9 Common Mistakes To Avoid in Trying to Control Invasive Knotweed

[@wikipediaboo]

Thank you for this concise and well researched video! I discovered we had a small batch of knotweed by the side of our house and went into an internet rabbit hole of doom. This video made it clear what needs to be done and the persistence it takes to eradicate this Darwin winner. I both admire it and fear it.

[@GreenShoots]

You are welcome! It really is an amazing plant, and I agree that it deserves respect. It's our mistake that we brought it to the wrong places in the world.

[@SuperFeist]

This is one of the most comprehensive and well informed videos on knotweed treatment on this platform, thanks for uploading! My quite large patch of knotweed just received its first foliar spraying treatment, after it was very hard for me to just leave it alone for all of summer. I set up a camera to do time lapse videos of the herbizide effect and regrowth next season. What I was asking myself: Soon, the upper parts of the plant will have died of. The rhizome is probably not yet in full dormancy (mid october), but already weakend by the herbicide treatment. Would it make sense to carefully dig free some of the bigger sections of the rhizome and drill vertical holes right into it to fill them with concentrated glyphosate? Idea is that it is translocated all through the not yet dormant rhizome? Anybody ever tried that?

[@GreenShoots]

Thank you for that comment, @SuperFeist! What you propose would seem to make perfect sense. However, I don't believe it would help you out. I say this for two reasons: First, I have not found applications of herbicide directly to the rhizome vascular tissue to be that effective. I am not sure why. I tried something similar fairly recently, and it didn't work: Kill Invasive Japanese Knotweed with Herbicide in Late Fall or Winter when It’s Dormant: kzbin.info/www/bejne/b4qQYZt6f9-DkM0 . Second, I don't like to excavate in a patch treated in the fall until a little bit later in the spring. Why? Even in early spring, it seems the herbicide applied in the fall is still moving within the rhizome and crowns. For example, I have seen small sprouts from winter buds on a fall-treated knotweed cluster start to grow in the early spring. (Initially, I thought that treatment was unsuccessful.) Then, a couple weeks later the sprouts withered, and no other sprouts appeared within about a 4 foot radius of that treated crown. My thought is that the herbicide was still moving in the rhizome. But knotweed is still pretty mysterious. Maybe give it a shot on part of your patch?? And, consider posting that time-lapse video!

[@SuperFeist]

​@@GreenShoots very helpful, thanks for the reply. I wasn't aware of the possibility that herbicide might still be moving within the rhizome for several months after application. I'll better be patient now until spring then - knotweed requires too much patience most of the year for my taste. But in spring, when distribution of fall herbicide treatment is complete, I will give it a try with drilling into the rhizome and pouring glyphosate in. Will post the time-lapse video from my fall treatment in few weeks, recording is still ongoing. Regards from Germany!

[@GreenShoots]

@@SuperFeist - one critical point I should mention: the example I gave was from a site treated in a northern state, Minnesota, where the ground freezes in winter. Your results in Germany could be different. You might look at the research paper by Price et al. 2002. They used carbon 14 to track carbon movement in the rhizome of knotweed in the UK. Tschüss!

[@FireEaterJahfre]

We're into our 4th year of Japanese knotweed eradication; we started the year we bought this place. No herbicides were used. My wife played the role of excavator. Bless her heart, she dug more than I could have imagined at the beginning. We knew it was not going to end the stuff but we decided to get as many rhizomes as possible. Our Knotweed was in a section where filled land transitioned about 8' down to the natural ground level. The patch is shaded well so not much else grows back there. It is 140' long and 30' wide. The fill work was done in the 1970's. I don't know if the knotweed started then or sometime later. Year 2 we finished the excavation including a trench all around it to establish a boundary. We double tarped the trench and backfilled to level. Then the entire area was tarped. We taped all of the seams. All told we had two pickup loads of rhizomes and crowns. We bagged and sent them to the landfill. Year 3: The knotweed has now had almost no sunshine for 2 years. We rolled back the tarps and found the most vital remaining rhizomes and dug them out....replaced the tarps and remained vigilant, digging out any new sprouts around the area. We've only found a handful...but just ONE is too many. This was year 4: We rolled the tarp ack and found very little regrowth after 3 years with no sunlight. We covered the entire area with another very heavy duty tarp. Next year is year 5 and we'll be adding a layer of bark mulch. We didn't want to do that in case we had to back-track....because this stuff is unbelievably resilient. We only found two stray sprouts this year...feeling pretty good about it so far.

[@GreenShoots]

That's an amazing effort. Congratulations on nearly eradicating it!

[@Aspetta11]

Thank you for sharing this!

[@deBiezel]

This is the best video that I have seen on this subject. Thanks!

[@GreenShoots]

You are welcome! Thanks for your support.

[@MaxineStuart-ss1kc]

I love you. I’ve made many of these mistakes in my years-long battle with knotweed along my house, but I’m not giving up yet! The challenge now will be letting it grow until fall when I hate its guts so bad.

[@GreenShoots]

Why thank you! One other option if your treatments in the past have been successful is doing excavation of the straggler knotweed stems. We just posted a video on that kzbin.info/www/bejne/oWi6mHqIntSXf8Usi=3a4I8OjMRemfYc3O Good luck!

[@karmasong74]

I hate watching mine grow to. It's hideous!

[@GreenShoots]

@@karmasong74 That's probably the biggest difficulty people have - waiting for the right time to treat the knotweed.

[@Hbernhardt22]

Great information. I’ve been battling my JKW for over 20 years. All of my recent research aligns with your video so I am ready to attack it correctly this year!

[@GreenShoots]

Thank you for that comment! I hope you have success. What are some key things you learned from that 20 year battle?

