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Creeping thistle flowers. Photo Credit: Jan Samanek, Phytosanitary Administration, Bugwood.org -
Creeping thistle flower. Photo Credit: Jan Samanek, Phytosanitary Administration, Bugwood.org -
Creeping thistle leaves. Photo Credit: Jan Samanek, Phytosanitary Administration, Bugwood.org -
Creeping thistle infestation. Photo Credit: Jan Samanek, Phytosanitary Administration, Bugwood.org
Also known as: Canada thistle, Canadian thistle, Californian thistle, corn thistle, field thistle
Chances are you’ve seen creeping thistle. This tall, prickly perennial is the most common thistle in the United States. Its extensive root system spreads quickly and can overtake large areas of pastures or fields in just one growing season.
Description:
| Life Cycle: | Perennial (life cycle lasts more than one year) |
| Early Detection and Rapid Response species: | No |
| Height: | Up to 5 feet (1.5 meters) tall |
| Leaf Description: | Lanced-shaped leaves grow alternately along the stem. The edges of the leaves are lobed and have yellow spines at their tips. |
| Fruit & Flower Description: | Pink to purple flowers grow in clusters at the ends of each stem. There are tiny bractsBracts Leaf-like structures below a plant’s flower. under each flowerhead that have weakly spined tips. It has male and female plants – both of which are needed to create viable seeds. Seeds are dispersed by the wind, clothing, or as a contaminate in seed or hay. |
| Bloom Time: | June to October |
Habitat:
- Creeping thistle is common in pastures and croplands. It also can be found in natural areas such as prairies and along streambanks.
- It typically grows in areas with an abundance sun and moist but not wet soils.
Impact:
- Creeping thistle competes with native plants and crops for moisture, nutrients, and light. Eventually it It can develop into large monocultures that are difficult to remove.
- It poses an economic threat to the agriculture industry by reducing crop yields.
- It spreads quickly by its extensive root system. In one season it can spread across a 10 – 12 foot (3 – 3.5 meter) area.
What you can do about it:
- It is difficult to control once it is established on a site. A combination of treatments may be needed to control dense stands.
- Hand pulling small patches effectively controls new infestations. However, larger infestations have established rhizomes which make this method extremely difficult and labor intensive.
- Dispose of all plant material in a tied plastic bag and throw it away in the trash – not the yard debris or home compost.
- Repeated mowing can prevent flowering and seed production but must be repeated for several years to be effective.
Look-alikes:
Creeping thistle looks similar to other invasive thistles, including bull thistle (Cirsium arvense). Creeping thistle’s flowerheads are smaller and the spines at the tip of its leaves are less pronounced than bull thistle’s.
Noxious Weed Listing:
| State of Oregon: | Class B |
| State of Washington: | Class C |
More Resources:
Download the Creeping Thistle Best Management Practices Factsheet
- Pacific Northwest Weed Management Handbook: Canada thistle
- University of California, Weed Research & Information Center: Canada thistle