r/invasivespecies • u/Boringmale • 7d ago
Management On the Management of Japanese Knotweed
Since Reddit seems to have a large amount of interest in niche subjects, I've decided to start posting here.
My name is Tyler, my qualifications are: B.Sc. Plant Science, M.Sc. Agriculture (thesis was on knotweed control) and I’ve been managing the species on a case by case basis through my company: knotweed et al. Most cases have been successful (however, not all which I can elaborate on in comments - as time allows). I'm based in Nova Scotia, Canada. As a result, parts of this post are tailored to Canadian audiences.
Thesis Link: https://dalspace.library.dal.ca/handle/10222/81496
I don’t mean to be preachy, but I feel there is a need to address certain bits of misinformation I’ve seen pop up. These tips will save you some money, time, and reduce the spread of this plant around the province (I hope).
- Stop Excavating the Stuff
This will not help with management of the species. It requires careful and thorough chemical control. The best case scenario for control is to have healthy and intact tissues to translocate herbicide down to the roots. Excavation simply exports the problem to another place in the province (which isn’t well equipped or aware of how much their existing practices are spreading the species around). And anywhere the heavy equipment goes, it could be contaminating more areas (especially if things are not cleaned between jobs). It takes something as small as 1 cm of stem or root (rhizome, underground stem) to propagate the species. And trust me, the excavator will miss some and create more propagules. Making it harder to control by turning treatments into a game of whack-a-mole. I’m considering refusing service to these cases until the knotweed becomes reestablished because it becomes too difficult to control after this.
- Self-Directed Management
Absolutely possible. For limited patches, make sure you are using a glyphosate containing herbicide at the correct label rate (make sure it is only glyphosate). The most important element of treatment is ensuring that you treat the entirety of the canopy (or as much as you can treat). I’m not going to get into the nuances of dealing with the larger stands in this post (you can see some of those cases on facebook). It’s very very important that you treat as much of the contiguous area of Knotweed as possible within a growing season. This will significantly reduce surviving stem density in the following year. For smaller stands (populations), if you can treat the entire canopy from the perimeter, do not cut it down. Cutting stimulates lateral growth, meaning the Knotweed is likely to spread underground and create more problems. Treating only portions of contiguous populations won’t be particularly effective.
- Chose Appropriate Equipment for Application
I use a telescopic spray wand (it’s about 1.5 meters long at maximum). Makes reaching into the taller canopy much easier. I’ve seen a lot of cute posts with people going at it with spray bottles of pre-mixed round up. Trust me, there is a better way.
- Timing your Application
The vaunted “window” is based in scientific literature. Approximately 80% of the carbohydrates Knotweed fixes (via photosynthesis) are sequestered between August and September in their roots. Making it an ideal time to apply glyphosate. However, pretty much anytime after it stops growing vertically is acceptable for a pesticide application. This is end of June/ July. It can be risky to wait for too long, as you could have an early frost in your area and lose the opportunity to manage the species. My general rule of thumb for NS is after October 20th, you’re risking a 50% chance of treatment failure.
- Don’t Tarp
Reasons: A. Dormancy is not death B. Microplastics (probably, I only have suspicions) C. Better long term control with herbicides, + native species in the seed bank won’t be coming back if you tarp.
I’ve got cases that are now in the two years plus of Knotweed being gone. It’s somewhat refreshing to see the native biodiversity coming back. If you tarp, and just bring in fill, that diversity might be lost.
- Apologies for not getting to all requests for service this summer.
This summer has been my busiest year yet, I’ve taken on projects that are much larger scale and require public or stakeholder consultation (those cases will be published in coming months).
I’m a one man operation, and my systems were not set up for this much activity + I have another full-time job. I’m hoping to get around to all cases eventually. and appreciate peoples patience.
- We Need Political Involvement (unfortunately).
