The Enemy: Plumeless thistle (Carduus acanthoides L.) is a winter annual or biannual plant that can form dense patches in pasture, range, or disturbed sites. This state listed noxious weed has deeply lobed leaves and can grow to a height of 6 feet tall. Like its close relative Musk thistle (Carduus nutans), this plant has bright pink flowers only smaller ¾ to 1 inch in size. It does not have the silver outer margins on the leaves that Musk thistle has. It has a deep tap root, the stems have spiny wings, and the flower heads have spines on them as well.
The Strategy: This plant is a new invader to the area and is believed to have been brought in as an ornamental. Therefore, it has the potential to invade all the sites, even landscape and ornamental gardens. It is unpalatable to most animals and can quickly invade an entire meadow or pasture. This plant can be seen along the railroad tracks starting in Madison County and follows it all the way to the Montana border but has been seen in most counties in Eastern Idaho.
The Defense: As this is a biannual weed control can be simple. If you see one in your proximity, digging it up will kill it, making sure that at least a couple inches of root are dug out of the ground. It cases where there are abundance of the plants herbicides should be used. Products of choice may be Telar XP, Escort XP, Redeem, Milestone, or even Tordon 22K. Products such as Roundup Pro or 2,4-D are fairly ineffective. Idaho does not have an approved Biocontrol agent. Call your weed specialist for proper identification.
PLEASE NOTE – The proper use and application of herbicides can be an effective way to control and eradicate noxious and invasive plants. Before using herbicides, always carefully follow the label and safety instructions on the label. While we recommend the use of herbicides as one of the effective tools for integrated pest management, the Idaho Weed Awareness Campaign assumes no liability for herbicide applications.