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Italian thistle. Photo Credit: Eric Coombs, Oregon Department of Agriculture, Bugwood.org -
Italian thistle flowers. Photo Credit: Mary Ellen Harte, Bugwood.org -
Italian thistle leaves. Photo Credit: Mary Ellen Harte, Bugwood.org -
Italian thistle rosette.
Also known as: Plymouth thistle, shore thistle, Italian plumeless thistle
Italian thistle is a winter annual that quickly overtakes pastures and rangelands. It is an early grower, flowering early in the summer which allows it to absorb moisture other forage plants and native plants desire.
Description:
| Life Cycle: | Annual (life cycle lasts one year), sometimes Biennial (life cycle lasts two years) |
| Early Detection and Rapid Response species: | Yes |
| Height: | Up to 6-8 feet (1.8-2.5 meters) |
| Leaf Description: | Leaves are green and have cobweb-like hairs on their underside. Each leaf is lobed and ends with a prominent thorn. |
| Fruit & Flower Description: | Flowers are purple and form cylindrical clusters at the end of each stem. There are bractsBracts Leaf-like structures below a plant’s flower. at the base of each flowerhead with stiff, upright spines. They produce brown seeds with hairs on one end. |
| Bloom Time: | May to June |
Habitat:
- It grows in dry, open areas such as meadows, pastures, rangelands, and roadsides.
Impact:
- Italian thistle crowds out more desirable forage and crop plants, as well as native plants.
- Large outbreaks can form a physical barrier that inhibits livestock from entering an area.
- Its height increases the risk of severe wildfires by creating readily available ladder fuels. This allows fire to quickly reach a habitat’s overstory.
What we’re doing about it:
- Italian thistle is a priority species for the Tualatin SWCD. As such, our Invasive Species Program has been actively monitoring and treating it throughout the watershed.
- If identified within Washington County, a specially trained crew can come out survey for Italian thistle. If found, the crew will treat the infestation for free.
What you can do about it:
- If you think you’ve found Italian thistle anywhere in Washington County, please report it to the Oregon Invasive Species Hotline.
- Sheep and goats can be used to graze on it. This is best done in fall when thistle is less spiny, making them more palatable to grazing animals.
- Hand-pulling individual plants can prevent further spread for smaller patches. Digging is easiest in the spring or fall before the plant flowers. Place all removed plant materials in a tied plastic bag and dispose of it in the trash – not the yard debris.
Look-alikes:
Italian thistle looks similar toseveral other invasive thistles including milk thistle (Silybum marianum) and creeping thistle (Cirsium arvense). The best way to tell these species apart is by examining their flowers – Italian thistle’s flowers have spiny bracts at their base whereas the other species do not.
Noxious Weed Listing:
| State of Oregon: | Class B |
| State of Washington: | Class A |
More Resources:
Download the Italian Thistle Best Management Practices Factsheet
- Pacific Northwest Weed Management Handbook: Italian thistle
- University of California, Weed Research & Information Center: Italian thistle