Canadian Thistle

It has been a busy few weeks for me — holiday traveling, Green Expo talks (that’s our regional conference), and getting ready for a semester leave this year — I’ll be working on a project investigating how professors transfer information to the public.  But during this time I have, for some unexplainable reason, been thinking about Canadian Thistle.  And do you know what I’ve come up with?  This: 

It’s a colossal waste of time and money to worry about Canadian thistle. 

Despite its name Canadian thistle is not native to North America.  It was introduced in the 1600s — probably by accident.  Most parts of the plant are edible and some people even say that it’s tasty.   Though it can be found across the US it is rarely found in such high concentrations that it displaces native species.  Where it does dominate the landscape conditions are usually bad enough (highly disturbed sites) that other plants won’t fare well anyway.  Canadian thistle is known as an early succession plant which means that it will establish in a disturbed site — perhaps even taking it over — but will slowly, over years, be taken over by other plants.

Canadian thistle is considered a noxious weed across the United States, but it is classified that way mostly because of political pressure rather that for what it does (if nothing else it is a very visible, nasty looking plant).  People may get scratched up, but you won’t hear about anyone dying from Canadian thistle poisoning.  As an agricultural weed it can be significant, but usually pales in comparison to other weeds.  Because it is listed as a noxious weed some states and local governments have tried to rein it in, at least over small areas, but this thistle is very resistant to herbicides, and tough to kill just by pulling, and so efforts are often fruitless. 

Should we redouble our efforts and assail this thistle with more energy?  I just can’t bring myself to say yes.  This weed may be undesirable, but to put much money into a losing battle with a weed that has been here for about 400 years and that mostly affects disturbed sites seems like a silly strategy.  In my mind we should be treating this weed as undesirable, but not nearly at the same level as other invasive or noxious plants.</d

17 thoughts on “Canadian Thistle”

  1. Jeff,
    I agree a war on Canada thistle will be about as successful as our war on drugs. But, damn, that stuff is nasty in pasture!

  2. You obviously don’t live near horse people, Dr. Gillman. They’ll have the noxious weed police after anyone who takes that attitude.

  3. Using toxic chemicals to kill plants, regardless of how undersirable they are, has always seemed wrong to me. No herbicides in my yard. Weeds are stopped by mulch or pulled by hand.

  4. If you pull this weed by hand, be sure to have on some extra heavy duty leather gloves. It’s about as prickly as plants (besides cacti) get. I remember stepping on one of the evil things years ago while barefootin’ in our yard. Not pleasant!

  5. Why do horse people hate it? Is it a nuisance on the riding trails or is it somehow unhealthful for horses?

    Are their greens part of the edible part? I might find a place for it in my vegetable garden- somewhere between my perennial arugula and mint.

    It is one of the more annoying weeds in my nursery.

    I vote for ending the war on drugs and Canadian Thistle.January 08, 2012
    by
    Ray EckhartHorse people hate it because horses won’t eat it, and, as Dr. Cregg alluded to, left unmanaged, would take over pastureland. I understand that goats will eat it, though.January 08, 2012
    by
    Julie Hollingsworth HoggWell, I think it’s pretty.January 10, 2012
    by
    Alan HaighRay, I can’t see where it was alluded to in the article after having just reread it. He states that it is primarily a problem in recently disturbed soil which is not generally the conditions of a pasture. Does it take over pastures because the grazers eat around it giving it an advantage? It certainly doesn’t take over the undisturbed meadow on my property where browsing is done mostly by deer. It only settles in areas that have recently been cultivated. January 10, 2012
    by
    Ray EckhartI’m not a horse person, nor do I know a whole lot about pasture management. However, the horse people I know hate the stuff and do their best to keep it out of their pastures, and, since it’s on the PA noxious weed list (because of horse interests? – dunno), do their best to make sure others do their best to manage it elsewhere. This is also true for the other thistles on the PA list – Bull thistle and musk or nodding thistle. BTW, Ag interests account for 7 of the 13 species on the the PA list – the three thistles, goatsrue, shattercane, jimsonweed, and Johnson grass. Environmental interests account for 4 (Purple loosestrife, Multiflora Rose, Mile-A-Minute and Kudzu), 1 is purely political (Cannabis sativa) and 1 for general welfare harm to people (Giant hogweed).January 10, 2012
    by
    Ray EckhartThe allusion I referenced was in the first comment by Dr. Cregg: “…But, damn, that stuff is nasty in pasture!”January 10, 2012
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    Which is why I was asking what was nasty about it. Thanks for answering me though. I’m still curious to hear from someone who can give me a complete explanation. Here I’ve never seen it dominate a meadow. January 10, 2012
    by
    Ray EckhartHere’s a 48 page pdf of horse pasture management, published by the University of Minnesota, found by a simple google search. Perhaps Dr. Gillman could ask his colleagues referenced in the document to answer any additional questions you might have.

