Knowledgebase
Japanese Knotweed #746535
Asked April 27, 2021, 11:37 AM EDT
Hennepin County Minnesota
Expert Response
Unfortunately, if you're neighbor isn't going to eradicate the knotweeds, you will keep having them pop up in your yard. If you have a sharp spade I would periodically go along the edge of your fence to break any runners that the parent plant has sent under the fence.
In your yard, I would recommend hand removal combined with an herbicide that includes glyphosate (the active ingredient in RoundUp). There are good instructions here: https://blog-yard-garden-news.extension.umn.edu/2018/06/aggressive-weed-challenges-mn-gardeners.html
If you are comfortable with it I would talk to your neighbor about removing the plants, knotweed is on the DNR's control noxious plant list and your neighbor is responsible for keeping it from spreading onto your property. You can share this page from the DNR on knotweed with them: https://www.mda.state.mn.us/plants/pestmanagement/weedcontrol/noxiouslist/knotweed