Download Bull Thistle

Bull Thistle
Cirsium vulgare
Bull Thistle, an introduced and naturalized invasive
annual or biennial herbaceous plant that invades
disturbed areas throughout the United State. Bull
Thistle can invade almost any type of disturbed area,
from forest clear-cuts to riparian areas to pastures
where it can form dense thickets displacing other
vegetation. The spiny nature of the plant renders it
unpalatable to wildlife and livestock and reduces the
forage potential of pastures. Bull Thistle is native to
Europe, western Asia, and northern Africa. It is
thought to have been introduced to the eastern United
States during the colonial times and the western
United States in the late 1800s. It is currently found in
all 50 states.
Habitat: Disturbed sites; prairies, marshes, roadsides.
Leaves: Very spiny, pinnately divided into segments
that can be lobed then toothed.
Bull Thistle has a large purple flower
Flowers: Head purple, 1 1/2"-2" wide, bracts with
spiny tips; inflorescence of several heads; blooms June-Oct.
Stems: The tall, spiny, winged stems (up to 7 feet tall)
have many spreading stems.
Reproduction: By seed and rhizomes.
Control: Encouraging the development of healthy,
dense native prairie vegetation can help prevent and
reduce Canada thistle. A buffer zone free of Canada
thistle should be maintained near important natural
areas to prevent invasion. Plants within wind
dispersal range of a site about to undergo restoration
should be controlled prior to commencing work.
Manual or Mechanical Control: In a high-quality
natural area, repeated mowing or selective cutting
close to the ground can reduce an infestation within
three to
The spines of Bull Thistle make it
unpalatable for wildlife and
livestock
four years. Use a scythe or other sharp tool for
selective cutting. The ideal time to cut or mow
Canada thistle is prior to the flower buds opening
because the plat’s food reserves are at their lowest
point and seeds have yet to form. Cutting and
mowing should be done at least three times during
the growing season (June through September).
Mowing after flowering will only spread the seed.
Mowers should be cleaned if used in areas with
thistle in seed. Plants cut eight of more days after
flower have opened should be collected and
removed from the site to prevent seed
development form progressing. Cutting new
shoots every twenty to thirty days for tow or three
seasons can reportedly eradicate individual
populations.
It is much easier to eradicate Bull Thistle
when it first appears
Early spring burns tend to increase
sprouting and reproduction. Late spring burns
may discourage established Canada thistle plants but may also encourage further seed
germination. Burns may, therefore, need to be conducted for three consecutive years.
Chemical Control: Control of this species with
herbicides in high-quality natural areas is not
recommended because herbicides can cause
more damage to native vegetation than the
damage caused by Canada thistle. In other
areas, Clopyralid or metsulfuron-methyl have
been used effectively as foliar sprays.
Researchers report good results form using a 12% a.i. solution of glyphosate during the early
bolting stage when plants are 6-10 inches tall,
during the bud to flowering stage, or when
applied to rosettes in the fall. Remember that
glyphosate is nonselective and will kill or harm
any green plant that it contacts.
Spot applications to control individual
plans or stems are most effective with a wick
applicator or hand sprayer using either
Clopyralid or glyphosate.
You can spot Bull Thistle in the winter, and
then make a map of where it is on your
property