[@afriendlyhorse]

Excellent video and explanations. Confirms research that I've seen in gardening groups about the best way to tackle knotweed. Since it's a plant that evolved in volcanic conditions, its ability to recover when almost completely destroyed is quite impressive. I wish states had better official procedures, I've felt physical pain the times I've watched a mower mowing the edge of highways contaminated by knotweed, knowing that it's only going to spread... Same thing with people covering, the underground network of the plant is much larger than you'd expect and it will spend all of it's energy till it finds the edge of the covering, and then it will pop up and continue happily.

[@GreenShoots]

Exactly, Maria! Mowing knotweed is almost like using a seed spreader. Mower decks gather the knotweed stem fragments and then fling them into new areas thus extending the infestation. I feel that physical pain too! I also think you are right to compare covering to the conditions faced by knotweed in its native area. Covering may be similar to the ash that occasionally covered knotweed infestations in Japan.

[@Thee-_-Outlier]

What is also interesting is that it's very high in resveratrol, which has disease and inflammatory damage recovery properties in humans. It's even considered to be a potential key to anti aging research by those in that field

[@katkameo6413]

Great video! Concise and to the point. I just moved into a property that was hugely neglected and I have two stands of knotweed! Never heard of it till now. This video helped so much, I was cutting them down and planned on mowing. What an ugly plant ..just why...

[@GreenShoots]

Thank you so much! Very glad to hear it helped you.

[@kevinholmes8147]

Great video! Covered everything one might need to know about the process. I have tried everything except herbicide at this point. 2 years into attempting to clear a 3/4 acre of knotweed in my yard. Started with making paths through, then removing dead shoots, then burned them. Starting to make progress with digging up clusters. Will try herbicide treatments this fall. Hoping to be able to get some use out of my yard one day!

[@GreenShoots]

You should be able to use your yard soon. The combination of herbicide treatments in the fall and digging in spring and early summer is very effective. Good luck!

[@TheDizastarmaster]

Excellent information. I have had a lot of success treating small patches using stem injections but if it returns I will try treating it later in the year. Thanks

[@GreenShoots]

Thank you for the support!

[@danielwylie-eggert2041]

Incredible information. Thank you so much for putting this together.

[@GreenShoots]

You are most welcome! Thank you for the support!

[@58DELLA]

Great video, I had a large stand of knotweed, sprayed it twice every year starting late summer/early fall (with 4oz of 41% glysophate mixed with 1 gallon of water). Killed 80% the first year, most of the rest the second year. this spring I found three little plants, they will be sprayed in the fall. Green shoots is correct, follow his advice. P.S. Don't mow it, don't cut it, you'll spread it all over the yard!. Kill it first.

[@GreenShoots]

Thank you, Perry!

[@juiceman23]

Yup I made that mistake.

[@katie4408]

You have given me some hope! Thank you.

[@GreenShoots]

Good luck!

[@Chain987]

I have this thing about 6m2 at my property in Ontario and just found out what this nuts thing is. I Dug it out this weekend hard with pick and followed the roots going and what I found interesting, it nested below concrete stairs fundaments.I am south Europen and this thing have the Same rooting as a fig tree.Exactly the same but way more invasive. They like wet concrete or stone deep underneath. Wet and safe from anything. It is impossible to kill it without removing the base of the concrete where the root Is hiding. Luckily I bough this property after fire destroyed and that fundaments will be gone. Just my experience. I will treat with herbicide in the fall and keep you posted. All the dug out roots I will burn in the metal barrel, bit by bit. What a crazy plant.

[@GreenShoots]

Very interesting description! Thank you for adding it. I have great respect for invasive knotweed. It "knows" how to survive in adverse conditions. I assume it was taught these survival skills in its native volcanic habitat in Japan and other parts of Asia.

[@dereksantavenere2172]

i have been using your product - this will be my second year i actually had good luck with cutting new pop up shoots and putting your product on the cut stem - i would also dispose of the cut portion-the return rate was slowing down with each treatment and in less quantity. i did this before mowing to prevent an accidental spread as untreated cuts would result in more new pop up shoots .i ended the season by allowing a bit more growth before fall treatment -

[@GreenShoots]

Derek - That's great to hear! It sounds like you have knotweed coming up in your yard. One thing you point out that is critical - treating every stem. So, you are cutting them and treating them before you mow? Would you cut the stems low enough so that the mower wouldn't hack of the recently treated stem?

[@dereksantavenere2172]

@@GreenShoots yes i cut it shorter than i mow. i separate the grass and cut the stem approximately 3/4 of an inch then appy a small amount of your product just on the fresh cut stalks- this allows almost no grass being killed - any pieces are dried and discarded. i mostly bag my clippings- this helps not spread any unwanted glyphosate and leaves a little blue stem sticking up so i can monitor and address any new sprouts

[@GreenShoots]

@@dereksantavenere2172 Ah! that's a very handy way to do it!

[@Vibecomp]

This has been really helpful. So how do you deal with it during spring and summer? Just let it grow until fall?

[@GreenShoots]

Great to hear! Yes, just let the knotweed grow during spring and summer. The only thing I suggest people do - if they want to get at the knotweed - is to dig or excavate knotweed crowns, starting on the periphery of the patch. The key with that is carefully disposing of the excavated crowns to make sure the crowns don't re-sprout on your property or somewhere else.

[@mysterycrimecult9340]

@@GreenShoots Thank you for the video. I'm commenting here because I have concern about a few stalks that are growing in a visible area. You mentioned bending knotweed to make a path...could I bend the visible pieces to kind of hide it so it can keep growing until treatment? Won't it snap, and will that have the same effect as cutting? It's in a trimmed hedge and 3 stalks stick out. A neighbor may come and chop it. So far I'm lucky and have "only" about 20 stems--no big stands-- so I want to let them grow and hit them hard in the fall. Thankyou, signed "The Overthinker"

[@Robc509]

Thanks for these videos. We’ve bought a house with a large garden and it have quite a large infestation that I will take care of this year

[@GreenShoots]

You are welcome! Good luck on the task ahead.

