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Key identifying traits
Abundant upper branching gives "top heavy"
appearance to mature plants or old dead plants
Spiny wings extend entire length of stems, right up to flower
heads
Flowers about 1 inch across and purple
(generally)
Bracts surrounding the flower are narrow, appearing as sharp
spines
Stem leaves are alternate and blend into stems
Older rosettes have deeply lobed, wavy leaves with yellow
spines along white leaf margins
Biology and ecology
- A winter annual or biennial with a tap root
- Reproduces by seed only
- Found in pastures, fields and roadsides
- Mature plants normally grow 3-6 feet tall but are known to
grow as tall as 8 feet in our area
- Flowering occurs June to August
- Can dominate sites to exclusion of livestock
- Can hybridize with Musk thistle
Control
Prevention – Learn to
identify plants; know your property; beware of fill dirt, hay and
seed from outside your area
Biological – Some established and effective in the county
reducing seed production and plant density
Cultural – Good vegetative cover tends to inhibit
establishment but it can invade healthy sites
Mechanical – Regular cultivation, digging or cutting are
effective because of seed only spread
Chemical –Several effective at label rates when applied
at vegetative stage either in the first or second year of
lifecycle (spring/fall).
Refer to the
PNW Weed Management Handbook for specific chemical recommendations |
flower heads with spiny stems
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