Knotweed Control for Homeowners: 4 Tips for Success!

This video provides homeowners and novices with a highly effective technique for killing knotweed in 4 steps.
00:23: Most advice geared toward those treating large infestations.
00:50: Most people are dealing with a small plot of knotweed - about 15 x 15 feet or 4 x 4 meters.
01:33: Damage to dwellings and foundations is "extremely rare."
01:48: Knotweed damage is primarily to ecosystems, our yards, our gardens.
03:27: Different application methods include foliar and stem injection. These methods have shortcomings for homeowners and property managers.
05:32: In the past Green Shoots recommended a cut stem technique for small patches. Results aren't as good as they should be.
06:12: One alternative to spraying, injection, and cut stem is to use direct application techniques such as wiping.
06:33: direct application techniques such as herbicide wiping works especially well with systemic herbicides such as glyphosate.
07:21: Wiping foam herbicide on knotweed stems helps the user deal with tall knotweed stems.
08:43: Our trials on wiping knotweed stems with foam herbicide.
09:13: We used our small foam herbicide dispenser in our testing. This dispenser contains 140 milliliters or a little less than 5 oz.
09:58: Our foam wiping method of applying to the knotweed stems worked really well! Off-target harm was minimal.
10:10: 4 Steps to to a direct application such as wiping to knotweed stems
10:17: First, knock down the dead knotweed stems if you didn't do this already.
10:38: In terms of timing, do your treatments in the fall after the knotweed has flowered.
11:08: Second, mix the herbicide solution in the small foam dispenser. Mix 70ml of herbicide, 65 ml of water, and 5 ml of Blue Foaming Agent.
11:25: Third, plan your order of treatment of the knotweed - where you will start applying and where you will end.
12:01: Fourth, you can do the direct application in different ways - by applying the foam herbicide directly onto the stem with the nozzle of the dispenser.
13:13: A variation on this technique is to use a rubber glove to wipe the foam on the knotweed stem.
13:36: Still another variation is the drizzle technique. This works well for small, low-lying knotweed plants - the kind that grow in the year following a good treatment.
14:15: I estimate that the direct application of foam including foam wiping uses about half as much herbicide as stem injection.

[@danmoehagen7376]

After years of trying to get rid of my knotweed, including the cut/foam method, I used the Greenshoots foam sprayer last fall on a 25' x 15' stand of weed. This spring, only 5 shoots came back and I hit them with foam after they had a few mature leaves. At this time, that entire stand is dead. I have a much larger patch to do this fall, but at least I know this works!

[@GreenShoots]

That is so great to hear! Good luck with that larger patch too!

[@TheRyano4ever]

Absolutely superbly researched and justified information. Clear, in depth and straight to the point, no messing around with trivials... Thank you for your professionalism regarding this topic, as many do not state clearly enough the details and methods required to remove this frustrating species.

[@GreenShoots]

You are most welcome, and thank you so much for your support!

[@YellowStickerGaming]

Hi John -- what does the timing look like to remove the dead stems AFTER the herbicide application? Are we safe to do it right after the first frost, or should we wait until the spring?

[@GreenShoots]

I would wait until the stems have died back completely. If the stems don't snap off, wait.

[@JJBeauvais]

We have a .56 acre raw plot on the edge of a coal region Knotweed everywhere, covering 40%-55% of the property We bought the blue foam agent today and the precision applicator plus we bought a 2.5 gallon jug of the concentrated glyphosate 41% Our stands are 15 feet tall but we plan to use ladders to spread it out across all stems. We also plan to use the coated stem plan for the taller ones. Thanks!

[@GreenShoots]

I wasn't sure from your comment if you are starting your treatment now, but it's a good time to note - a person will have much better success if they wait until later in the fall to do the application. Understandably, people with a new piece of property want to start working on it asap. But waiting a month or two - until after the knotweed flowers - can make a huge difference in the results. All the best in your work on the knotweed!

[@JJBeauvais]

@@GreenShoots thanks for this reply. We were planning on starting treatment in our 17901 PA zip code during the final week of August. Question: the flowers have arrived but they are still attached. Would you recommend I wait for them to fall off?

[@GreenShoots]

@@JJBeauvais Yes, I would wait until after the flowers have fallen off.

[@JJBeauvais]

@@GreenShoots ok! Thanks! Well sad news I’ve already treated it two days ago with the flowers on. Is it okay to go ahead and start the treatment over in two weeks? I’m thinking a second and third treatment using your 2-3 week method. What are your thoughts about this? Thanks in advance

[@GreenShoots]

@@JJBeauvais Sorry - I just had a busy stretch. I would do a second application. You could consider a 3rd another two weeks out, but only if the knotweed is still green.

