Thanks for your question.

As coincidence would have it, I have just returned from my own gardens in dealing with this weed. It is a tough customer. I believe that this plant is Horseweed (Erigeron canadensis). It is not easily eradicated. It is an annual plant capable of wide seed dispersal in late summer. Your best hope of dealing with it is to pull it all up, especially before it fully blooms.  I fully appreciate the fact that this is a very labor-intensive way of eliminating it.

There are very few herbicides that are effective against it. Herbicides like atrazine, metolachlor, or simazine have some effect in preventing seedling establishment before the weed emerges. Dicamba, or 2,4-D, is commonly used for post-emergence control. Resistance to glyphosate has been reported, so using a combination of herbicides or herbicides with different modes of action may be necessary. However you will need to do this for a few years before you can eliminate it. Their seeds can remain dormant in the soil for several years.

See the following for further information including control procedures:

http://www.minnesotaseasons.com/Plants/Canadian_horseweed.html

https://davesgarden.com/guides/articles/horseweed-erigeron-canadensis-useful-plant-or-noxious-weed

https://www.wildflower.org/plants/result.php?id_plant=coca5

https://www.mda.state.mn.us/pesticide-fertilizer/dicamba-general-information - :~:text=In 2016, Minnesota registered three new dicamba,dicamba was registered for pre-plant and pre-

https://www.extension.purdue.edu/extmedia/gwc/gwc-9-w.pdf

Good Luck!

Thanks for your response.

Look on the bright side of things. This is an annual plant so as September approaches, it will start to die off. The most critical thing to do is to prevent it from going to seed. It should pull up easily. Maybe the quickest way of attack is going in with a weed-wacker and cut things down. Don’t worry about the roots as they will die. Cut down all the flower stalks, rake them up, and throw them into the trash in garbage bags. If you assiduously do this for the next three years or so, you should make a dent in their population. Also consider applying a pre-emergent herbicide next Spring (early April 2025).  As I mentioned before, an herbicide containing atrazine, metolachlor, or simazine should be reasonably effective. Be sure that the product label on the herbicide indicates that it is effective against horseweed.

Good luck. Have fun. Get back to us with any further, related questions.

Glad to be of assistance.  Thanks for consulting our forum.