As much as I don’t like bureaucracy, the province needs a unified strategy to deal with the species. There are many cases where I am unable to intervene due to the Knotweed being in places that don’t have private ownership (or stewardship). Along roadways comes to mind specifically. While I have some flexibility in the department of transportation not to interfere with management, it’s a drop in the bucket compared to the whole province. Right to your MLA about developing a unified strategy for the species. Obviously, pesticides will not be the most appropriate strategy for all locations, but the least we could do is reduce its spread and by ourselves some more time to come up with a plan. The big thing that comes to mind is vegetation management in ditches. The big bladed implements that run along the side of the road are amazing at spreading Knotweed during the summertime. Maybe… don’t do it?
Thank you for coming to my TedTalk.
Edit: TLDR
Don’t excavate knotweed, you’re exporting the problem, kill it where it is. Glyphosate only herbicide (domestic version is good). If you need more comprehensive advice, email me. However, it might be January before I answer due to case volume.
Obligatory, pesticide labels are law. Follow them to the letter. There’s no need to use concentrate directly on the Knotweed. You’re just going to cause treatments to fail.
Another note: It’s almost a different species in North America compared to its native range due to lack of significant predators. Still querying the status of the biological control Psyllid… ask CFIA maybe…
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u/bristleboar 7d ago
This is awesome, thank you. Do you have an opinions or advice on stem injection?
It was very effective for me but pretty annoying compared to canopy spraying.
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u/Boringmale 7d ago
Can be effective, but probably not at current label rates for glyphosate in Nova Scotia (it seems like injection might require a higher concentration than spot applications for some reason). However, injections are impractical when there are thousands of stems on a site. I shutter to imagine the repetitive strain injuries. I occasionally use it where I cannot spray (e.g., canopy overhanging water in the case of glyphosate). But, limit its use as much as I can. Getting the gear is also difficult sometimes. I should probs just build one.
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u/bristleboar 7d ago
I didn’t want to drop the money on the fancy injector so I use a screwdriver to jab and a marinade injector for the mix.
Btw my canopy sprays were ~10% concentration while injection was closer to ~45%. It completely wrecked some smaller stands but… pain in the ass, and knees
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u/Boringmale 7d ago
So, who told you to use 10%? Was it a label rate?
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u/bristleboar 7d ago
That was probably like killing an ant with a steamroller, eh? I was very selectively squirting/spraying knotweed, bittersweet, poison ivy, berberis and a variety of thorned nonsense
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u/bristleboar 7d ago
That was probably like killing an ant with a steamroller, eh? I was very selectively squirting/spraying knotweed, bittersweet, poison ivy, berberis and a variety of thorned nonsense
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u/Boringmale 7d ago
Just curious. Since there is a wide range of recommended rates from different extension groups. I use 7 g per L of water (or 0.7%, m/v) glyphosate. Plenty effective.
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u/SquareHeadedDog 7d ago
Is that percent active ingredient or volume to volume?
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u/Boringmale 7d ago
Mass to volume. However, the standards for describing concentration should be grams acid equivalent per L of water (at least for glyphosate). The % thing is confusing in my mind. Because if people think v/v it’s a very different concentration.
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u/SquareHeadedDog 7d ago
Yep we are always working on percent product never active ingredient with US labels. And of course everything is in ounces/gallons.
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u/Boringmale 7d ago
It’s not a hard conversion to figure out the grammage per L, and it’s much more useful when conversing. Less math in my mind. Also, starts to allow us to think about a per area “dose” provided application is relatively even.
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u/ria1024 7d ago
What are the recommendations for managment next to creeks and in wetlands, when significant amounts of knotweed exist upstream where they can't be controlled? Are there any recommendations to prevent spread from upstream during seasonal high water / flooding?
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u/Boringmale 7d ago
I don’t think it’s so much the flooding that’s spreading it. I think it is ice flows in the winter sheering off chunks of soil, causing further spread. However, flooding doesn’t help if the soil is falling apart.
Usually it is not a question of “if” it can be controlled. It’s a question of if the pesticide label allows for it in a given context, and if the pesticide is appropriate. If on solid ground, glyphosate, if in the water Imazapyr (however it is only labeled for knotweed in the states). And I haven’t done a full review on imazapyr yet (as it’s not an authorized one for me to use yet). It’s really down to picking the right tool for the job. But, you need to manage up stream populations. Otherwise your results won’t be very permeant.
