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 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 , 413 p. Turf weeds. Bull Thistle. Department of Crop and Soil Sciences, Michigan State University and Ronald Calhoun. Graham, Jessica. Identification and Management of Bull Thistle. University of Nevada Cooperative Extension. Fact Sheet Bull Thistle. Wanted Dead Not Alive. Nevada Project Weeds. Fact Sheet Bull Thistle. Center for Invasive Species and Ecosystem Health.