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 (Urophorastylata) 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