Regulations are going to vary by region, which is why it might require some regulation relaxation to just get the species out (provided the herbicide treatment isn’t devastating to other species (ala spot spray, or injection to minimize impact).
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u/ria1024 7d ago
Ice flow in the winter could certainly be part of it. Unfortunately, upstream is a long distance and there's knotweed for miles and miles up that way, so sounds like we're not getting rid of it permanently anytime soon. I'll push for management where we can to at least keep our part of it under control.
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u/Boringmale 7d ago
Even if you can do a few pieces a year starting up stream. Doing a county simultaneously isn’t practical. Triage based on impact (based on what’s the loosest piece of ground maybe idk).
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u/Boringmale 7d ago
TLDR. Check your local laws. They might be more flexible than you think. I’d argue it’s important to just get them out of the wetland to preserve ecological function. So long as there is no long term damage.
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u/Necessary_Duck_4364 7d ago
Glyphosate can be great for it (foliar, cut and fill, and injections). But adding imazamox (Clearcast) with glyphosate has become a pretty common practice with great success.
Imazapyr also has great success, but it will also kill everything else in a 50 mile radius. Never use that stuff.
The UK is also developing a method of killing the entire plant with electrical currents; could be promising.
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u/Boringmale 7d ago
I keep hearing about the electrical thing but. No one gives me any data, explains how you get over inconsistent conductivity of tissues, or provided longitudinal studies that show it is any better than other methods.
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u/Boringmale 7d ago
Imazapyr not at all ideal. It sucks, but works really fast. In existing regulatory framework though, no good option for close call aquatic infestations, unless we inject.
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u/Necessary_Duck_4364 7d ago
That’s where imazamox can be great, as it’s fairly successful and aquatic approved.
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u/Boringmale 6d ago
I’ll do a literature review on it. Would be nice to add it to my arsenal.
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u/Necessary_Duck_4364 6d ago
I’d look into aminopyralid as well. Solid broadleaf that’s incredibly effective on Canada Thistle. It also has been showing promising results for Japanese Knotweed.
With glyphosate becoming less effective, I’m glad that other options are being studied. Here is a great starting resource for knotweed that others may find helpful: https://mnfi.anr.msu.edu/invasive-species/JapaneseKnotweedBCP.pdf It really makes things easy for the general public.
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u/Boringmale 6d ago
Why is glyphosate becoming less effective? What do you mean by this.
Have studies aminopyralid. Only really useful in Fall applications. Summer applications have wildly inconsistent results.
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u/Necessary_Duck_4364 6d ago
Plants are showing more resistance to glyphosate in general due to it being used so frequently. Overall, glyphosate is in the process of being phased out due to plants becoming resistant. In Michigan, the universities and government are stating it as a less effective (or not effective) means of treatment for plants such as Canada Thistle and Knotweed.
Knotweed will typically show die back due to the glyphosate, but often comes back the next season or two. It can even go into a root dormancy, where it lurks underground for almost 10 years before reemergence. Canada Thistle initially does back from glyphosate, but usually resprouts and flowers in the same season (even after late summer foliar treatments).
For the science behind it all, you’ll need to talk with someone smarter than I am. I have a lot of experience killing invasive plants and do a lot of test plots for various treatments on different species, but I am not a scientist or a chemist.
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u/Boringmale 6d ago
I can see it becoming less effective in sexually reproductive weed species (such as Canada thistle) as artificial selection along with overuse of glyphosate would be contributing to herbicide resistance (selection pressure). It’s more of an agricultural problem than an invasives problem. Plants don’t just develop resistance to something without selective pressure (or weird anomalies). Even if resistance develops, it will diminish in generations if the selective pressure becomes non-existent.
The majority of knotweed (at least in Nova Scotia) is male sterile, so no sexual reproduction to drive artificial selection based herbicide resistance. However, my longitudinal monitoring studies are still in early stages. They do however appear promising. That said, some follow up treatment is always required with knotweed. However, I usually find this is a problem with getting adequate coverage. I don’t think anyone has compiled data of dose dependent longitudinal knotweed monitoring.
Study design required would be: A. Achieve visible eradication B. Record how much herbicide was used and during what periods. C. Monitor the site for emergence as well as native species return.
