, musk 

thistle can grow to nine feet tall.  It has large, 

coarse stems that are covered with dense, short 

hairs.  The leaves are three to six inches long and 

alternate.  They are spiny, deeply lobed, long and 

narrow.  Musk thistle has a single, deep taproot 

that does not spread laterally.  The root is hollow 

at the top and has a corky texture throughout.   

 

During the second year, approximately 45 to 

55 days after bolting (producing a flower stalk), 

musk thistles produce seeds.  Fortunately, musk 

thistle only reproduces by seed; unfortunately, it 

is very prolific, producing a few thousand to 

100,000 seeds per plant.  On average, a plant 

produces 10,000 seeds.  Each seed has a bristle 

or pappus (stiff hairs) that aids in seed dispersal; 

however, animals, wind, birds, and water do not 

generally spread the seeds; but they may.  The 

majority falls close to the plant, resulting in 

thousands of new seedlings in the immediate 

area.  Musk thistle seeds may remain viable for 

more than 10 years in the soil. 

Musk thistle produces terminal flower heads 

from June through October (Fig.2).  It may also 

produce secondary heads that develop lower on 

the main branches.  All the flower heads 

(terminal and secondary) can emerge over nine 

Managing Musk Thistle 

 

Tina Kadrmas, Undergraduate Research Assistant, University of Nevada, Reno 

Wayne S Johnson; Associate Professor, Applied Economics and Statistics, College of Agriculture 

Biotechnology and Natural Resources; IPM Specialist, University of Nevada Cooperative Extension

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Bringing the University to You 

Fact Sheet-02-55 

Figure 3.  Musk thistle on rangeland.   

weeks.  In as little as seven days after the first 

bloom, and for a period of up to two months, 

seeds can be shed.  The flowers are one to three 

inches in diameter and deep rose to violet or 

purple colored; very rarely a white flower is 

produced.  Each flower has spine-tipped bracts 

(reduced leaf or leaf-like structure at the base of 

the flower) surrounding it.  The flower heads 

often droop or nod, giving the musk thistle its 

common name, nodding thistle (Fig. 3). 

Habitat 

 

Musk thistle is found in temperate climate 

zones and only occasionally in the tropics.  It can 

occupy saline soils in low valleys, as well as 

acidic soils at 10,000 feet.  Its seeds germinate in 

various ranges of environmental conditions.  It 

grows in 40 states, including arid Nevada and the 

moist climes of the East Coast.  Moisture and 

sunlight favor its establishment.  Pastures, 

construction sites, roadsides, ditches, gullies, and 

rangeland, particularly areas covered by 

snowdrifts, are ideal sites for musk thistle. 

 

Musk thistle does not become well 

established in vegetated sites where competition 

is great.  Healthy, dense pasture and rangeland 

vegetation prevents musk thistle from 

establishing.  However, competitive vegetation 

does not guarantee a musk thistle-free area, but it 

does reduce musk thistle establishment and 

dominance. 

 

Impact of Musk Thistle 

 

Coming in contact with musk thistle is very 

unpleasant.  A dense stand of musk thistle can 

act as a natural fence line or barrier on the range 

because of its spiny leaves.  Animals avoid musk 

thistle.  In pastures and rangeland, valuable 

forage is lost due to the presence of musk thistle.  

Livestock will not graze musk thistle nor near it.  

Sheep may graze it in its rosette stage, but only if 

there is nothing else to eat.  Similarly, musk 

thistle does not provide good forage for wildlife, 

thus reducing wildlife habitat value.  Wildlife 

may move to a new location if a significant 

portion of their habitat is infested with musk and 

other thistles.  A dense stand can make 

waterways inaccessible to wildlife, livestock, and 

recreationists. 

The quality of recreation is diminished when 

musk thistle invades trails and scenic areas.  

Trails become inaccessible, native vegetation is 

displaced (changing the natural landscape), and 

opportunities for wildlife viewing diminish as 

wildlife relocates. 

 

Management of Musk Thistle 

 

Because musk thistle is a biennial that 

reproduces only by seeds, it is more manageable 

than many invasive species.  Prevention is the 

key to controlling musk thistle.  Complete 

exclusion of the thistle is the most cost effective 

method of control.  If musk thistle does establish, 

prevention of seed production and dispersal is 

most important for a successful management 

program.  By combining several management 

techniques, musk thistle may be eradicated or 

controlled. 

 Prevention 

Prevention is the most time and cost effective 

of all the available techniques and must come 

first.   

Buy and plant certified weed-free seed to 

keep musk thistle out of new plantings.  When 

feeding livestock, make sure the feed, hay or 

grain, is certified weed free. 

Ensure equipment and vehicles are cleaned 

before leaving contaminated areas. 

On rangeland and in pastures, have a grazing 

management plan that allows desirable 

vegetation to recover from grazing.  To prevent 

musk thistle incursion, do not over graze a 

healthy pasture or rangeland.  A site with forage 

under stress and with open, disturbed patches 

allows musk thistle to establish. 

Monitor your property and adjacent lands for 

musk thistle and eradicate new plants whenever 

they appear.  Preventing seed production and 

dispersal is paramount.  Kill existing rosettes 

wherever they are found by tilling, cultivating or 

herbicide application.  Mow second year plants 

after the flower stalk is in the bud stage.  Earlier 

mowing may cause the plant architecture to 

change to a prostrate (laying flat on the ground) 

plant capable of producing flowers and seeds.  

