Identification:C. vulgare is a biennial cool-season broadleaf that forms large, coarse plants with spiny leaves, large taproots, and stems that are heavy and branched at the top. C. vulgare can attain a height of six feet and produces very attractive purple flowers, approximately one to two inches in width. During the first year, the bull thistle forms a thorny rosette or cluster of leaves near the ground. The second year is marked by the production of flowers and subsequent “thistle down” or achene. The achenes are the wind disbursed seeds of C. vulgare. The leaves of C. vulgare are three to six inches long, alternating, have long spines, are toothed (double dentate) and have prickly hair above and cottony hairs below. The stems of C. vulgare are erect and contain many spreading branches that are green to brownish. Another distinctive feature of the C. vulgare stem is the cobweb like hairs that are usually found in the upper portion of the stems. C. vulgare is commonly confused with the Musk or Nodding thistle but is distinguished by noticing that the Musk thistle has a nodding head whereas C. vulgare has an erect head.
Original Distribution: Unfortunately, the exact site of initial distribution of C. vulgare has not been determined or at least documented. However, it has been inferred that the original distribution of C. vulgare was in the Northern hemisphere and most likely Europe although some literature also refers to Eurasia. It is thought that C. vulgare was carried to the United States by early settlers in the early 1800s either for ornamental purposes or as seed contaminants. The flowers are desirable to some gardeners as they attract birds and butterflies. In particular, hummingbirds frequent C. vulgare and many settlers desired hummingbirds in their gardens. Even today, C. vulgare is purposefully planted in gardens to attract birds and butterflies.
Current Distribution: From Europe, and possibly Eurasia, C. vulgare has established itself throughout the world. C. vulgare is currently distributed throughout the 48 contiguous states of the United States as well as Canada, Argentina, Hawaii, New Zealand and South Africa.
Site and Date of Introduction: While the exact site and date of introduction has not been determined, it is thought that the Bull Thistle was introduced to the United States by European Settlers in the early 1800s.
Mode(s) of Introduction: Information regarding the mode of introduction of C. vulgare is very limited. The general consensus is that the Bull thistle was brought to the United States by way of European Settlers who wanted to attract birds and butterflies to their gardens. Today, the mode of introduction into new areas occurs by means of intentional and unintentional human transport as well as by the achene, wind dispersed seeds, produced by the thistles.
Reason(s) Why it has Become Established:C. vulgare has a wide range of niches which include rangelands, pastures, meadows, old fields, poor soils, and disturbed sites in addition to the comfortable gardens they are intentionally introduced into. The Bull Thistle also thrives along roadsides and areas that have been disturbed affording the Bull Thistle an abundance of niches that can sustain its production. In addition, a mature bull thistle creates upwards of 10,000 seeds per year many of which remain dormant in the ground, for years, waiting for conditions to be just right before dispersing into the environment. While many seeds do remain in the ground, many more are wind dispersed which has proved to be extremely effective in aiding in the expansion of the Bull Thistle. Many native species, especially in New Jersey, have been overtaken by invasives such as phragmites which further allows the successful establishment of Bull Thistle as there are few native species left to suppress the germination of this noxious weed.
Ecological Role: As previously mentioned, the bull thistle does attract birds and butterflies. C. vulgare also produces an attractive purple flower that many people find to be desirable additions to their gardens. However, the Bull Thistle is covered with many spikes that cause local predators, such as deer, to avoid the areas in which C. vulgare grows. In an attempt to harvest Bull Thistle, I was unavoidable pricked many times by the numerous spikes on these weeds. These spikes cause considerable discomfort and are an effective deterrent to predators. The Bull Thistle also displaces indigenous plant species and makes attempts to enter the area for grazing difficult and painful which, in turn, limits the biodiversity of the area in which it grows.
Benefit(s): Bull Thistles have very attractive purple flowers that some individuals desire to enhance the beauty of their gardens and attract butterflies and birds. In particular, hummingbirds frequent C. vulgare and many gardeners desire the visitation of hummingbirds to their gardens. The Bull thistle is also effective in keeping undesirable predators away from areas that it inhabits as the thistle contains many thorns which are painful to walk on and eat. C. vulgare is also undesirable as a food source for predators as it does not seem to be palatable to the local predators that have encountered C. vulgare.