[@knotweedkninja8539]

Use Glyphosate, (never use RoundUp brand). 2 ounces per gallon, 1 ounce of a sticker/adjuvant. Cover all surfaces of the plant. The silver bullet is to wait for the herbicide to be absorbed and then SPRAY IT A SECOND TIME! This is the only way to get 90 - 100% die-off in one season's treatment. DO NOT SPRAY NEAR ANY WATER. If growing beside water use the cut stem application. The most optimal month to treat knotweed is in September after the blooms and bees are gone!!!

[@MegaHealer]

Thank you

[@evidencebased1]

Can you elaborate on what is the “cut stem method “ ? Thank you

[@williaml8474]

I like the thought of putting it on the stems. Will try as an alternative to injection that I have been doing. I had best effect on large crowns last fall when injected closer in time to the post flowering time, than to frost time. I used a fan application pattern on the stand I mess with. Start from a location and go straight thru the stand. Then on another day from the start point pick a different angle. Etc

[@GreenShoots]

William, please let us know how stem wiping works for you! Also, that's interesting that you had better success with your application nearer post flowering time than to a time near a killing frost. What's your theory on doing the application to the same stand from different directions on different days?

[@williaml8474]

@@GreenShoots I try to spread out the work. Do 15-30 minutes per day. Do a straight line each day. I think I went up the center first, then lines off center. Maybe a wipe down of a stem section, thin or thick with coarse sandpaper , followed by a dribble line of blue, and finishing with spreading it out with a paint brush. I had wondered if I was injecting too much. I would stop when it oozed back out. Had wondered if just applying it on a thick stem where I cracked open the wall with a soil knife might be sufficient. Will try the wipe process in a few days for practice. I also have access to another stand that is a combo - knotweed and tree of heaven. For the heavens would follow your spaced cuts method. Pulling out shoots of knot is satisfying, but amazing how quickly new replacements come back, ugh. Some pulls though I think help finish, fully uproot, crowns given the blue last fall.

[@GreenShoots]

@@williaml8474 I love that you are trying different things. I too tried applying to a few stem cut open with a knife. Unfortunately, the conditions weren't well controlled, and didn't give me a strong indication of whether it helps. Knotweed and tree-of-heaven - that's like Godzilla vs. King Kong. That will be quite an achievement if you get that area under control!

[@svg001]

at about the 8:00 minute mark, you mentioned Tim Miller from Washington State U. wiped plant with three herbicides, including glyphosate--what were the other two (you glossed over them)? thanks

[@GreenShoots]

He used glyphosate, imazapyr, and triclopyr. Of these, triclopyr is the least effective.

[@kaylynanderson2187]

Excellent instruction. I have 1/2 my backyard proper, plus along the creek in the back and side of my property. I'll be injecting glyphosate directly. I noticed you said to inject into the core. However, I also heard of injecting into the phloem. What is your take on this? I'm purchasing glyphosate this next month (August 2024). One quart (5 ml each) covers approx 183 stalks. I'm using a 10% waste coverage (approx 175 stalks). Thank you for the excellent presentation.

[@GreenShoots]

Inject the glyphosate herbicide into the hollow core of the knotweed stems. When injected there, the herbicide will be absorbed into plant tissue eventually making its way to the vascular bundles in the knotweed stem which contain the phloem. These vascular bundles are minute so you really can't inject into them. The amount you inject depends on the strength of the glyphosate concentrate you are using. Since you are near a creek you should be using an aquatic approved glyphosate concentrate which contains 53.8% active ingredient. Research indicates you can use 3 ml of this aquatic glyphosate and be just as successful. I hope this helps!

[@kaylynanderson2187]

@GreenShoots , thank you for the information. I have 53.8% glyphosate but don't know whether it's aquatic. I had been using 5 ml but will finish with 3 ml. I have a lot of "babies," too. I'm wondering if it would be effective to prune the small ones and inject into the core immediately. What is your advice?

[@werther5952]

Thank you so much for making this. I have several small clusters of stems in my yard (about a square foot each), along along with some smaller plants that seem to spring up in the surrounding 20' - 30' or so. This spring, should I allow the plants to grow to maturity so I can apply herbicide in the fall? Or is there any proactive treatment I can do in the early part of the year?

[@GreenShoots]

You are welcome! In the spring the only thing we recommend doing is digging out the crowns (where the stems come out of the ground) if you feel ambitious and are capable of doing that. Just be sure to dispose of them properly. If you do excavate the knotweed crowns, then treat any new sprouts in the fall.

[@kristenbrasil]

I bought the Green Shoots foam kit and feel ready to take on the knotweed that is growing under my house and next to a paver patio thanks to your videos! The area was covered with knotweed before we put the patio in and it is still prevailing! I am nervous to use glyphosate but it seems like the foam won't effect other plants while getting rid of this horrible invasive. Can I throw out the plant in a black garbage bag once it is dead?

[@GreenShoots]

I wish you success with your knotweed! I would also use basic rubber gloves when you are applying. With the plant parts in the garbage bags - are you talking about the dead stems after a treatment? If so, once they are completely dead, you should be able to dispose them how you would normally dispose of yard waste.