Eradicating a small infestation of any weed is 

more cost effective and consumes less time than 

trying to control and eradicate a large stand. 

 Cultural Control 

Cultural control of musk thistle is limited.  

Good forage management practices that establish 

competitive desirable forage, maintain soil 

fertility, and prevent erosion will help combat 

musk thistle.  Perennial grasses are most 

competitive with broadleaf weeds in the western 

United States (Sheley and Petroff 1999).  

Research shows that musk thistle has declined 

over the years when perennial grasses are 

present. 

 Mechanical Control 

Mechanical control is effective on musk 

thistle.  Tilling, hoeing, and hand pulling must be 

completed either in the rosette stage or early 

after the flower stalk grows (bolts), but before 

the plant flowers and produces seed.  Hand 

pulling and hoeing are only an option for small 

stands.  To be effective, a successful revegetation 

program must follow tilling.  If this is not done, 

reinfestation of musk thistle is inevitable. 

Mowing is an option, but it can allow some 

musk thistle plants to recover and possibly sow 

seeds.  Mowing does reduce seed production, but 

should not be the single means of control in a 

management program.  It is most effective at the 

flower bud stage.  Mowing combined with an 

herbicide is more effective. 

Mechanical control is very effective in 

ditches, yards, construction sites and pastures.  

However, it may be difficult or uneconomical to 

use this method on rangelands. 

 Biological Control 

Grazing just to control musk thistle is not 

recommended.  However, using good grazing 

techniques will stimulate growth of native 

grasses and keep pastures healthy.  Since cattle 

will not graze musk thistle and sheep will only 

eat it in its rosette stage, it is difficult to maintain 

healthy pasturelands once they have been 

infested with musk thistle.   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

There are four insects in the United States 

that attack musk thistle.  Rhinocyllus conicus 

(Fig. 4) is a seed weevil that reduces seed 

production.  Trichosirocalus horridus, a beetle, 

eats the crown of the thistle, kills the apical (top 

or terminal bud of a stem) meristem (actively 

dividing tissues at the growing tips of shoots and 

roots), and reduces flowering.  The leaf feeding 

tortoise beetle, Cassida rubiginosa, feeds on the 

leaves, skeletonizing them.  This complements 

the damage of Rhinocyllus conicus and 

Trichosirocalus horridus.  Cheilosia corydon, a 

leaf and shoot miner, deposits its eggs in young 

leaves and shoots.  The larvae feed on the inner 

part of the leaves and shoots.  Hollowed out, 

they dry and break.  However, Rhinocyllus 

conicus is not host specific.  It has been released 

in Nevada near Verdi and is well established in 

the areas of Austin, Big Creek, and Grove’s 

Lake.  It will eat other thistles including native 

species, some of which may be endangered. 

 Chemical Control 

Numerous chemicals kill musk thistle.  

clopyralid, dicamba, MCPA, picloram, 

metsulfuron, chlorsulfuron, and 2,4-D have 

proven to be effective.  Which chemical to use 

and at what application rate depend on the 

 

Figure 4.  Rhinocyllus conicus adult laying eggs 

(left).  Rhinocyllus conicus larval-damaged 

seed (right). 

Photos courtesy of Oregon 

Department of Agriculture. 

location, environmental conditions, growth stage 

of the musk thistle, weather, associated species, 

soil-type, stand density, county or state 

regulations, and what is to be grown in the area 

in the future.   

In the rosette stage, clopyralid, dicamba, 

MCPA, picloram, and 2,4-D provide good 

control.  Application of these chemicals is 

usually suggested for the fall of the first year 

(rosette stage).  After the musk thistle bolts, 

metsulfuron and chlorsulfuron are effective.  

These two products reduce the amount of seed 

produced after application.  Clopyralid, dicamba, 

MCPA, picloram, and 2,4-D do not appear to 

reduce seed production after application if the 

plant has bolted.  Apply metsulfuron and 

chlorsulfuron in the spring, during bolting.  If the 

season is long and the musk thistles bolt the first 

year, apply metsulfuron and chlorsulfuron in the 

fall.  This same treatment can be used on bull 

and scotch thistle as well.  Always follow 

labeled directions; it’s the law! 

Information herein is offered with no discrimination.  

Listing a product does not imply endorsement by the 

authors, University of Nevada Cooperative Extension 

(UNCE) or its personnel.  Likewise criticism of products 

or equipment not listed is neither implied nor intended.  

UNCE and its authorized agents do not assume liability for 

suggested use(s) of chemical or other pest control 

measures suggested herein.  Pesticides must be applied 

according to the label directions to be lawfully

 

and 

effectively applied. 

References 

1)  Bussan, A.J., S.A. Dewey, M.A. Trainor and 

T.D. Wilson (eds).  2001-2002 Weed 

Management Handbook.  Extension Services 

of Montana, Utah and Wyoming.  pp. 81, 82, 

118, 226, 237, 279. 

2)  Rees, N.E., E.M. Coombs, L.V. Knutson, 

G.L. Piper, P.C. Quimby, Jr., N.R. Spencer, 

C.E. Turner.  1996.  Biological Control of 

Weeds in the West.  Oregon Department of 

Agriculture. 

3)  Sheley, R.L. and J.K Petroff.  1999.  Biology 

and Management of Noxious Rangeland 

Weeds.  Oregon State University Press.  

Corvallis, OR.  pp. 145-161. 

 

 

 

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 

 

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Editing by Sue Strom 

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