Europe and Asia
Musk, or nodding thistle
is an aggressive, biennial herb with showy red-purple flowers and painful
spiny stems and leaves. Mature plants range in height from 1½ to
6 feet tall, and have multi-branched stems. Leaves are dark green,
coarsely lobed, with a smooth waxy surface and a yellowish to white spine
at the tip. The large disk-shaped flower heads, containing hundreds
of tiny individual flowers, are 1½ to 3½ inches in length and
occur at the tips of stems. Flower heads will droop to a 90-degree
angle from the stem when mature, hence its alternate name, nodding thistle. Each
plant may produce thousands of straw-colored seeds adorned with plume-like
Because musk thistle
is unpalatable to wildlife and livestock, selective grazing leads to severe
degradation of native meadows and grasslands as wildlife focus their foraging
on native plants, giving musk thistle a competitive advantage. Although
musk thistle is infrequently found in dense forests, it can colonize areas
subjected to natural disturbances such as landslides or frequent flooding. Meadows,
prairies, grassy balds, and other open areas are susceptible to invasion.
IN THE UNITED STATES
Musk thistle is found throughout the U.S. except
for Maine, Vermont, Florida, Alaska and Hawaii.
HABITAT IN THE UNITED STATES
grows from sea level to about 8,000 ft elevation, in neutral to acidic soils. It
invades open natural areas such as meadows, prairies, and grassy balds. It
spreads rapidly in areas subjected to frequent natural disturbance events
such as landslides and flooding but does not grow well in excessively wet,
dry or shady conditions.
A native of western Europe,
musk thistle was introduced into the eastern United States in the early 1800s
and has a long history as a rangeland pest in the U.S. It was first
discovered in Davidson County, Tennessee in 1942 and has been declared a
noxious weed in many states, including North Carolina.
BIOLOGY & SPREAD
Musk thistle is
usually a biennial, requiring 2 years to complete a reproductive cycle, but
may germinate and flower in a single year in warmer climates. Seedlings
emerge in mid to late July and develop into a rosette where plants can reach
4 feet in diameter. Plants overwinter in the rosette stage until they
begin to bolt in mid-March. During the bolting stage plants form multi-branched
stems to a height of 6 feet. The number of seedheads per plant is site-dependent
and ranges from about 24 to 56 on favorable sites and 1 to 18 on less favorable
sites. Flowers emerge in early May to August and seed dissemination
occurs approximately one month after the flowers form. A single flower
head may produce 1,200 seeds and a single plant up to 120,000 seeds, which
may be wind blown for miles. Seed may remain viable in the soil for
over ten years, making it a difficult plant to control.
and chemical methods are some of the effective methods available for control
of musk thistle.
Mechanical and Manual
Hand pulling is most
effective on small populations and can be done throughout the year, but is
prior to the development
of seeds. Flowers and seedheads should be bagged and disposed of
in a landfill to prevent or minimize seed dispersal. Minimizing disturbance
to the soil during removal activities will help reduce the chance of germination
of seeds stored in the soil.
Two weevils have
been introduced from Europe and released in the United States as a biological
the thistlehead-feeding weevil (Rhinocyllus conicus) and the rosette
weevil (Trichosirocalus horridus). These weevils have been released
in a number of western states with some notable successes achieved. However,
recent observations of unintentional and unanticipated impacts of the thistlehead-feeding
weevil to native thistles, including some rare species, has raised a red
flag about its continued use, at least in the western U.S.
Foliar spraying is effective on established
populations of musk thistle. Apply a 2% solution of glyphosate (e.g.,
Roundup®) or triclopyr (e.g., Garlon) and water plus a 0.5% non-ionic surfactant
wetting all leaves and stems. Chlorpyralid (e.g. Transline) is
effective at a concentration of 0.5% and is selective to Aster, Buckwheat,
and Pea families. A low pressure and coarse spray pattern will limit drift
and damage to non-target species. Treatments should be applied during
the rosette stage or prior to flowering. glyphosate is a non-selective
systemic (i.e., moves through the plant) herbicide that can kill non-target
plants that are only partially contacted by spray. Triclopyr is selective
to broadleaf species and is a better choice if native grasses are present.
USE PESTICIDES WISELY: ALWAYS READ THE ENTIRE PESTICIDE LABEL CAREFULLY, FOLLOW ALL MIXING AND APPLICATION INSTRUCTIONS AND WEAR ALL RECOMMENDED PERSONAL PROTECTIVE GEAR AND CLOTHING. CONTACT YOUR STATE DEPARTMENT OF AGRICULTURE FOR ANY ADDITIONAL PESTICIDE USE REQUIREMENTS, RESTRICTIONS OR RECOMMENDATIONS.
NOTICE: MENTION OF PESTICIDE PRODUCTS ON THIS WEB SITE DOES NOT CONSTITUTE ENDORSEMENT OF ANY MATERIAL.
For more information on
the management of musk thistle, please contact:
- Kris Johnson, Great Smoky Mountains
National Park, Gatlinburg, TN
SUGGESTED ALTERNATIVE PLANTS
a popular ornamental in the U.S., suitable native alternatives for musk thistle
in the eastern U.S. might include butterfly weed (Asclepias
tuberosa), Joe-pye weed (Eupatorium dubium), black-eyed Susan
(Rudbeckia fulgida), ironweed (Vernonia noveboracensis), wild blue
phlox (Phlox divaricata) and many others. Many plants native to
the West are also available. Check with the native plant society in your
state for more suggestions.
Tom Remaley, Great Smoky Mountains National
Park, Gatlinburg, TN
Jil M. Swearingen, National Park Service, Washington,
Alison Dalsimer, Consultant, Legacy Resource
Management Program, Washington, DC
Susan Ross, Great Smoky Mountains National Park,
Beck, K.G., R G. Wilson, and M. A. Henson. 1990. The
effects of selected herbicides on musk thistle (Carduus nutans) viable
achene production. Weed Technology, 4:482-486.
Heidel, Bonnie. 1985. Carduus nutans:
element stewardship abstract. The Nature Conservancy, Arlington, VA.
Hull, A.C., Jr., J.O. Evans. 1973. Musk
thistle (Carduus nutans) an undesirable range plant. Journal
of Range Management 26(5):383-385.
Kok, K.T., W.W. Surles. 1975. Successful
biocontrol of musk thistle by an introduced weevil. Environ.
Lacefield, G.D., E. Gray. 1970. The life
cycle of nodding thistle in Kentucky. Bowling Green, KY: Department
of Agriculture, Western Kentucky University.
Lambdin, P.L., J.F. Grant. 1992. Establishment
of Rhinocyllus conicus (Coleoptera: Curculionidea) on musk thistle
in Tennessee. Ent. News 103(5):193-198.
Monks, D.W., M.A. Halcomb and E.L. Ashburn.
1991. Survey and control of musk thistle (Carduus nutans) in
Tennessee field nurseries. Weed Technology. 5:218-220.
Swearingen, J. 2009. WeedUS Database of Plants Invading Natural Areas in the United States: Musk Thistle (Carduus nutans). http://www.invasive.org/weedus/subject.html?sub=3011.
The Nature Conservancy. Musk
Thistle: Element Stewardship Abstract. In: Wildland Weeds Management & Research
Program, Weeds on the Web.
USDA, NRCS. 2009. The PLANTS Database (http://plants.usda.gov). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.
Plant Conservation Alliance, Alien Plant Working Group.