    http://www.extension.umn.edu/distribution/livestocksystems/DI8646.pdf

    January 10, 2012
    by
    Jeff GillmanRay, for some reason that link shuts down my computer — but I think it’s my computers fault. Anyway, horses and thistles. First, I was brought up in PA and my first job was caring for horses. My parents always kept horses and my parents still keep a couple on their land. Both my mother and sister used to show. That said, I really can’t stand horses — not at all. Anyway, Canadian Thistle isn’t bad for them and I know that many horses actually like them. For those that don’t I suppose that a major infestation could be quite a pain — it would certainly be tough to move around in a dense field of them. But I wouldn’t expect major problems beyond some pricks. Since I can’t see that article let me know what they’re saying the major problems are and I’ll be glad to see what I can find.January 10, 2012
    by
    Ray EckhartResponse to Jeff via email. Copied below:

    Here’s the google search I did:

    “Canada Thistle” horse pasture site:*.edu

    It’s the first item that comes up.

    It won’t let me copy/paste from the document, though. Authors are:

    Krishona Martinson, Roger Becker, Lynn Hovda, Mike Murphy.

    Reviewed by:

    Ron Genrick and Jochum Wiersma

    Contributing authors are Beverly Durgan and Paul Peterson.

    Funded by the Minnesota Racing Commission. Copyrighted 2009 by the U.(which probably explains the copy/paste restriction) but available from shop.extension.umn.edu Publication number 08646January 11, 2012
    by
    Alan HaighRay, if you read it please give us a brief summary. No need for us all to do an individual search. January 12, 2012
    by
    Jeff GillmanBasically all I can see is that horse people consider Canadian thistle a noxious weed, but I don’t see a lot of specific reasons — so I’m not convinced.

  6. Horse people hate it because horses won’t eat it, and, as Dr. Cregg alluded to, left unmanaged, would take over pastureland. I understand that goats will eat it, though.

  7. Ray, I can’t see where it was alluded to in the article after having just reread it. He states that it is primarily a problem in recently disturbed soil which is not generally the conditions of a pasture. Does it take over pastures because the grazers eat around it giving it an advantage? It certainly doesn’t take over the undisturbed meadow on my property where browsing is done mostly by deer. It only settles in areas that have recently been cultivated.

  8. I’m not a horse person, nor do I know a whole lot about pasture management. However, the horse people I know hate the stuff and do their best to keep it out of their pastures, and, since it’s on the PA noxious weed list (because of horse interests? – dunno), do their best to make sure others do their best to manage it elsewhere. This is also true for the other thistles on the PA list – Bull thistle and musk or nodding thistle. BTW, Ag interests account for 7 of the 13 species on the the PA list – the three thistles, goatsrue, shattercane, jimsonweed, and Johnson grass. Environmental interests account for 4 (Purple loosestrife, Multiflora Rose, Mile-A-Minute and Kudzu), 1 is purely political (Cannabis sativa) and 1 for general welfare harm to people (Giant hogweed).

  9. Which is why I was asking what was nasty about it. Thanks for answering me though. I’m still curious to hear from someone who can give me a complete explanation. Here I’ve never seen it dominate a meadow.

  10. Ray, for some reason that link shuts down my computer — but I think it’s my computers fault. Anyway, horses and thistles. First, I was brought up in PA and my first job was caring for horses. My parents always kept horses and my parents still keep a couple on their land. Both my mother and sister used to show. That said, I really can’t stand horses — not at all. Anyway, Canadian Thistle isn’t bad for them and I know that many horses actually like them. For those that don’t I suppose that a major infestation could be quite a pain — it would certainly be tough to move around in a dense field of them. But I wouldn’t expect major problems beyond some pricks. Since I can’t see that article let me know what they’re saying the major problems are and I’ll be glad to see what I can find.

  11. Response to Jeff via email. Copied below:

    Here’s the google search I did:

    “Canada Thistle” horse pasture site:*.edu

    It’s the first item that comes up.

    It won’t let me copy/paste from the document, though. Authors are:

    Krishona Martinson, Roger Becker, Lynn Hovda, Mike Murphy.

    Reviewed by:

    Ron Genrick and Jochum Wiersma

    Contributing authors are Beverly Durgan and Paul Peterson.

    Funded by the Minnesota Racing Commission. Copyrighted 2009 by the U.(which probably explains the copy/paste restriction) but available from shop.extension.umn.edu Publication number 08646

  12. Basically all I can see is that horse people consider Canadian thistle a noxious weed, but I don’t see a lot of specific reasons — so I’m not convinced.

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