[@videovoer8130]

Thanks for this video! It shows that knotweed is easy to get rid of as long as you know what to do. Let's hope that people and governments use these steps to get rid of the plant

[@GreenShoots]

You are welcome! I get so many calls from homeowners why have just moved into new houses and discovered plants they had never seen before - knotweed, of course.

[@CloverPickingHarp]

Im in NH and have this EVERYWHERE on my property... i ended up excavating a big area of it but it is going back mightily already. If i want to treat it and you say late fall maybe 2 weeks before first freeze... when would be a safe time to start treating... October?

[@GreenShoots]

October is probably a safe time for you to start your treatment (depending on your elevation). Pay attention to the knotweed flowers on your property or in the area. I would start treating after they die.

[@bkgirl76]

Thank you for this overview! If a few small knotweed shoots come up in spring after a previous fall treatment, would you recommend digging the crown out or letting it grow to re-treat with herbicide next fall?

[@GreenShoots]

You are welcome! I would dig at least through the spring. Then, you can either let the knotweed recover enough so you can treat the foliage in the fall, or you could keep digging through the end of the year. Of these two options, if you can keep after it, I would lean toward digging.

[@GreenShoots]

I should have mentioned, check out our new KZbin video on excavation: kzbin.info/www/bejne/oWi6mHqIntSXf8U

[@greglloyd2377]

Great content!! Thank you.

[@GreenShoots]

You are most welcome. Thanks for your support!

[@YellowStickerGaming]

Thanks for this video! 2 questions 1. Do you have any thoughts on stem injection vs foliar application? I have a patch of knotweed about 500 sq ft in my backyard, and I'm trying to plan for the most effective possible herbicide application, even if it takes days. 2. I just bought this house -- I know the previous owners were very against herbicide treatment. Most of my knotweed is localized to the edges of my property, but there are individual straggling crowns toward the center of my lawn. Is it better to let them all grow so that the herbicide treatment in the fall is maximally effective, or is it possible / advisable to remove the rhizomes from these straggling crowns in the center now so that I can use that portion of my yard?

[@GreenShoots]

Based on your description, I would not do a foliar spray of foam or liquid because the knotweed stems are so dispersed. Injections are very effective, but you should wait until autumn to do injections. (We will be offering an injection system soon on our website.) In addition, you need a method to treat the stems that can't be injected (under 1/2 inch). For those uninjectable stems, do a foam wipe of the stems and leaves. Alternatively, if you need/want to treat earlier than in the fall, you can do a stem/leaf wipe in mid summer and then again in the fall. For the knotweed in the middle of your lawn, yes, you can dig those out. See our video on digging knotweed: Control Knotweed by Excavating or Digging Crowns kzbin.info/www/bejne/oWi6mHqIntSXf8Usi=4v5frUOC7vwj6qOY

[@GJ5570]

I got rid of all my knotweed, dug it up, and burnt it all up. It still came back, but just a few shots, just kept poisoning it. After 3 years, it was finally gone.

[@GreenShoots]

Congratulations! That's a big deal.

[@1918B]

Hi there - thanks very much for your video. I have a small infestation of around 4 stems in a very coveted part of London. I poisoned about 5 years ago and this is the first I’ve seen of it since its last treatment, the neighbours have built a wall and disturbed the ground which is why I think it has returned. When I treat this new growth, should I dig it up after the herbicide or should I leave the soil alone? I don’t want it to spread to the neighbour. Thanks!

[@GreenShoots]

Hello! Actually, with such a small infestation, you could probably dig it out. Here's our video on this. It gives guidance on when to dig and when to combine digging with herbicide treatments. The most critical thing is properly disposing of excavated knotweed crowns. Control Knotweed by Excavating or Digging Crowns kzbin.info/www/bejne/oWi6mHqIntSXf8Usi=4v5frUOC7vwj6qOY

[@mkemalsimsek]

what we need to do after autum herbicide. they are dried out, do i need to cut off or dig them out or leave as it is to wait spring. any body knows.

[@GreenShoots]

Yes, you can cut off the brown aerial shoots anytime. I would wait until winter (or a dry stretch). They will dry out more and will be easier to break off. Don't dig out the crowns. The herbicide applied in the fall may not fully circulate until a month or so into the spring.

[@anniebee760]

Really great information and presentation. Questions: what type of herbicide do you use on the knotweed? Thanks so much

[@GreenShoots]

Thank you so much, Annie! I'm sorry I should have mentioned the herbicide I typically use. I use glyphosate. It's quite effective and is relatively easy for the general consumer to use. On occasion, I use imazapyr. However, I do so only rarely and only when there are no desirable species nearby since imazapyr is so persistent in soils and could be taken up by those desirable plants.

[@anniebee760]

@@GreenShoots excellent 👌 thanks so much

[@silekiernanphotography]

@@GreenShoots Isn't glyphosate the active ingredient in Roundup, which everyone agrees is deadly dangerous for humans.

[@GreenShoots]

@@silekiernanphotography Yes, glyphosate is the active ingredient in Roundup. I would note a couple things. First, glyphosate is not very acutely toxic. Thus, it only receives a "caution" warning from U.S. EPA. (Horticultural vinegar on the other hand receives a "Danger" signal word because it is corrosive and causes severe eye injury.) Second, the IARC has found glyphosate to be a "probable carcinogen." Since that finding however no federal regulatory agency in the world has agreed. But, let’s assume glyphosate is a probable carcinogen. Go to the American Cancer Society website and look at the lists of “known” vs “probable carcinogens.” Alcoholic beverages and solar radiation are known carcinogens. Red meat is a “probable” carcinogen. These are substances which people intentionally consume. Therefore, if I try to minimize my exposure to glyphosate by using basic protective equipment like gloves, I feel pretty safe. However, that is of course my calculus, and yours may be different.

