Other Scientific Names:
Carduus pycnocephalus L. subsp. cinereus (M.Bieb.) P.H.Davis; Carduus arabicus Jacq. subsp. cinereus (M.Bieb.) Kazmi
Other Common Names: Spanish thistle
Weed class: A
Year Listed: 2021
Native to: Turkey and east to the Himalayas
Is this Weed Toxic?:
not known to be
Why Is It a Noxious Weed?
Turkish thistle is documented as spreading on its own in Oregon and Idaho, competing with and crowding out native vegetation and desirable forage plants. It has been noted to spread readily and be competitive in native rangelands in NE Oregon. Other Carduus species are known to be weedy and invade rangelands, meadows, pastures, and fields in Washington and the Pacific Northwest. So far, Turkish thistle is not known to occur in Washington but it is spreading close by in Oregon and Idaho and could readily invade here.
How would I identify it?
Turkish thistle is an annual thistle with winged stems that can grow up to 4 feet tall. Its basal leaves are up to 4 inches long, and stem leaves reduce in size moving up the stem. Flower heads are compressed, non-spherical, and single or in loose clusters. Each purplish flower head is typically on a short hairy stem or may be stemless.
The flower heads are non-spherical, somewhat compressed, and narrow towards the purplish flowers. They occur singly or in loose groups of 2 to 5. A key identifying trait is that the flower heads are often on short stems (pedunculate). These flower head stems are 0 to 1.2 inches (0 to 3 cm) long and are covered in woolly hairs.
Turkish thistle plants have basal leaves and stem leaves. The basal leaves taper to winged petioles and are up to 4 inches long and have lobed edges (2 to 5 lobes). The undersides of the leaves are tomentose (with woolly hairs) while the upper surfaces are loosely woolly. The stem leaves attach directly to the stem and reduce in size going up the stems toward the tips.
Turkish thistle stems can vary greatly in size depending on habitat conditions, growing from 3 to 48 inches tall. Stems are winged, unbranched to openly branched, and loosely covered with soft woolly hairs.
Fruit Seed Description
Each seed is golden brown to brown in color, 0.16 to 0.24 inches long, and has a bristly tuft (pappus) at one end.
May Be Confused With
Of the five other Carduus species known to occur in North America, four are listed as noxious weeds in Washington State: Class A noxious weed Italian thistle (Carduus pycnocephalus), Class A noxious weed slenderflower thistle (Carduus tenuiflorus), Class B noxious weed plumeless thistle (Carduus acanthoides), and Class B noxious weed musk thistle (Carduus nutans). Slenderflower, Italian, and Turkish thistles all have more slender, compressed, non-spherical flower heads, while plumeless and musk thistle have more rounded, hemispherical flower heads.
Italian thistle is only documented from one location in Washington State, in Clallam County, but is known from a number of locations in Oregon and Idaho. Contact the State Weed Board or your county noxious weed control board for identification assistance.
Where does it grow?
As of 2020, Turkish thistle has not been documented in Washington State. Turkish thistle plants have been found in Oregon and Idaho, growing on canyon grasslands, which include scattered shrubs and trees, and are often dominated by native bunchgrasses. Turkish thistle grows on dry rocky talus slopes on southern aspects as well as sites with deeper soils in more mesic sites. Plants also grow along ephemeral streams, following their edges downhill.
How Does it Reproduce?
Turkish thistle reproduces by seed, it is not known to spread vegetatively.
How Do I Control It?
It is expected that control methods used on the other non-native Carduus species should be effective to manage and control Turkish thistle. Turkish thistle’s short growing season and its current distribution in hard to access locations makes it challenging to time control methods when they are most effective.
When possible, carry out control methods when pollinators are not active on plants. Also, make sure to clean shoes, clothing, and equipment when leaving infestations to prevent spreading seeds to new locations.
Many of the control methods from DiTomaso et al. (2013) for Carduus species can be used for Turkish thistle: https://wric.ucdavis.edu/information/natural%20areas/wr_C/Carduus_acanthoides-nutans-pycnocephalus-tenuiflorus.pdf
Currently Turkish thistle is not known to occur in Washington, contact your county noxious weed control board if you think you have Turkish thistle on your property.