Bull Thistle Cirsium vulgare
Introduction of Bull Thistle
• Bull thistle is native to Europe, western Asia
and North Africa.
• Bull thistle was introduced in western North
America via overseas shipping through
Portland, OR, in the late 1800s.
• Bull thistle was common in Arizona, California,
Colorado, Nevada, Oregon, Utah, Washington
and Wyoming by 1900.
Distribution in Nevada
• Found in all counties
of Nevada
• Most common thistle
found on rangelands
• Least serious of the
invasive thistles
Other Thistles on Rangelands
• Other common invasives- Scotch thistle, Canada
thistle, perennial sowthistle, and Musk thistle.
• Common native thistles- Anderson’s thistle,
Snowy thistle, Douglas thistle.
• Plants can be identified by flower color, bract
shape, leaves, and stems.
• See
http://www.unce.unr.edu/publications/files/nr/200
3/FS0351.pdf
Identifying Thistles in the Field
• Difficult to identify every thistle species
correctly i.e. there are many different species.
• When in the field: Carry weed ID book, shovel,
and camera. Try to identify plant and if cutting
works, cut it down.
• If you don’t know for sure: Take up close
pictures, mark location, and at the office
identify plant. Plants don’t run away, you can
always go back later.
Range of Bull Thistle
• The plant thrives in moist soils and is less
common on sand and pure clay soils.
• Typical habitats include disturbed or degraded
land, such as roadsides, fence rows,
overgrazed pastures and rangelands, eroded
gullies, ditch banks and vacant lots.
• Bull thistle grows best on soils that are rich in
nitrogen. (i.e grazed pastures) and have a
neutral pH
Range continued…
• Bull Thistle does not grow well in shade or
under droughty conditions.
• In Nevada, riparian areas are a common place
that Bull Thistle is found.
Life History of Bull Thistle
• Bull thistle is a biennial
• Bull thistle leaves are hairy on top
• The flower bracts have spines.
• Bull thistle has a short taproot
that does not creep or spread.
Life History continued
• Produces from 5,000 seeds up to 50,000 seeds
on very vigorous plants. Numerous seedheads
Dispersal
• Most common dispersal is through infested
agricultural products such as hay.
• On rangelands they disperse effectively via:
• Wind
• Water
• Grazing animals(especially in pastures).
Impact of Bull Thistle
• Undesired vegetation; cattle won’t graze it
because of the spines and low quality.
• Allowed a competitive advantage
• Invades riparian areas very effectively. Even
with high percent ground cover. i.e. little bare
ground.
• Eradication dollars often spent elsewhere on
different species (increased even more).
Competitive Advantages of Bull Thistle
• Not grazed by cattle because of spines
• Grazed pastures contain excess N which Bull
thistle is competitive at capturing.
• Produces lots of seeds
• Effectively disperses via different mechanisms
Management-Early Stages
• Active eradication in first year(before
seedhead develops). Cutting works best,
spraying is effective also.
• Burning-(farm field, pastures)
• Lag-Log factor- Difficult to control after
enough plants establish because of seed
numbers and dispersal factors.
• Isolate areas and avoid transportation via
vehicles, people, animals as much as possible.
Eradication and Management After
Maturity
• Requires devoting around five years in most
areas.( Deplete seed bank after initial
treatment, if dispersal occurs).
• Cutting/Mowing is effective if done before
seedhead development.
• Herbicide- Effective at killing plant.
• After seedset most control efforts only limit
dispersal distances but don’t prevent it.
• Efforts should be focused early in season.
Common Herbicides Used
•
•
•
•
•
Tordon( not approved for use in CA)
Telar
2-4-D
Can’t spray these on/near water
Rodeo is normally used in riparian areas, is
similar to roundup except it is safe to use in
and around water and riparian areas.
Management and Control Continued
• Must continue treatment yearly because of
seedbank.
• Establish native perennial grasses, sedges, and
rushes to compete.
• Avoid heavy grazing (i.e. riparian
management, rotational grazing).
• Biological control with seedhead fly (Urophora
stylata) has been effective in some states.
Fundamental Problem with Bull Thistle
• Limited control dollars= $$$ spent on the
most invasive species.
• Little money spent on Bull Thistle if it reaches
the point where control requires lots of time
and money.
What you can do??
• Cut Bull thistle plants if you find any in the
field (before infestation requires lots of time
and $$$$).
• Practice ecologically sound grazing and
riparian management.
• Manage for perennial riparian vegetation such
Carex and Juncus spp. that increases percent
cover of ground.
Citations
• Van Driesche, R., et al., 2002, Biological Control of Invasive Plants in the
Eastern United States, USDA Forest Service Publication FHTET-2002-04,
413 p.
• Turf weeds. Bull Thistle. Department of Crop and Soil Sciences, Michigan
State University and Ronald
Calhoun.http://www.msuturfweeds.net/details/_/bull_thistle_19/
• Graham, Jessica. Identification and Management of Bull Thistle. University
of Nevada Cooperative Extension. Fact Sheet. 05-03
• Bull Thistle. Wanted Dead Not Alive. Nevada Project Weeds. Fact Sheet 0622 http://www.unce.unr.edu/publications/files/ag/2006/fs0622.pdf
• Bull Thistle. Center for Invasive Species and Ecosystem Health.
http://www.invasive.org/species/subject.cfm?sub=3393