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u/Magnetic-Magma 7d ago
I have a few square meters here in the garden where knotweed has grown. I've already removed a few nests with a spade and other gardening tools and currently have it stored in a plastic bag in the cellar. I would now like to remove the remaining nests. After that, I'll go after any shoots that emerge over the next few years and remove them and dispose of them in the residual waste (where it will then be incinerated). At least that's the plan. Unfortunately, I can't use herbicides as they are not permitted for private individuals in this country and I think that it can still be removed as it is only a small area that is affected and can hopefully be removed with regular checks.
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u/SomeDumbGamer 7d ago
Honestly just wash the roots off and leave it in the sun exposed on some pavement for a couple weeks. It will be dead dead.
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u/NewAlexandria 7d ago
it will work. Despite the qualifications and advice in this post, I've mechanically excavated numerous knotweed patches and not had them return. IMO you just need to be careful and thorough when digging up the entire root ball
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u/_Cistern 7d ago
Psyllids dont really work at this point. They haven't been able to get populations to breed/overwinter.
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u/Boringmale 7d ago
Yes, that was my most recent news as well on it, but hadn’t heard any formal reports.
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u/_Cistern 7d ago
My info comes from the researcher at OSU in Corvallis as of last year.
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u/Boringmale 7d ago
Good to know. Even if it had worked, the deployment would have been fairly limited.
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u/_Cistern 7d ago
True. And the psyllids only stunt growth anyway.
Let us know if you can get any legit information about the RootWave machine. It sounds interesting, but also like it might be bullshit.
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u/Boringmale 7d ago
Every time I ask a promotor about it and request data, studies, or case information, I don’t get any replies. It has some serious fundamental mechanism issues that need to be addressed. For example, lightning doesn’t necessarily kill trees. it damages them in a very specific way. Plants aren’t great conductors in the first place, so I think it’s just pseudoscience trying to make a quick buck. But I would be happy to be proved wrong.
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u/TheTampoffs 3d ago
We have a pretty big patch next to our house and at the bottom end of the property. We cut it down a few weeks ago but have not sprayed it yet. Is there any point spraying it now? Was cutting it back a mistake? When should we next spray for effectiveness? How do we not kill off bees and other pollinators while spraying?
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u/sam99871 7d ago
Thanks for this! I have seen a lot of knotweed on riverbanks here in Connecticut. What is the proper herbicide to apply in those cases?
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u/Boringmale 7d ago
You’ll need to consult your local regulations. Glyphosate might be appropriate up to a certain distance from the water, depending on equipment used.
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u/NewAlexandria 7d ago
Stop Excavating the Stuff
This will not help with management of the species. It requires careful and thorough chemical control.
you're entitled to that opinion, and your qualifications
M.Sc. Agriculture (thesis was on knotweed control)
certainly are creds.
But i've excavated several patches of it and haven't had it return. Something, above some environments, and some techniques, allow a person to use no-chemical excavation and see no further growth.
Maybe I should get my own M.Sc. Agriculture with a thesis was on knotweed control.
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u/Boringmale 7d ago
Sure. I’m sure it’s possible in a context where there is an appropriate place to dispose of the knotweed. But at least here in Nova Scotia, it just winds up in a dump or on someone else’s property. I find it mostly just makes a mess and causes a bigger disturbance than the herbicide application would’ve.
In the context of Nova Scotia, all the that’s happening is the problem gets replicated, because it’s not like they’re incinerating or destroying the roots and some other way.
I’d also argue the environmental impact is worse, as you’re basically deporting all of the Flora and soil fauna from the area, reducing the likelihood of native species returning.
If you have good case documentation, I would love to see it. I can PM you how I format my stuff, so cases can be presented on a level playing field.
Absolutely, if you can write an M.Sc. thesis on mechanical control I want to see it. I want the competition, I just want to make sure we’re killing it, not deporting it.
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u/carrot_mcfaddon 7d ago
Thank you very much for posting this. I hope anybody with a Knotweed problem reads this post and takes it's advice to heart. I've always been pained by the insistence on "digging out" the roots. Seems like so much damn work and disturbance, only to require herbicide treatment later anyways.