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Invasive Thistles #926035

Asked March 14, 2026, 5:36 PM EDT

Hi! I’m in Strasburg and have a patch of Canadian thistles on my property. I know these are an invasive species and they are already crowding out beneficial native plants even with keeping them mowed down. What can I do to eradicate these permanently? I don’t love the idea of using systemic herbicide, but if a one time application will do it I may just have to embrace it.

Arapahoe County Colorado

Expert Response

Hi Kendra,

Thanks for reaching out to Ask Extension with your Canada Thistle questions.

Here is our CSU resource for Canada Thistle:

https://extension.colostate.edu/resource/canada-thistle/

Here is the CO Dept of Ag info on Canada Thistle:

https://drive.google.com/file/d/1VD0akK6512uYeraw77xI7XVKujmUh81u/view?pli=1

Both publications above list the mechanical, cultural, biological, and chemical control methods for this noxious weed.

I hope this helps,

Dawn 

Dawn Fradkin Replied March 16, 2026, 11:12 AM EDT

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