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/2003/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 06-22 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