Japanese knotweed - question and expert referrals?

We recently discovered a serious case of knotweed in whole backyard, which was unkempt for 30 years before we took over. Our contractor cut them down, and we’ve bombed the backyard with Round Up (which I hate, but necessary), and it’s worked as a short-term solution. Now that all the above-ground shoots look dead, should I dig them up and bag them and then Round Up again?

For the long-term, I want someone to actually come in and assess our issue and next steps, since the web has too much conflicting info on how to deal — anyone know of invasive species experts I can speak with?

emmajacob

in General Discussion 9 years and 8 months ago

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emmajacob | 9 years and 7 months ago

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Yes, that looks like ours before we cut it all down and started using 50% Round-Up. We’re going to start digging in Sept, but I haven’t found a landscape expert – this forum and the web have been helpful. I feel a bit at a loss. Where do you live?

laurenpacker123 | 9 years and 7 months ago

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Hi There. Im wondering if you ended up finding anyone to help you with this. I have the same thing in my yard and really need help. I see people using Roundup and doing lots of deep digging. Either way I need assistance and would love to know what you decided to do. Thanks in advance. [Yard2](//muut.com/u/brownstoner/s1/:brownstoner:icWi:yard2.jpg.jpg) [Yard1](//muut.com/u/brownstoner/s1/:brownstoner:Jlzf:yard1.jpg.jpg)

emmajacob | 9 years and 8 months ago

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Thank you so much @mh, @RedRobin, and @ESCIV!

kevrob | 9 years and 8 months ago

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I’ve been lurking on this site for years and finally posted today because I’ve been fighting Japanese knotweed in my backyard as well and it is a $@&! nightmare.

Just wanted to say, in addition to spraying roundup, in can be injected into cut stems, which I’ve had great results with. Or if you cut between the first and second node you can even pour it right into the little “cup” it makes, or brush it immediately onto the exposed “cut”. More time consuming but fewer applications overall with the bonus that you know exactly where you put it, so it won’t kill other plants.

Do this in late Aug/Sept, when the plants are naturally drawing more resources back to the rhizome and it’ll do you a favor and kill itself. Even if you excavate your whole backyard, miss an inch and you’ll be back to square one next year.

Whatever you do, buckle up. Seems like this plant fights wars, not battles. Good luck!

mh | 9 years and 8 months ago

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It is the worst. Here’s a link to an article I’d written for Brownstoner a couple of years ago:
http://www.brownstoner.com/brooklyn-life/the-dirt-all-about-weeds/
In my opinion, Japanese knotweed combines the worst qualities of ivy, mint and bamboo.

Guest User | 9 years and 8 months ago

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Helpful info for me too, mh, because we still have it where our property meets our neighbor’s. What we did when we were digging it up was put flashing in as a barrier between our yard and our neighbor’s. Knotweed is a beast.

mh | 9 years and 8 months ago

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You did the right thing by using Round Up. There is no mechanical way to get rid of it, as the roots can go as deep as 4 ft; you can’t dig it out, pull it out, or prevent it from spreading by not allowing it to go to seed, as it spreads through its rhizomes.
To eradicate it, you must be very consistent, and have the cooperation of your neighbors. You have done the first step, by killing the current growth. Now you can pull out all the dead plant material, and wait for it to grow again. Once you have 3 leaves or more, spray with Round up, let it die, and bag it. Repeat those steps all the way through November.
In the winter, it will go dormant, so when it doesn’t come back, it doesn’t mean you have won yet. Once spring is under way, and the temperatures are in the 60’s, you will see the pink shoots come out. Hopefully, fewer than this year. After about 18 months, you should have gotten rid it in your yard. If it lives in your neighbor’s yard, it will try to come back, so you have to be vigilant.
Landscape fabric doesn’t work on Japanese knotweed.
One very importan t note on Round Up: it’s popular because it’s effective and relatively safe. It’s a systemic herbicide, that works by getting to the roots through the leaves. You can’t pour on the ground, or spray the stalks. It’s also not a case of “more is better”; consistent, careful, repeated leaf applications is the only effective use of the product.
Good luck!

Guest User | 9 years and 8 months ago

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Here are some photos of what the root structure looks like. [Knotweed to e-mail](//muut.com/u/brownstoner/s1/:brownstoner:bfJI:knotweedtoemail.jpg.jpg) [Knotweed with shoe](//muut.com/u/brownstoner/s1/:brownstoner:BTjt:knotweedwithshoe.jpg.jpg)

Guest User | 9 years and 8 months ago

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I don’t know an expert, but the roots can go down 2-3 feet so they will keep growing — Round Up or not. About 1/2 are yard had it and we dug it up over the course of 2-3 summers. It was super hard work — and if a 1/2 piece of knotweed is missed, it’ll regrow — so I don’t recommend you do it yourself. Other neighbors had contractors come in and basically remove lots of dirt and haul it away — I just don’t know how much dirt you have to remove. Ultimately, we were able to win the war, though we have neighbors that still have it. What is critical is not to let it flower in the fall because then the seeds will sow again. There may not be a quick fix, particularly if it’s been growing for years. For now you should cover your yard with heavy duty landscape fabric so light won’t get to the roots.