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Bull thistle flowers. Photo Credit: Alex Katovich, Bugwood.org -
Bull thistle flowers. -
Bull thistle flower. Photo Credit: Kenneth M. Gale, Bugwood.org -
Bull thistle leaf. Photo Credit: Steve Dewey, Utah State University, Bugwood.org -
Bull thistle rosette. Photo Credit: Michael Shephard, USDA Forest Service, Bugwood.org
Also known as: Fuller’s thistle, common thistle, spear thistle
Bull thistle is a widespread biennial thistle that can be found throughout North America. Although it is intimidating in appearance, it is not as challenging to control as other thistles and is mainly a problem in hay fields and pastures.
Description:
| Life Cycle: | Biennial (life cycle lasts two years) |
| Early Detection and Rapid Response species: | No |
| Height: | 3 to 6 feet (1 – 2 meters) |
| Leaf Description: | During its first year, bull thistle forms a rosette with green leaves with deeply lobed edges. During its second year, it has similar leaves that grow alternately along the flowering stem and has sharp spines at their tip. |
| Fruit & Flower Description: | Flowers are dark purple and grow in gumdrop-shaped flowerheads that may occur by themselves or in clusters of two or three at the end of plant stems. |
| Bloom Time: | July to September |
Habitat:
- Bull thistle is commonly found in disturbed areas such as pastures, roadsides, logged forest areas, and hayfields
- It prefers sunny, open areas but can tolerate a wide range of conditions, from moist to dry soils.
Impact:
- Bull thistle outcompetes native plants and desirable livestock forage plants.
- The presence of bull thistle can cause hay prices to decline.
What you can do about it:
- Bull thistle reproduces by seed so preventing seeds from spreading is key to stopping new infestations.
- Contaminated hay is a primary means of spreading seeds, be careful to purchase weed-free hay.
- For smaller patches, hand-pulling individual plants can prevent further spread. Digging is easiest in the spring or fall before the plant flowers.
- For flowering plants, remove any flowers or seeds and place them in a plastic bag before you dig the plant up. Make sure to throw the plastic bag away in the trash.
Look-alikes:
Bull thistle looks similar to other invasive thistles, including Canada thistle (Cirsium arvense). Bull thistle’s flowerheads are larger and the spines at the tip of its leaves are more pronounced than Canada thistle’s.
Noxious Weed Listing:
| State of Oregon: | Class B |
| State of Washington: | Class C |
More Resources:
- Pacific Northwest Weed Management Handbook: Bull thistle
- University of California, Weed Research & Information Center: Bull thistle