Japanese Knotweed!

Asked June 1, 2018, 3:11 PM EDT

I have this in my yard in NE Mpls. It’s been here, most likely, since before I moved in. I had it looked at about 10 years ago, and that person said it was NOT knotweed. However, it is taller than it’s ever been now, about 20 shoots, and it is definitely knotweed. I have read online info about using a specific herbicide to treat the cut stems, twice per year. Forever. I understand this, but would be really much more comfortable if someone could look at the location here, and walk me through the first treatment, and confirm my understanding of the correct timing of the treatments. I have left a phone message today with the MN Landscape Arboretum, but that message says I will get a reply within 4 days. I have a message elsewhere that is not being returned. I am really hoping for some support with this before my neighbor and I both have a tall stand in the middle of our trees and bushes! Thank you very much in advance for your reply. Diana

Hennepin County Minnesota

6 Responses

I am sorry this forum is for web questions only. It is staffed by volunteers in MN and none make house calls. The Arboretum answers phone questions but staff do not make home visits. Japanese knotweed can be eradicated. One must be more stubborn than the weed and very persistent. One treatment is to cut off the stems at about 1 ft above the soil and treat the remaining leaves and stems with roundup or glyphosate. Wait about a week or until the stems look dead then dig up all the roots. Dig down about 1 ft with a fork and break apart the soil and collect the roots. Repeat each time any knotweed comes up. There are seeds in the ground so this effort will take about 3 years. Every year will be less work. It can be done and should be, the plant is very aggressive and harms natural areas. https://www.dnr.state.mn.us/invasives/terrestrialplants/herbaceous/japaneseknotweed.html

Thank you for your prompt reply! I will certainly do my best. I’m not going to let it take over the world from my yard.

It is a tough one but my neighbor got rid of a 10 year old plot of the stuff without chemicals, He just kept digging it out. Killing it will make the roots easier to remove. Good luck.

Interesting! Everything I’ve read said that won’t work. I have someone coming to consult who will use pesticides - which makes me sick at heart. I will talk with him about digging. Not a good site - on a slope between two properties.... But very good to know that it might be possible. Thank you again!

In general it does not work because the average homeowner does not keep up the effort for several years. Targeted herbicide applications are beneficial and are a responsible thing to do. Getting rid of a very invasive weed will in the end mean much less herbicide use because the area of infestation is small at this time. Other homeowners may not have the knowledge you have to use effective treatments.

Thank you again. Yes, I will ask the person coming over (hopefully soon!) who works in native landscaping what his best idea is. We might try digging first, but will definitely do the herbicides if that’s the best guess at what will help. I’m so antsy to get at this. It is growing so fast this year. Thanks.