Bull Thistle
Family
Cirsium vulgare
Designation/Status
Arizona Noxious Weed List -
Not Listed
Federal Noxious Weed List – Not Listed
Origins
Europe and Asia.
Plant Characteristics
Life Cycle: Biennial, grows 12-80 in.
the first year, the second year the stems grow to become woody and
branched.
Flowering begins in July and continues through August. Each plant has an average of 90 flower heads and can
produce approximately 25,000 seeds. Seeds can persist for many
years in the ground before germinating. Germination occurs in the
fall or spring.
Visual
Appearance: Purple disk flowers of large composite heads.
Leaves are long, sharp and deeply lobed, the base of the leaves
attach to the stem, spines appear on the upper surfaces and on the
tips. Only thistle that has spines on the surface of the
leaf.
Habitat
Low to mid elevations.
Prefers clearing and open pastures and other areas of disturbance,
right-of-ways, fence lines
Control Measures
Mechanical and Cultural:
Hand cut off plants at ground level before the flower heads turn
purple to stop seed production, any purple heads need to be
bagged, if not removed the heads will continue to germinate the
seeds. Tilling can eradicate rosettes that have established in the
preceding summer or fall.
Biological:
Trichosirocalus horridus,
feeds on the crown center of the rosette, it takes an average of
5-7 years for weevil populations to control thistle.
Other Points of Interest
Accidentally introduced during the 1800s from Europe.
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