[@brockmcintosh4508]

​@@GreenShoots Another factor in the calculus is the impact that knotweed can have on its surrounding ecosystem when glyphosate is seemingly the only really effective way to eradicate it. I live in Montgomery County, Maryland, where they banned glyphosate but made a handful of exemptions. Japanese knotweed is one of them.

[@abdullahshaik4784]

I left a invasive plant sit on concrete block for 3 years and it never died after that I burned it in barrels. Some species are highly highly invasive

[@GreenShoots]

Yes, they can be tough! Some of these plants like knotweed can go dormant and survive pretty extreme conditions.

[@williaml8474]

In my thinned stand ( injected the blue last fall), decided this spring to not wait on them as I pulled the garlic mustard. In late April, zone 7, after some rains, as strong shoots come up, I find that gripping the stems close to ground level and applying a steady pull can result in getting a lot of rhizome out with the stem. Then bang the earth clump a bit and leave it sitting on a nearby log to dry out. Maybe revisit another day to knock out some more earth for more drying. I dry the garlic the same way. Those that can't be pulled will be candidates for the blue in the fall. Have not seen any mention of this pull and dry method

[@GreenShoots]

That sounds promising, William! I think it makes sense in spring and early summer to excavate the knotweed crowns by whatever means. I usually suggest digging (especially for those of us with bad backs), but I am going to try your method too! One thing your method reveals is how poorly anchored the knotweed crowns are. This makes uprooting them easier than one would think.

[@SuperFeist]

After following your advice and treating my large knotweed stand twice in late automn, I seem to have good results. Untreated patches on properties in my area are already showing lots of knotweed groth. On my land, there's almost nothing visible. I do have some isolated, small shoots coming up here and there. I started to dig them out. However they do come up in areas where they're not close to the big woody crowns of past seasons but more on the side. When I dig them out, the roots don't seem to connect to a large crown or big rhizom. So I am not sure where / what do dig up. Check all seemingly inactive crowns from past seasons for buds? Dig out all remote stragglers? Both? Thanks for advice, already quite some progress made over here.

[@GreenShoots]

If you killed the big crowns with the herbicide treatment, you won't have to excavate them at all. Just leave them in the ground. Just dig out any crowns with green stems that are 6 inches or so in height. If the stems are growing out of small crowns some distance from the big old crowns, that's a very good sign and easy work. Usually, the remote straggler crowns are from rhizomes deep underground.

[@the-lonely-ous1767]

Thank you very much. I needed this!

[@GreenShoots]

You're so welcome! Good luck dealing with your knotweed.

[@willst101]

I've been dealing with a couple sizable JKW patches in my backyard for the last few years. re: digging up crowns, I've read that you should disturb the ground as little as possible because it only encourages growth. Is that not true prior to spring when it may still be dormant?

[@GreenShoots]

If you are dealing with an infestation that has not been treated with herbicide, I generally say don't dig or otherwise disturb the site until after that initial set of herbicide applications. Once you have treated that site (and one hopes killed the vast majority of crowns in the clone), I advocate digging starting the following spring to kill off the remaining knotweed. I say this for two reasons: First, after the initial herbicide applications, the knotweed does not seem to take up and translocate the herbicide as well. Second, stimulating growth at this point isn't necessarily a bad thing. Having the stand go dormant would be far worse. You want that plant to keep producing growth that you can dig up. This is further depletes the stored energy of the clone at a time when it's already weakened. I recommend that people stop digging in late spring to allow enough growth for an herbicide treatment in the fall. As mentioned in the video, you have to be very careful when digging to ensure you don't spread rhizome fragments.

[@willst101]

@@GreenShoots Right on, thanks for the explanation

[@GreenShoots]

@@willst101 my pleasure!

[@JayPoe80]

I’ve had very good success cutting it with a lawn mower and line trimmer. Large stand stopped growing within 2-3 years. For reference, this was on the coast of Maine.

[@GreenShoots]

You raise a good point - if a stand of knotweed is essentially integrated into a lawn and mowed regularly, you can control it. My guess is that your knotweed probably still has some live rhizomes underground after just 3 years of mowing, but if you keep mowing, all the knotweed will die off. Be very careful, however. Anyone controlling knotweed like this should not mow knotweed near water, ditches, or even on inclines that could move the cut knotweed offsite. Mowing is exactly what spreads knotweed in road ditches.

[@kimnilsson7501]

Nice and informative video. Now I know much better how to go from here, but it will not be an easy task. Late last fall we started to pull down a lot of JKW (a little part next to a road, that unfortenately belongs to our land - a bit from the normal one). There are now few new greens coming up, looking much better. We have never done anything, but the next buy neighbour could have done someting 10 yrs ago (it is on their land too). The first part was ok, but not the spraying last weekend (we'll do nothing more until late fall). But we also have municipality people with their rules, taking no consider -the want the sight to be clear for cars. Right now only wish we had some (blue) foam here in Sweden to add to the result. [also saw an experiment using the JKW plant sap mixed in to fool the plant to get the rest down. Something from Wales]

[@GreenShoots]

Thank you! You clearly have one of those situations where outside constraints make it difficult to deal with the knotweed. It sounds like you are not treating with herbicides this spring, which is a good thing. Although in my experience (and that of many other applicators), autumn applications are the most effective, mid-summer ones may also work well too if they are combined with a a follow-up in the fall. That is what Jones etal 2018 found. I am advising customers now to consider a midsummer and fall treatment if that works better in their schedules.

