We have plenty of thistles growing in our area and landowners across the region are working hard to combat these prickly invaders. While most of the thistles growing in our area are invasive, some of them are actually native. Unfortunately, a recent discovery from eastern Oregon marks the addition of a new invasive thistle to the state.
This spring, the Oregon State Weed Board approved the addition of a new invasive thistle, known as welted or curly plumeless thistle (Carduus crispus) to the Oregon Noxious Weed list. Welted thistle was recently discovered at one location in Wallowa County. Prior to this discovery it was known from limited to sites in North Dakota and British Columbia. With this very limited distribution, this new noxious weed is high priority for control and eradication.
The Oregon Department of Agriculture describes as follows:
Welted thistle is a native to Europe and Asia. It can grow as an annual or biennial, 30–150 cm tall depending on growing conditions. Stems are openly branching, hairy with curled hairs to nearly smooth. Stems have spiny wings to 1.5 cm wide, and sport wing spines 3 mm long. The leaves have winged petioles at their base. Leaf blades are 10–20 cm long with spiny-toothed margins. Flower heads are borne singly or in groups of 2–5, 15–18 mm wide. Flower peduncles are spiny-winged to near apex or throughout, to 4 cm wide. Flower corollas can be either purple or white. Flower parts are both male and female. Flowering occurs July through September. Insect pollination is required. Reproduction is entirely by seed. The first record of welted thistle occurred in the Eastern U.S. in 1974. In 2016, a new western infestation was detected in Wallowa County, Oregon. Carduus crispus closely resembles the more common C. acanthoides (plumeless thistle).
For more information about welted thistle check out the Oregon Department of Agriculture’s Welted Thistle Risk Assessment.
Learn more at the WeedWise welted thistle weed profile page