Musk Thistle Eradication #447452 - Ask Extension


Musk Thistle Eradication #447452

Asked April 12, 2018, 2:38 PM EDT

We live in Big horns and last year had a large Musk Thistle out break. I walked over 40 acres and cut these thistles off at their base and sprayed "red" round-up into the stalk(s). I cut thistles down prior to their head flowering. Is this effective control? Are the  seed heads, though they had not flowered, still able to regenerate. Do you have any suggestions at the most effective elimination methods.  We had horrible out break.

Johnson County Wyoming

Expert Response

The first thing to do is to ensure that the species is truly musk thistle. Montana has a very good guide ( to do this.  Identification is important because Musk thistle is a biennial which has implications for control measures. Effective muck thistle control can be achieved through many chemical options; however, more importantly is finding an option that does not injure the desirable vegetation.  I am not certain what "red" roundup is but roundup is effective but also non-selective so the herbicide must be very carefully applied to not injure other vegetation.  A more selective option would be aminopyralid (Milestone).  Nonetheless, when trying to manage musk thistle, the most important element is the seedbank.  As you mention, ensuring seed production does not occur is most important because the species depends on seed to produce (unlike Canada thistle).  We do not have a good sense of seedbank longevity of musk thistle but you can expect to see the population of musk thistle to persist for many years, albeit declining.  Last year was a wet spring for most of the state; this can make the outbreak worse for species such as muck thistle.  Be persistent and selective with your control and you will eventually see the benefits.
Daniel Tekiela Replied April 13, 2018, 12:45 PM EDT
Hi Daniel,

Thanks for your response. Yes, our area had a large Musk & Canadian Thistle outbreak last year. For the Musk Thistle's, I walked 40 acres with hedge shear and cut the stalks off about 4" above the ground then sprayed round-up down each stalk. I cut these down when the thistle head had formed but had yet to open. A walk around the same areas over the past couple days showed essentially no signs of re-propagation. The Canadian Thistles were just too thick to attack the same way. At least on my property, I attempted to cut the heads off prior to flowering and was probably 85% effective. 

My question to you is: what treatment do you suggest for the Canadian Thistle in an attempt to eradicate or at least minimize? The Musk is fairly easy to deal with, I walk around with a spray (stream) bottle of round-up and hit the ground rosette. 

I would appreciate any comments/advice you may have.

The Question Asker Replied May 21, 2018, 8:30 AM EDT
Because Canada thistle is a creeping perennial the "root" of the issue is the roots.  Thus, it would take many years of aggressive above ground management to really make any long-term headway.  Alternatively, a very successful product that many of our professional managers use is aminopyralid or Milestone as it is known in the trade. It is fairly selective towards broadleaf plants making it ideal in rangeland situations and it moves down into the root system and controls both above- and below-ground vegetation. However, it can still damage desirable vegetation so being selective as possible is preferred.  It sounds like you may have monoculture patches where you aren't too concerned about other species so hopefully this is not too difficult a task. As always, if you intend to use this product ensure that you meet the requirements of the label.
Daniel Tekiela Replied May 23, 2018, 10:49 AM EDT

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