[@kimnilsson7501]

@@GreenShoots Thanks for your reply. Unfortenately, we did treating with herb... (spraying last weekend), didn't want to say that right out (but guess it was too weak - now we can not buy Glyphospate anymore, but still in house stock :-). But now stopped since we found your great videos. Will to do the real work in this fall, leave it as good as we can, right now. But if it grow too high, we have to knock it down a bit for cars/ppl be able to see driving out. I hope, as it sees right now since last fall, we can live without that part.

[@talkay78]

We have knotweed in the backyard but we have a small child and don’t want to use herbicides. Are there zappers that work for knotweed or other less toxic methods?

[@GreenShoots]

If you decide not to use herbicides, the best way to remove the knotweed is through excavation or digging. This works well for small patches. Just be sure to handle the excavated crowns properly so that they don't re-root.

[@johnmoyer5515]

What about other foiliage or trees intertwined when spraying

[@GreenShoots]

Timely question. I would not spray foam or spray drops onto knotweed with branches of desirable trees overhanging the patch (unless you have 10 ft clearance). Instead, I would do a direct application to the knotweed by wiping foam on stems and leaves or injecting. Check out this video too: Knotweed Control for Homeowners: 4 Tips for Success! kzbin.info/www/bejne/gnrThoureLppfac Also, consider trimming the branch if that's an option. Make the trim at least a couple days before you spray if the tree is close. Also, spray away from the tree and definitely don't spray in high winds.

[@johnjackson8561]

Knotweed is a very good medicinal plant. I recently got Lyme and it has helped immensely, luckily I didn't spray or kill it in my yard now I have a new found respect for something I thought was bad.

[@BornN2Grave1]

Funny isn't it? Everyone in the comments is trying to destroy it. I found this video because I am considering growing it for medicinal properties.

[@GreenShoots]

If you want to grow it as a medicinal plant read Kovarova et al 2010. Be aware that the researchers there were very careful to ensure that the knotweed they grew could not escape into the wild.

[@johnjackson8561]

@@GreenShoots I have two stands beside my gardens and luckily I have not sprayed them as they are beside my garden. Japanese knotweed may be " invasive" but it's truly a wonderful medicinal remedy for many things and needs to be justified.

[@SusanJudy-e5z]

Please comment on the best strength/dilution for foliage spray. We also inject large stems with glyphosate- is the strength/ dilution recommended the same?

[@GreenShoots]

If you are applying primarily to leaves, I would use about 2-4% ai with glyphosate. If you are applying primarily to stems (wiping) I would use 20% strength. With injection, use full strength and inject 3-5 ml depending on stem size.

[@SusanJudy-e5z]

@@GreenShoots Thank you. We have approx. a quarter acre of knotweed established in the 1930's as ornamental plants. I believe the older stands of knotweed present additional challenges to eradication. The rhizomes are deep and many.

[@GreenShoots]

@@SusanJudy-e5z Yes, I agree. You probably have some rhizomes that are quite thick and deep. I would try to do a foliar application this fall after flowering. You could also do injections or stem wipes. All of those are very effective.

[@williaml8474]

Adhoc using these supplies in summer 2 years back injected to stems 3 in from ground seemed to have good kill. Left with smaller population of stragglers. This fall did before frost, more systemically throughout the grove, also did injection, anything bigger than a thumb diameter. Want to knock back the clumps with 4-6 massive stems. Will see come springtime

[@GreenShoots]

The stragglers that are left after a generally successful herbicide treatment are tough to deal with, although clearly better than having large knotweed stems! Next spring, you might consider digging some of these out and then treating the knotweed again in the autumn.

[@piet.hettie]

Hello John, where I’m living (Netherlands) we don’t have foam glyfosaat. Could I also follow your protocol but inject the stems instead of foaming the leaves? Cheers

[@GreenShoots]

Yes, Pieter, injection works too. It does use a lot more herbicide, and it won't work on small stems.

[@AM-og6vo]

I have a large area of knotweed that was knock down by heavy winter winds looks dead eill it vmcome back only random stalks coming up. Ty

[@GreenShoots]

If you haven't done any kind of treatment, it is almost certain to come back. Knotweed is quite cold hardy.

[@AM-og6vo]

@@GreenShoots ty for info🙂

[@GreenShoots]

@@AM-og6vo Welcome!

[@brockmcintosh4508]

I just bought a new house with new sod, which I thought would be my only worry. The backyard came with a tiny downward slope in the back covered with mulch and some newly planted Emerald Green Arborvitae ‘Smaragd’ shrubs. Within a week, Japanese knotweed has appeared through the mulch and has grown about 2 feet. A handful have started to sprout through the new sod. I haven't mowed yet but have been watering it. Now I'm trying to figure out how to maintain the new sod and combat the knotweed simultaneously, and I'm paranoid about mowing. Before each mow, should I cut each stem as low as I can and immediately discard? I know herbicide is supposed to be applied in the fall, but what about for cut stems in the spring and summer if I have to mow? I also don't want to encourage the rhizome to grow horizontally under the sod toward my house looking for new places to grow, so feeling paralyzed here. As for the knotweed growing through the mulch, should I just leave it alone until fall? A few other government resources recommend cutting just the first week of June. Also I saw a video of yours from 4 years ago where you cut the stem and apply the foam there. Do you recommend just applying foam to the leaves now? @Green Shoots

[@GreenShoots]

Brock - that's a tough situation - terrible that somebody left you with that hidden knotweed. Send me an email at johnATgreenshootsonline.com and we can try to figure out what you should do.

[@JoshRock84]

I have two small areas of knotweed at my house in Bradford VT. I don’t suppose you’re in Vermont? One patch is pretty close to my well head so I worry about contamination of my well water with herbicide.

