This information courtesy
of the Colorado Natural Areas Program
Family: Asteraceae (Composite)
Other Names:
common thistle, spear thistle, fuller’s
thistle
USDA Code:
CIVU
Legal Status:
Colorado Noxious Weed List B
IDENTIFICATION
Lifecycle:
Biennial
Growth form:
forb/herb
Flower:
Flowers are 1.5-2 inches wide and clustered at
the ends of branches. The flower bracts are somewhat tapered
and covered with spines (Whitson et al. 1996). Flowers are
pinkish to dark purple.
Seeds/Fruit:
Seeds are capped with a circle of plume-like
white hairs.
Leaves:
Leaves are alternate. Bull are the only thistles
in Colorado that are prickly hairy on the top surface of the
leaves. They are cottony-hairy on the undersides.
Stems:
In mature plants the leaves extend down, clasping
the stem and are divided into segments (i.e. strongly
decurrent).
Roots:
Has a short, fleshy taproot with several primary
roots extending from the root crown. Each bears a number of
smaller lateral roots.
Seedling:
Seed leaves (cotyledons) are round to spatulate,
and smooth. First true leaves are oval to spatulate with spines and a rough, bumpy surface
(Carey et al. 1993). First year plants form a rosette with
leaves easily distinguished from other thistles by the above
leaf characteristics.
SIMILAR SPECIES
Exotics:
Could be confused with musk thistle.
Natives:
There are many native Cirsium species, some
common (like Cirsium undulatum) some rare (like Cirsium
perplexans). The natives generally do not have leaves
clasping the stem all the way from node to node (strongly
decurrent leaves), and many have hairy upper and lower leaf
surfaces and are blue-green or gray in color.
IMPACTS
Agricultural:
Heavy infestations can exclude livestock
from areas. Additionally, the presence of bull thistle in
hay decreases the forage value and lowers the market price
(Zimmerman 1997). It is an aggressive weed, but it will not
survive where cultivation has cut back its stem and
destroyed its root system (FEIS 1998).
Ecological:
Bull thistle is often a transient species,
appearing in recent clear cuts or disturbed areas and
becoming a dominant species for several years (Rees et al.
1996)
Human:
Bull thistle has been reported to cause hay fever
in some individuals (FEIS 1998).
HABITAT AND DISTRIBUTION
General requirements:
Bull thistle grows in dry to moist
habitats. It thrives on nitrogen-rich soils, and it grows on
gravelly to clay-textured soils. Bull thistle cannot
withstand deep shade, and is nearly absent if light is
reduced to less than 40% of full sunlight (FEIS 1998).
Potential habitats include pastures, overgrazed rangeland,
roadsides, and logged areas.
Distribution:
Within Colorado bull thistle infestations
have been reported to occur in nearly all counties west of
the continental divide, this plant has also been observed in
the Upper Arkansas Watershed and in pockets on the plains.
It is widespread throughout the United States and parts of
Canada.
Historical:
Bull thistle was introduced to North America
as a seed contaminant and is now widespread.
BIOLOGY/ECOLOGY
Life cycle:
Biennial
Mode of reproduction:
Seed
Seed production:
Mature plants can produce up to 4,000
seeds per plant (Zimmerman 1997).
Seed bank:
Seeds have little dormancy, and germinate
rapidly whenever conditions are favorable, usually in the
spring and fall (FEIS 1998). Although most of the seeds on
or near the surface do not remain viable for more than a
year, seeds that are buried at a depth of 5 inches may
remain viable for up to three years (Zimmerman 1997).
Dispersal:
Seeds are capped with a circle of plume-like
white hairs and can be windblown for long distances.
However, it has been found that 65% of the seeds land within
two meters of the parent plant (Zimmerman 1997).
INTEGRATED MANAGEMENT SUMMARY
Bull thistle does not tolerate shade and therefore does
not compete well in areas that are populated by tall grasses
and forbs. Improving the health of a natural area, and
guarding against disturbance or overuse, can be a good
preventative measure against bull thistle. Chemical control
is most effective when rosettes are targeted (fall or spring
depending on population density and the plant’s stage of
growth). Mechanical controls can be used to eliminate small
populations or plants in a later growth stage. To be
effective plants with buds or flowers should be collected
and immediately either landfilled or destroyed in a method
that eliminates seeds. Do not cut or spray if your
management program is relying on seedhead biological control
organisms (local or state rules may disqualify the use of
biological control).
REFERENCES
Calweed Database. 1997. California Noxious Weed
Control Projects Inventory. Natural Resource Projects
Inventory, Information Center for the Environment,
University of California, Davis. Available: http://endeavor.des.ucdavis.edu/weeds/
Carey, J. Boyd, James J. Kells, and Karen A. Renner.
1993. Common Weed Seedlings of Michigan. Department
of Crop and Soil Sciences Michigan State University
Extension Bulletin E-1363. Internet 10/27/99. Available:
http://www.msue.msu.edu/msue/iac/e1363/e1363.htm
Colorado Natural Areas Program. 2000. Creating
an Integrated Weed Management Plan: A Handbook for Owners
and Managers of Lands with Natural Values.
Colorado Natural Areas Program, Colorado State
Parks, Colorado Department of Natural Resources; and
Division of Plant Industry, Colorado Department of
Agriculture. Denver, Colorado. 349 pages.
FEIS - Fire Effects Information System [Online] (1996,
September). Prescribed Fire and Fire Effects Research Work
Unit, Rocky Mountain Research Station (producer), US Forest
Service. Available: www.fs.fed.us/database/feis/ [1998,March
12]
Rees, N.E., P.C. Quimby Jr., G.L. Piper, E.M. Coombs, C.E.
Turner, N.R. Spencer, and L.V. Knutson (editors). 1996. Biological
control of weeds in the west. Western Society of Weed
Science in cooperation with USDA Agricultural Research
Service, Montana Department of Agriculture, and Montana
State University.
USDA, NRCS. 2005. The PLANTS Database, Version 3.5
(http://plants.usda.gov). Data compiled from various sources
by Mark W. Skinner. National Plant Data Center, Baton Rouge,
LA 70874-4490 USA
Whitson, T.D.(ed.), L.C. Burrill, S.A. Dewey, D.W. Cudney,
B.E. Nelson, R.D. Lee, R. Parker. 1996. Bull thistle. Weeds
of the West. Western Society of Weed Science, in
cooperation with the Western United States Land Grant
Universities Cooperative Extension Services, Newark CA. pg.
118.
Zimmerman, J.A.C. 1997. Ecology and distribution of
Cirsium vulgare (Savi) Tenore, Asteraceae. USGS Southwest
Exotic Plant Mapping Program. Internet 1/21/99. Available:
http://www.usgs.nau.edu/swemp/
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