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Please recommend a herbicide for knotweed #932642

Asked May 22, 2026, 11:45 PM EDT

Hello, my home has two knotweed plants (from a previous owner). Please recommend a chemical treatment regiment - product or active ingredients, timing (August?), etc. Thank you.

Dakota County Minnesota

Expert Response

Hi Steve, 

Thanks for reaching out. Here's a great factsheet from the MN Dept of Agriculture on knotweed and control methods: https://bugwoodcloud.org/mura/mipn/assets/File/Knotweed%20Brochure%20WEB.pdf

It is recommended to apply a foliar spray in the late summer or early fall, approximately 2 weeks before frost. There are suggested sprays on page 3 of the factsheet, along with tips for using the herbicide on page 4. 

Make sure to always follow the herbicide label directions attached to the herbicide container you are using. The site of use or plant to which the herbicide is to be applied must be listed on the label or the herbicide cannot be used. 

I hope this helps! 

An Ask Extension Expert Replied May 23, 2026, 8:04 AM EDT

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