[@greenabundancebydesign]

Excellent as always John. Thank you for sharing your information!

[@GreenShoots]

Thank you, Andrew! I am sure you are as busy as ever ridding the Boston area of invasive weeds!

[@volcomdc8351]

We recently found some of these sprouting in our yard and started freaking out... at max, they are 1-3 feet tall but a lot of them are inches/sprouting. What is the recommended treatment for these? Foam or foliar application? We haven't dug anything and are just a little confused about what to do right now since a lot of the advice seems to be for full-grown patches.

[@GreenShoots]

It doesn't help to treat with herbicide in the spring. You can dig or excavate. We have a video on doing that: Control Knotweed by Excavating or Digging Crowns kzbin.info/www/bejne/oWi6mHqIntSXf8Usi=4v5frUOC7vwj6qOY

[@radharcanna]

This information is extremely helpful. Thank you very much. Is it possible to eliminate knotweed entirely from a garden?

[@GreenShoots]

You are most welcome! This is an important question. Killing almost all of the knotweed (99.5%?) can definitely be done. You can control invasive knotweed to an extent that it has virtually no effect on the plants or wildlife in your garden. Moreover, managing the occasional knotweed sprouts from then on is easy. However, it can be very difficult to completely eliminate it. I mostly work in natural areas. In these areas, it's very hard to eliminate the knotweed entirely because native foliage will hide the small knotweed plants until autumn. If you have a more intensively managed garden, you stand a much better chance of totally eliminating it. For example, knotweed is not a problem in agricultural fields in the U.S., unlike other invasive perennial plants like Canada thistle or bindweed. To my mind, total elimination should not be the objective with the tools we have available to us now. Instead, control knotweed to the extent that it won't spread and will have an insignificant effect on the ecology of your garden.

[@radharcanna]

@@GreenShoots That’s fantastic. You’ve put my mind at ease about the problem.

[@GreenShoots]

@@radharcanna Great to hear that!

[@larssinke9505]

Is there a good alternative to glyphosate? It's banned where I'm at

[@GreenShoots]

Unfortunately, there really isn't a good alternative to glyphosate for the average consumer. There are other chemicals that professionals use but they have their own set of drawbacks. I would suggest excavation as the next technique. Start in the spring. The rhizomes are easiest to excavate at that time because the roots have not fully developed.

[@koenboone]

glyphosate is illegal in most countries by now....

[@TheJohnFry]

What if I scraped or cut the side of the stem before applying the roundup?

[@GreenShoots]

You could definitely do that. The vascular system is pretty near the surface, so you wouldn't have to scrape much.

[@kaylynanderson2187]

@@GreenShoots, Could I scrape AND inject into the vascular system? I'm purchasing glyphosate in a couple weeks (43%-48%) and will be using full strength. I intend to use syringes & needles. Will this be a problem for me?

[@karunald]

So for non-foam foliar application. About a 50/50 ratio of 41% Glyphosate to water? Which is actually a 20% solution? Is a surfactant needed? I don't have it but a friend wants to help a neighbor with it. I've never seen these guys.

[@davearrigg734]

@@GreenShootswould round up 18% concentrate of glyphosate do fine? Should I mix with water or spray directly?

[@karunald]

@@GreenShoots It's all kind of confusing - the data. I read 2% solution and the thinking you don't want to fry the leaves before the Glypho gets into the roots, etc. I have Goutweed/Bishop's weed I'm battling and kind find a tried/true protocol for that either. I see people struggling in FB groups/forums with people randomly trying various doses - many to no avail. Extensions etc. really need to get specific on instruct. EVERYwhere I go they say "Glyphosate" but never a %

[@GreenShoots]

I deleted my previous reply because I misread this question. If you are doing a foliar application with glyphosate, i.e., spraying foam or liquid onto the leaves and stems, you would use a solution with 2-3% active ingredient. If you are doing a direct application to the stems with our foam herbicide, for example, you should use a stronger formulation with 20% active ingredient.

[@GreenShoots]

@@karunald For most foliar applications, yes, a 2-3% active ingredient mix is right. For plants with tougher leaves and thicker cuticles you can go higher, but for plants like goutweed or knotweed with more delicate leaves, a lower amount of active is advisable.

[@karunald]

@@GreenShoots Thank you. Been battling Goutweed for 20? years? Never once heard about Fall treatment. So far I'm still digging and being methodical/anal. Anything that comes up should just be a 'piece' - anything beyond that - Spraying. I just REALLY want that to work cuz It's failed me at 2% area doses. It's a rough one.

[@suraya1224]

At 5:50: & at 10:13 important info! Wait to trwat until aft knotweed has flowered (fall, but b4 a killing frost)

[@GreenShoots]

Yes! Thank you for emphasizing that.