[@GreenShoots]

Not located in VT, but I will be visiting this October! The herbicide we recommend, glyphosate, binds tightly with soils, and the limited applications of herbicide you will need to do or have done won't affect your groundwater or well.

[@johnjackson8561]

Knotweed is a medicinal super food it has helped greatly with that my recent bout of Lyme disease.

[@GreenShoots]

I certainly have no expertise on whether knotweed has medicinal properties. If it were grown in a tightly controlled setting that prevented the spread of knotweed, I don't see why it couldn't be cultivated for medicinal purposes.

[@wm963]

Yes, an excellent video. It would be appreciated if you could acknowledge the academic work of Swansea University, who you quote. I'm Welsh, and I appreciate local academics who promote good Science, rather than their usual propaganda. I've treated, with stem injection, a 5mx5m stand of Japanese Knotweed the past 2 Septembers. Some shoots are now sprouting [April 2023]. I was planning to change tack and spray upcoming shoots with Glyphosate/Blue foam. You've explained how this would be futile. I'll wait until post-flowering and adopt a double-barelled attack, with focused spraying & more stem injection.

[@wm963]

BTW, has anyone noticed how a bonfire of dead woody JKW stems creates multiple small explosions?

[@GreenShoots]

Swansea University has done great work. Theirs is the most comprehensive study on knotweed anywhere in the world. I constantly return to their work for guidance. After having treated your knotweed in the fall, you are now confronting the ongoing problem of trying to kill off the straggler knotweed plants. I recommend digging out remaining knotweed crowns in the spring. I discuss this in the video in relation to problem 6. If you do this, as you probably already know, it is absolutely critical you dispose of the knotweed properly. In the U.K. you thankfully have pretty tight restrictions (U.K. wide?) on knotweed disposal. We don't in the U.S. Therefore I recommend people here gather the excavated knotweed crowns in a heavy duty plastic bag and "cook" them in the sun over the course of the summer. Stop digging any knotweed by mid-summer. Then in the fall, dump the knotweed crowns out, cut into them with a shovel to check for viability, and that's it. Then, also do the treatment as you mentioned above. Good luck!

[@jerrysmith3517]

would rock salt aid in the dehydration of the rhizomes ? surface application after roundup? its a gravel lot and we are not concerned about damaging any other vegetation?

[@GreenShoots]

I am glad you asked this because I do get this question fairly often. From what I have read, knotweed (at least some genotypes) are pretty salt tolerant. Even if salt could kill the knotweed, I would not recommend using it. Salt is very persistent in the environment. It can be washed to other locations. I do not recommend using it for any weed killing.

[@joshuabecker6799]

Have a basketball root chunk in asphalt, drilled holes; poured table salt then covered it to stew. Year later the center is dead but of course the edges are fine. Pick-ax or fire is next.😂

[@GreenShoots]

@@joshuabecker6799 good luck!

[@Omeomy]

@@joshuabecker6799Do as per instructions in this video. It works. I have read and seen everything. This is a good summation.👍🏻

[@SPLIFFZPUFFZ]

bro, thank you!! JKW is a beast.

[@GreenShoots]

You are most welcome!

[@vKarl71]

1. Don't mow it - it will only help the spread! 2. Covering it with a tarp doesn't work without extensive other layering strategies 3. Dont use herbicide early in the season - wait til fall (so the weed draws the herbicide down into the rhizome) and be sure to do it before a frost & 4. treat with herbicide twice. 5. Cutting in the summer only helps spread it !! 6. The year after first chemical treatment 7. Plant native plants 8. Knock down all dead stems the season before fall chemical treatment. 9. Worst mistake is to do nothing.

[@GreenShoots]

nice summary!

[@ethanfritz427]

How do i avoid mowing it when its all over the middle of the lawn?

[@GreenShoots]

The situation you describe is one where mowing could potentially be successful - where turfgrass completely surrounds an infestation. I have worked at a number of sites where mowing turfgrass at a rate one would normally mow one's lawn has kept invasive knotweed from further expansion. If repeatedly cut by a mower, the leaves of in a knotweed clump become small and the stems spindly. Plant parts from these deformed knotweed clumps seem unlikely to spread, especially if confined to a turfgrass area. (However, I have not seen any field tests that confirms this.) CAUTIONS: 1. Don’t mow knotweed on slopes, near water, when rain is forecast, or anywhere live knotweed plant parts could be washed away (e.g., a drainage ditch). 2. Carefully monitor planting beds and other non-turf areas where knotweed stems might pop up. 3. Use a mulching mower or a side exit mower with the exit pointed toward the knotweed infested area in the lawn. 4. Clean the mower deck and blades immediately after mowing the infested area. Periodically dig out knotweed crowns in the infested area. Be careful with the excavated knotweed crowns. These definitely would have the potential to re-root. Our video on knotweed excavation or digging explains how to handle excavated crowns and viable knotweed plant parts: kzbin.info/www/bejne/oWi6mHqIntSXf8Usi=4v5frUOC7vwj6qOY.

[@Mr.Philbert_Coffee_Esq]

I have tried adding compost on top of it and keeping it wet to drown the roots. So far no success stopping it. I'm going to try to burn it out by adding fertilizer now.

[@GreenShoots]

You are joking . . . right?

[@Mr.Philbert_Coffee_Esq]

@@GreenShoots yes LOL

[@GreenShoots]

@@Mr.Philbert_Coffee_Esq 🙂 I see so many videos and suggestions about using Epsom salts, etc., to kill invasive plants. I am unduly wary!

[@AttommicDog]

When I built my house a contractor had some loam delivered and it was full of knotweed roots and chunks. Took years of spraying, and digging to get rid of it all. Nightmare. Worst weed ever.

