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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, slender 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: | 1 to 6 feet (15 – 200 centimeters) |
| Leaf Description: | Leaves are green and have cobweb-like hairs on their underside. Each leaf is lobed and ends with a prominent spine. |
| Fruit & Flower Description: | Flowers are purple and form cylindrical clusters and produce brown seeds with hairs on one end. There are bractsSmall leaf-like structures that are just below a plant’s flower. at the base of each flowerhead with stiff, upright spines. |
| Bloom Time: | May to June |
Habitat:
- Italian thistle grows in dry, open areas such as 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.
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.
- Deferring sheep grazing until the autumn is effective in reducing the density of Italian thistle stands. During the fall, Italian thistle becomes less spiny and sheep will graze it along with grasses.
- For smaller patches, hand-pulling individual plants can prevent further spread. Digging is easiest in the spring or fall before the plant flowers.
Look-alikes:
Italian thistle looks similar to a couple of other invasive thistles including milk thistle (Silybum marianum) and Canada thistle (Cirsium arvense). The best way to tell these species apart is by examining their flowers – Italian thistle’s flowers has spiny bracts at the base whereas the other thistle species do no.
Noxious Weed Listing:
| State of Oregon: | Class B |
| State of Washington: | Class A |
More Resources:
- Pacific Northwest Weed Management Handbook: Italian thistle
- University of California, Weed Research & Information Center: Italian thistle