Idaho Weed Awareness Campaign
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Musk Thistle                                     

The Enemy - Musk thistle (Carduus nutans) is a biennial weed that invades any piece of property that can be found. It is the tall thistle with a baseball size flower head. Also called Nodding thistle it forms a rosette the first year and then sends up 1 to 6 vegetative upright extensions (up to 6 foot tall) that produces a terminal pink flowers. Secondary growth extensions form from mid-length produce flowers as well. These seed heads will always be flat on the bottom and have bright pink flowers. The rosette leaves are serrated with white outer margins.

The Strategy - This plant is very invasive. It spreads by wind which allows it to travel onto adjacent lands. Its rosette can get 3 feet in diameter which allows it to shade desirable plants and rob the soil of needed nutrients. Being a thistle the plant hosts many sharp points that makes it so no animal wants to pass close to it.

The Defense - As with most annual and biennial plants it can be controlled with a shovel. Ensure that you get at least 4 inches of the root or it will grow back. Also, loosen the soil by cutting into the soil and working in a circle; when you return to the starting point pry the shovel handle back and pull the plant out of the ground as to limit the amount of disturbed soil. The larvae from the Rhino beetle will eat the seeds in the top flower. The lower flowers are not affected as they bloom later, and it ensures viability to the future of the insects. Releasing the root feeding insects reduce the impact of the weed.

Dow LogoRoundup and 2,4-D are not effective on this plant except in the early spring or fall. Using advanced products such as Milestone or Chaparral® are very effective in controlling this weed.

Click to read this article "Control Musk Thistle and Plumeless Thistle on Rangeland, Pastures,
Roadsides and Conservation Reserve Program (CRP) Areas"

Link to Milestone label. Link to Chaparral label.

Tordon 22K, Curtail, Telar® XP and Escort® XP are effective as well. If the plant is bolting then let it grow until it reaches the bud stage. This will not harm any bio-control agents that are present.


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.

For more information, click on the link below to download the Idaho's Noxious Weeds Control Guidelines publication produced by the University of Idaho Extension.

U of I Idaho's Noxious Weeds Control Guidelines (183 KB PDF download)

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