Idaho Weed Awareness Campaign
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Scotch Thistle

The Enemy - Onopordum acanthium (Scotch thistle) is a flowering plant in the Family Asteraceae. Other common names include cotton thistle, and Scotch cotton thistle. Native to Europe, North Africa and Asia, it is a vigorous, biennial with coarse, spiny leaves and conspicuous spiny-winged stems.

Scotch thistle represents a serious problem. Number one, it is unpleasant and can be found along bikepaths, trails and other recreational grounds. You also often find it in pastures and along waterways, such as the Boise River. This weed is quite a prolific seed producer. The rosette, if left untreated by the end of the season, will easily be wider across than he can reach with both arms. By this time the plant will build a big fleshy taproot and go into senescence. The next year the bottom leaves go flat and it will bolt and grow eight to ten feet tall.

The Defense - One possible way to eradicate Scotch Thistle weed is to dig it up, making sure that you cut out the root crown. Start digging a couple of inches away from the plant. After digging a few places, use the shovel to cut the plant near the bottom and then remove the root stalk.

Spraying a giant, second year plant is somewhat ineffective - it is best to spray the rosette in the spring, even though October, with a broadleaf herbicide.

DOW LogoMilestone at 5- 7 oz product/A when plants are in the rosette to bolting stage or on fall rosettes.

Link to Milestone label.

Click for general recommendations on Dow AgroSciences Herbicides.

For technical information on use of Dow AgroSciences herbicides to control of invasive noxious weeds click here.

Click here for more technical information on use of Dow AgroSciences herbicides to control of invasive noxious weeds.


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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