Achene seed example
C. vulgare thorny rosette
hreat(s): The Bull Thistle poses the threat of displacing native species of plants and limiting local biodiversity in the environments where it is established. Bull Thistle is very hardy and is a master at taking advantage of disturbed areas and varied environmental conditions so it has the potential to become a serious threat and is, in fact, considered serious in some parts of t he United States. The Bull thistle is a threat to native species primarily due to the distaste that predators have for C. vulgare and its ability to thrive in disturbed areas. This distaste, in addition to the thorny nature of the plant, along with its ability to thrive in disturbed areas as well as rangelands, pastures, meadows, old fields, poor soils and gardens, gives C. vulgare an advantage over other species. C. vulgare out competes its neighbors, which predators are happy to eat and which have limited ranges, by establishing itself in an area and removing its competitor’s predators which may also be their seed dispersers. As a result, indigenous species may become suppressed, if not locally extinct, due to the establishment of C. vulgare in an area. C. vulgare is also a threat because it is so difficult to control. Their achenes are readily dispersed via the wind and it is difficult at best, if not impossible, to try to contain their dispersal. So many achenes are released that the only way to avoid their dispersal is to bag the flowers of C. vulgare and burn them before they can release their achenes. However, a mature bull thistle creates upwards of 10,000 seeds per year many of which remain dormant in the ground, for years, waiting for conditions to be just right before dispersing into the environment. Therefore, even if you bag and burn all the flowers you see, the chances are great that dormant seeds will germinate and repopulate the controlled area. Also, harvesting Bull Thistle is not as easy as it sounds as they are prolific and very difficult to harvest due to their spikes.
Control Level Diagnosis:“Medium Priority.”C. vulgare has already established itself quite well in most of the United States. The potential for the spread of this weed is considerable as its roots are strong and its seeds can lie dormant for many years before awakening when conditions are suitable for their establishment. The Bull Thistle is a weed that should be eradicated in the United States as it has the ability to decrease biodiversity by displacing local species and predators.
Control Method: The control methods for Bull Thistle seem to be failing miserably but efforts are still underway to eliminate the weed in many areas of the United States. For instance, Oklahoma has set up a website advising people to call environmental authorities if the weed is discovered. Oklahoma has also launched a public relations campaign against the Bull Thistle and has offered advice to its residents on eradication methods available. Oklahoma has gone so far as to create an “Oklahoma Thistle Law” which “requires all landowners to prevent the seed production of Bull Thistle on their land” (Stritzke). The Oklahoma department of agriculture is required to perform an annual thistle survey and subsequently provide control recommendations with the goal of killing all the Bull Thistles and their seeds in the soil. Some of the control methods include: The “release of Musk thistle head and rosette weevils in protected areas (fence rows, road right-of-way, etc), Plant cover in fall and winter to provide competition, Spray pastures for 3-4 years to stop seed production, monitor weevil activity and shift away from spraying once thistles heads get eggs deposited on them” (Stritzke). In Chenango County, NY, a campaign is underway to change the status of the Bull Thistle as the official county flower because some individuals recognize its detrimental affects on the environment and would prefer a native species be adopted as the official county flower. The control method message in Chenango County is to cut the flowering heads of the Bull Thistle off and place them in a bag for subsequent burning. In fact, this control method is recommended in general as well since the seeds from the flowers disperse via the wind from the flowering head and cause the establishment of the species in other areas. In addition, to preventing C. vulgare from establishing itself, post emergence herbicides can be applied in mid spring and early summer. Hand removal has proven unsuccessful because of the enormous amount of seeds produced by one Bull Thistle as have biological controls such as insect introduction because it can take up to ten years for introduced insect populations to increase enough in size that they can become effective against this weed. In the Valles Caldera National Preserve, eradication methods are being proposed that would include spraying the plants with the herbicide clopyralid (Transline) but this control method must be carefully monitored and utilized.
Artmakers. Chenango County Dump the Bull Thistle Campaign. 15 Oct. 2004 <http://www.artmakers.com/bullthistle/>
Lym, Rodney G. and Richard Zollinger. Perennial and Biennial Thistle Control: Bull Thistle. Nov. 2000. North Dakota State University. 15 Oct. 2004 <http://www.ext.nodak.edu/extpubs/plantsci/weeds/w799w.htm>
Moran, Mark. Study of Northern Virginia Ecology: Bull Thistle Cirsium vulgare. Stratford Landing Elementary School. Fairfax County Public Schools. 15 Oct. 2004. <http://www.fcps.k12.va.us/StratfordLandingES/Ecology/mpages/bull_thistle.htm>
National Park Service. Bull Thistle Cirsium vulgare Sunflower family. 06 June 2001. 15 Oct. 2004. <http://www.nps.gov/redw/bullthis.htm>
Stritzke, Jim. Bull Thistle. Oklahoma State University.15 Oct. 2004 <http://alfalfa.okstate.edu/webnews/bullthistle.htm>