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Canada thistle

Posted by fredbarber z4 CO & z6 MA (My Page) on
Wed, Sep 1, 10 at 10:49

I'm a part time Northern Colorado resident fighting an ongoing battle with Canada thistle and musk thistle. Based on my usual schedule of visits, I've settled on a regimen of mechanical control (cutting down everything I can in the summertime) and chemical control (spraying in the fall).

For some number of years, I've been using Curtail with limited success. My big jug of concentrate is now empty, so I've revisited online recommendations before buying more.

It seems like the top rated stuff available to consumers is now Milestone.

Does anyone on this list have experience with Milestone? Alternate recommendations? Sources in Northern Colorado (Front Range communities from, say, Denver to the Wyoming border)?

Thanks in advance,

Follow-Up Postings:

RE: Canada thistle

We only have Russian Thistle so we can just pull it and be done with it. But, I used to work in a nursery and we sold Roundup for Canadian Thistle. It's salt-based so is considered less toxic than most herbicides. That's all I got. Good luck!

RE: Canada thistle

Don't need Roundup - just use a generic. Glystar is very cheap, but you will need to add a good surfactant for thistle. If it's in rangeland, or you want something else specific for broadleaf, go for turflon ester or anything with triclopyr. Actually for rangeland etc, the label on Remedy Ultra should allow you to use it, and it is considerably cheaper and almost exactly the same. Spray it when temperatures are below 70 and you will toast the thistle. It may never come back if you get good coverage. Triclopyr is that good on thistle! Don't skimp on the surfactant though.

RE: Canada thistle


I know this is almost a year later - but I have just been dealing with this myself, and have done some research which I hope I will explain correctly.

The plant tends to spread by root system, but also seed if it lands in a moist environment that has recently been disturbed (road building, cultivation). If it is allowed to reach the second year, the root system can become very extensive.

It turns out that treatment times are very important in controlling Canadian Thistle. The best time to cut it down is late spring when the flowers are just created. This is because the energy stored in the root system has been somewhat depleted. You can also mow or chop down repeatedly through the growing season. The best time to use herbicide (and I frequently saw Roundup/glyphosate recommended) is during an active growth period (usually when there is a lot of moisture) so that the herbicide will be transmitted down to the roots (while the plant is photosynthesizing and sending the energy down to that root system).

The real bummer is that the seeds can germinate up to 20 years after they have been released. But Canadian Thistle is not very competitive with a lot of plants, so when you disturb soil, you want to get something else in there ASAP and stay on top of any thistle that germinates. In the first year, the thistle is just a rosette, the second year it reproduces by sending up a stalk and flowers/seeds and creating the extensive root system. So it is best to get to it when it is that low-growing rosette (almost like a dandelion).

If you harvest by pulling up (or maybe even cutting down) during a period of active growth, this can actually stimulate the roots to produce many more plants! So you want to be careful to do this at the right time, and watch for recurrence.

Hope this is helpful for someone.

RE: Canada thistle

I had a happy accident with this stuff. I was just to lazy, er uh, busy to get the salt block out to the pasture. Sat in front of the barn for a few weeks. When I picked it up and moved it out back, the thistle that was there, was no more. 50lbs red salt/mineral block $4.59 could probably use it this way a few hundred times.

Probably not where you want to plant anytime soon, but cannot be any worse that Roundup and all the other junk.


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