Killing Canadian Thistle
I have a lot of what seems to be Canadian Thistle. I am unsure because some of the stems are spiny, rather than smooth. See photos. Also, it does not necessarily grow in clumps. The partly-opened lavender-colored flowers are 1/2 inch across now, near the end of June. The infestation took hold long ago, on sunny ground below a pine and a spruce tree. It has extended well into my yard which is grass and other plants. I followed my city's recommendation to pull the plants and put thick newspaper down below surface level. I find now, through experience and reading, that this is far from the correct approach. I hesitate greatly to buy the array of chemicals recommended, and to apply the ones that require (to my knowledge) expert handling. Your advice would be much appreciated.
Hennepin County Minnesota
Canada thistle usually does not have spines along the stem. However, all the other non-native thistles do, and the native ones do not. So you should try to get rid of it. Check this link:
Repeated pulling will eventually weaken the plants. Don't let it go to seed. Spot treatment with glyphosate (Roundup), but you may have to repeat. Glyphosate is non-selective, so it will kill anything green that it touches. Read here:
I had attached photos to show you that some of the stems were smooth and others had spikes. Also, I asked about how to apply the array of chemicals that other websites (USDA and Colorado State U) advise, They recommend Roundup BEFORE blooming time. Is there a company that can be hired to deal with this?
Lawn care companies are licensed to use herbicide products homeowners can't use. If you are looking for a company to do this job, that would be where I would start.
Herbicides work best when temperatures are moderate (60-80). Also, herbicides work best when the plant is actively moving energy from the plant to the roots. But Canada thistle is a tough plant, so herbicides both in the spring and fall may be necessary. There are various protocols and herbicides. Read here for another take on this from Purdue:
Thank you very much!