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Question DetailsAsked on 7/15/2013

Are there any effective barriers against Japanese knotweed? Would fencing help?

My property is adjacent to conservation lands that are infested with Japanese knotweed. So eradicating the knotweed or using Roundup on it are not options. Every 7-10 days I dig shoots out of my lawn and cut back the growth, even digging out some of the root mass where it comes on my property. This is getting old, and I'm feeling like Sisyphus here. Would a fence that goes some depth into the ground help hold it at bay? I know it can grow through concrete, so I'm not going to stop it with a barrier, but I'd like to at least slow it down so that I can use the time I'm spending on it now to work on other parts of my garden! Thanks for any advice.

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6 Answers


There are barriers that are used to contain bamboo - they would probably work. However, they must be dug about 3' into the ground - major labor intensive. You're better off using a herbicide on the stuff: it's really tough to be rid of.

Answered 7 years ago by Labour of Love


Here is a fairly good article on it -

Just because your neighbor is conservation land does not mean you cannot complain to the owners about a non-native invasive plant invading your territory - who knows, they may do something about it, or give you permission to spray it.

If it is crossing your line, you have a legal right to control it, including poisoning it. I would write them a letter complaining first, and if they says they will do nothing because it is conservation land, I would then send them a letter saying you are going to control it by poisoning it on your side of the line and give them a month to take care of it or you will go ahead with ROundUp or Ranger or similar glyophosphate herbicide.

Answered 7 years ago by LCD


I agree with everything that the second poster said. Additionally, some places have regulations that require landowners (conservation or not) to eradicate invasives. Worth looking into.

Rather than digging the shoots out, get a veterinary hypodermic (because it holds a larger volume than human ones). Fill it with undiluted glyphosate (RoundUp) and inject each shoot with plus or minus 1/4 ml (cc). It takes a very small amount to kill the shoots AND it will slow regrowth from each treated shoot. Ever so much faster than digging it out: especially since even the smallest root piece left underground will resprout.

Answered 7 years ago by Labour of Love


Thanks for the all advice--the link was very helpful. At least I've been doing something useful by digging up the rhizome clumps.

Sorry if my original question wasn't clear about this--the conservation lands are not owned by an individual but by the state. The knotweed does also extend onto other neighbors' properties, so it's a pretty extensive problem. The good thing is that as the article linked above noted, the knotweed only grows at the edges of the conservation land and not at all under the tree canopy downslope from it. Maybe I should just plant more trees!

I guess my next step will be to contact the conservation commission and ask about using injectible herbicides. I'm sure they'd be happy to have some knotweed eradicated but they may not want the herbicide introduced in the first place. Next spring after the snow melts but before the stuff starts growing I'll also try the tarps. And you never know, maybe I could trigger the state to want to start some kind of eradication program, as is done with purple loosestrife :-)

Answered 7 years ago by Guest_9700337


There is nothing that your state can do about you killing Japanese knoweed on your property - unless you use a banned chemical. Truly, you are spreading it more by digging it than other methods of killing it. Tarps will slow it down but it will always be making more root runner to spread by. Injecting it with gly. will only kill the root of that one stem back a foot or so. It will not travel onto the conservation lands.

Answered 7 years ago by Labour of Love


Look for state eradication programs that might exit in your state by googling this phrase -
state programs to eradicate Japanese knotweed

If there is a state eradication program, then they will HAVE to attack the problem, and you may also have cause to send them an abatement notice that will require them to eradicate the problem - of course, call the responsible office and talk to them first - no need to stir the bureaucratic hornet's nest unecessarily.

Just as an FYI to those reading this article - one observation on the comment about the state not being able to do anything about eradication steps you take on your land. From a legal standpoint, that is not strictly true. While you can cut overhanging or invasive vegetation encroaching on your land from a neighbors, if what you do kills the plant or causes it to fall on the neighbor's land (say cutting half the branches and all the roots on your side of a neighbor's tree near the fenceline, killing it or causing it to fall into the neighbor's yard), then you can be held liable for the damages unless you have formally sent an abatement request to him and allowed reasonable time for him to correct the issue his own way.

The same is true of other infringements too - you cannot just cut or burnn down a shed built partly onyour land without gibving the neighbor the opportunity to remedy the trespass, or block and dam infringing concentrated runoff that he has created without giving him the opportunity to diert it away from your yard.

Injection of glyophosphate into roots or spraying the plant on your side would not cause this sort of a problem with an invasive plant like knotweed or bamboo (knotweed is also known as japanese bamboo) as it might with an overhanging tree, for instance.

Answered 7 years ago by LCD

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