[@GreenShoots]

This sounds similar to a case in Massachusetts, Trites v. Cricones, where a property developer had to pay almost $200,000 in damages for, among other things, creating a nuisance by spreading soil contaminated with knotweed at a new development.

[@AttommicDog]

@@GreenShoots it was in MA actually, but I got nothing but a giant headache.

[@GreenShoots]

@@AttommicDogSounds like a big one. I think this happens quite often.

[@AttommicDog]

@@GreenShoots My friend, it was a nightmare. for 3 years of my life.

[@AttommicDog]

@@GreenShoots But I won the war!

[@alexblue6991]

Is this plant good for wildlife like birds and deer

[@GreenShoots]

Birds and deer seem generally uninterested in it. Bees are attracted to the flowers.

[@tasminwing8304]

What if you cover with concrete?

[@GreenShoots]

Ah! You would need a big concrete pad. Knotweed does so well at escaping to the edges of covering.

[@tasminwing8304]

@@GreenShoots what's your best tip to get rid of it fast

[@GreenShoots]

@@tasminwing8304 if you are located in the UK, I would say have it excavated by a licensed contractor. That's the fastest (but very expensive). If you live somewhere else, the U.S. for example, treatment with herbicide is quite fast. Check out this blog below where we describe all the different resources we have for dealing with knotweed. One of our new options is to treat in mid-summer and again in the fall. greenshootsnews.blog/2024/04/25/invasive-knotweed-green-shoots-has-new-products-and-resources-for-dealing-with-it/

[@beverlyp.4078]

I have a large hillside with knotweed infestation. It’s now the end of February. How should I begin to attack this infestation?

[@GreenShoots]

I would start by knocking down the dead stems from last year to improve access to the site. If the site is bigger than 10 by 10 feet, check out our video on controlling a large knotweed infestation: Control a Large Stand of Japanese Knotweed in 4 Phases, kzbin.info/www/bejne/j33SY2ujfcydfpI. If you have any other questions, Beverly, let me know!

[@honeysuckle-end]

Won't waiting for it to flower mean a risk of seeds spreading?

[@GreenShoots]

Glad you mentioned that. Knotweed in North America can produce viable seed (unlike in Great Britain). However, the vast majority of the spread is vegetative - either by extension of the rhizome or parts of the rhizome or stem re-rooting. You could clip off the flowers and dispose of them. The first year's herbicide application to the knotweed is so important because it can do the most damage. If it's done well, over 90 percent of the knotweed can be killed. Optimizing that application is the most critical. That's why I recommend applying herbicide after flowering.

[@honeysuckle-end]

@@GreenShoots Thank you for your reply. I'm in England and pretty sure the small area just outside my property must have spread from seed. There is a larger patch up in the forest about 100 or so meters away. Forestry have been informed and are apparently going to sort it. It looks like it has spread under the fence to a small patch of weeds on my side which someone has cut without my permission! Possibly to try to hide the fact it has spread from their side! They've already sprayed theirs. I'll wait for mine to grow back and set flowers but I may have a battle on my hands! Thanks again!

[@GreenShoots]

@@honeysuckle-end How and when knotweed spreads is a mystery. I was just at a site yesterday in an urban area - small patch. The knotweed has been there for at least 30 years (probably longer). However, it has spread very little. Nothing in the neighbor's property. Good luck in your battle against your knotweed!

[@NonieDeLong]

My property is bordered (fenceline) by 4 feet - 8 feet deep knotweed. I and 2 neighbours have yards that harbour it. I managed to keep it in check last year by not disturbing it. This year a neighbour cut it all down several times in spring. As with many trees, this caused suckers or runners all over my lawn. I'm sure fragments were spewed into the lawn also. Now it's taking over my lawn, foubling weekly. Pulling does not help. Neither digging or mowing. I am not for herbicides but I am going to have to this year or watch it destroy 3 properties and make its way around the neighbourhood.

[@GreenShoots]

The best way to attack this would be to kill the main stand this fall with herbicide. If that main stand of knotweed remains, it will, as you observed, continue to send out rhizomes, especially if it is cut or disturbed. Once that main stand is controlled, you will be able to keep it out of your lawn with regular mowing. If you get your neighbors' cooperation in controlling the stand, you can reign the knotweed in.

[@NonieDeLong]

Thank you. I don't know if the neighbour will consent on his side. Can I improve my site just spraying appropriately on my side in the target window?

[@GreenShoots]

@@NonieDeLong Yes, you can do what you describe. Here's what you might consider. Treat the knotweed you have this fall. Then, next spring (or even late fall potentially) consider planting something there to compete with the knotweed. Turf competes well in sunny locations. Just be very careful when you mow near the knotweed. Collect your clippings and make sure the mower deck is clear of knotweed fragments. I encourage people to plant native plants. You might consult local resources - extension services or even cities - which should have recommendations for your area. Be advised, however, that you will have to deal with some knotweed coming into your yard as long as the stand in your neighbor's yard remains. Good luck!

[@jerryclark5725]

I saw a man kill a knot weed patch by mowing. It was at least five seasons of mowing before I didn't see knotweed shoots popping through the grass. Knotweed, along with many invasives are good for the not so invasive honeybee. Knotweed is also a valuable medicinal.

[@GreenShoots]

Mowing can be arduous and requires repeated efforts. Think of all the pollution caused by and the hours required for 5 years of mowing every couple weeks. Just as important, this technique doesn't work if you are doing restoration work because you need to be able to plant something to compete with knotweed. Constant mowing prevents this.

[@amiensarabellis8391]

Do certain plants grow better against possible knowledge allelopathy?

[@GreenShoots]

You have stumped me!

[@sethmoking]

There's a new invention called Rootwave in Europe, but unfortunately, it could be many years before it's available in the U.S.

[@GreenShoots]

I have read a lot about the Rootwave and watched the company videos. As it becomes more established, I am sure there will be more anecdotal reports and independent studies on it. Very interesting!

[@YoeyYutch]

Here is a link to the source material shown at 1:30 from the New Hampshire Department of Agriculture: www.agriculture.nh.gov/publications-forms/documents/japanese-knotweed-bmps.pdf

[@GreenShoots]

Thank you for adding that link!

[@mwaldyke]

One thing I would add is to watch the periphery. Kill the new, small plants at the edge before they can get established. I am in the second year of treating a stand of knotweed with glyphosate. It has had a significant effect on the central infestation, but I recently found a greater number of new stems up to 80 or 100 feet from the central stand. The young plants respond well to glyphosate. You just have to be sure you get them.

[@GreenShoots]

Important comment. To my mind, how to deal with the stragglers after a largely successful herbicide treatment is a big open question: Is it best to treat the knotweed sprouts with herbicide as they come up? Is it best to dig them? Cut them? This is complicated by the fact that a knotweed stand seems to go into semi-dormancy after suffering a big injury such as one from a successful herbicide treatment. I like to dig knotweed in the spring up until about mid-summer, and then do herbicide treatments in the fall. This works well, but is it the best method? I don't know.

[@kimnilsson7501]

@@GreenShoots Good answer, but unfortenately not one whe want. But it is the hard truth: "I don't know",and we just know way lesser... Thanks for all of your expert advise, and actually this was one too....

[@GusPolinski13]

Why not just dig out the rhizome if you don’t mind the physical labor?

[@GreenShoots]

Yes, that is an option, especially for a small patch. I would recommend doing one year of herbicide treatments first for larger stands. It greatly reduces the amount of digging required. We cover this in another video: Control Knotweed by Excavating or Digging Crowns kzbin.info/www/bejne/oWi6mHqIntSXf8Usi=4v5frUOC7vwj6qOY

[@Balenza345]

I have knotweed. Been trying for years to eradicate it. Have been cutting off the stem in summer and pouring weed killer into the stem. Because I thought this kills off the root. If I understand the advice given here, spraying with herbicide on the leaves in the autumn means the herbicide will get transferred to the large roots below the ground more eficiently?

[@GreenShoots]

Yes, that's right. During spring and early summer, I recommend people dig out any knotweed they can. Glyphosate usually only does a top kill in the early part of the year. A foliar application seems to work best. Getting herbicide on the green stem helps too!

[@jackobrien4432]

Can you burn it?

[@GreenShoots]

Yes, once the stems or crowns dry out, you can burn them. If you are burning a stand, however, the burn won't do much for control.

[@kellysardella928]

Thanks to a builder destroying over 100 Indigenous trees Holly, Oak & various pines over 60yrs old some older by clearing 3 lots then mowing a small manageable knot weed patch leaving all cuttings now they are everywhere, even busting the asphalt at edges of properties. And tree of heaven as sprouted up providing homes for nymph lantern flies . Most frustrating part is he cant afford to build now yet his destruction has affected all of properties also all the hawks which kept rodents in check are gone because their homes were destroyed. Our gardens are all effected. Thanks for the info we have a battle ahead of us .

[@GreenShoots]

That is a very sad story. How short-sighted! I can't believe that the future buyers of that property would want lots without such beautiful native trees and some natural area.

[@AlsanPine]

or just allow the deer in. my deer here in n. idaho eat them and keep them from getting out of hand.

[@GreenShoots]

That's interesting! I haven't seen much evidence of any animals eating knotweed anywhere I have worked, but the deer have lots of other choices. If food options are more limited, knotweed may look good.

[@AlsanPine]

@@GreenShoots that is probably the difference. i live at the edge of town and the deer are city deer. they love to munch of knotweed as they pop out of the ground. i removed the fence and in 5yrs they eradicated it by continually eating them and not letting them grow up. slowly depleted the energy of the root system. i did have to wack it down the first season as they had already grown tall when i removed the fence.

[@GreenShoots]

@@AlsanPine Thanks for that bit of info!

[@williaml8474]

Knocking down the stems allows access to other invasive vines

[@GreenShoots]

William L - do you mean the knockdown of the dead stems at the end of the year? I assume not. The knockdown for creating access paths should be pretty limited.

[@williaml8474]

@@GreenShoots Did a knockdown, break in half, kick aside in dec, Jan, - whatever I see. Get to see the crowns better. Small ones might get pulled from the ground, park them on an elevated surface. Then I can cut porcelain berry vines closer to the root (in a future cutting apply the blue to them). For now my process. Assume the injection did what it could do before frost, now after freeze knock aside, open the view, beautify by getting rid of tall ugly brown canes.

[@GreenShoots]

@@williaml8474 Yes, I agree completely - Getting rid of dead knotweed stems shortly after they die (and before the snow flies if you have it) makes sense As you note, you can also treat other woody invasives in the patch if there are any.

[@mattharvey8712]

Bravo.......... knot weed.........I grow not grass............that's sound like nut and chocolate stuff......cheers

[@GreenShoots]

Cheers!

[@wishywashy1153]

Knotweed sucks... but in my opinion, mugwort is worse. It stinks and isn't fun to break in half like the knotweed.

[@GreenShoots]

I have not worked extensively on mugwort. However, foam herbicide might work well for foliar applications because it can more easily penetrate the hairy leaves.

[@Omeomy]

Fork! Did everything right except when I saw you mention the bag thing. Yup went right through the construction bags. And the ants did also! So Hells bells I have another little patch. But I would say We’ve knocked down about 50% since last autumns first go at it.👍🏻👍🏻🙏🙏🙏🙏🫣

[@GreenShoots]

Good luck - it sounds like you will get it under control this year.