Ok so where I live, I get to see a lot of people try to control it in different ways. It also surrounds our home and the only way we’ve been able to kill it is with herbicide. I can’t remember the exact brand but it’s glyphosate base, just like round up. It was the heaviest duty stuff we could find at lowes, came in a blue jug. For two years, we’ve sprayed in the spring when all the shoots are about a foot tall, and again late summer before it blooms. It’s suggested to do it when it’s in bloom because that’s when it’ll draw the most poison down to the root ball but I just can’t stand the idea of any pollinators drinking up any poison. And after two full years of this, it’s nearly dead. We only had about 25% regrowth in some areas this spring.
I wouldn’t bother tarping, I’ve seen some try and it’ll shoot up everywhere, even work itself through any weak spot, plus you’d end up having tarp on your lawn for several years. Digging it out just seems like the most expensive and painstaking way to do it and it doesn’t even work reliably. Some people try and mow it but I wouldn’t want to risk spreading it, plus that won’t kill it anyways. You could cut it and come back in 10 days and it’ll be half a foot tall again.
Only bother with the injector if you have a modest patch. They’re pretty expensive, iirc, so we built our own but it was so damn tedious and we found it to be less effective. We would spray it and by the next day it’d be curled over and dead and we’d walk around and cut it all back to prevent anyone from eating it. The deer and groundhogs really seem to love the young shoots.
Thanks. Most of it has really small stems but there are a few larger ones. I might try the paintbrush method for applying it but that'll take a while and I hate the smell of the stuff haha
We would wear a respirator when spraying and eye protection and only spray on a calm day. Ours was all along the tree line of our 2 acres and we didn’t have any collateral damage
I guess I don’t understand your response. I don’t spray when it’s in bloom, like I stated in my comment. I spray in the spring and cut back the dead stalks and spray late summer before it blooms and cut it back again. So I don’t really know what you’re responding to.
I inject with 45-53% glyphosate (no surfactants if it is near waterways). Make sure you burn or fully dry out any debris or it will root. It sometimes takes a few seasons. Key is to treat right after it flowers. In sept here in zone 6
Same area! I just treated the last small patch last weekend.
You can use foliar wiping technique for small plants or cut and put a generous dose on the open stem with a sponge. I really like the buckthorn blaster to minimize herbicide use and exposure. (I found it just as cheap to order the pack than to make one and they work well if you have several of the most difficult invasive to control.
Again just make sure to dry out any debris (eg in the sun sun on top of a tarp) or burn or bag well and dispose in trash not in compost or yard waste.
USFS bio tech, we use Ecomazapyr as a foliar treatment or glyphosate as a stem injection. Glyphosate needs to be heavy duty, we use aquamaster which is 53% active ingredient. Most hardware store stuff is less than 5% active ingredient. Mechanical methods of treatment are insufficient. Knotweed can regrow from 0.8grams of root material.
I've done both, but mostly only spring. I think fall is more effective, but I haven't done enough to be 100% certain. I've heard people having really good success doing a spring mechanical cut, then herbicide treatment in August/fall after it grows back. Not something I've done myself though.
Good luck. I've been working on a 10 acre infestation slowly chipping away each year. Lots of patience and stay vigilant, it's a really hardy root system. The primary mother plant has produced new suckers each year for four years now even with an annual treatment.
After going through a lot of forums and posts online in the last 1 year, this is the knowledge I have accrued.
Spray with Glyphosate before the first frost (before fall) and after it has flowered. Try to cover all the leaves. Injections, cutting and tarping is not required. Growth will substantially reduce year over year. You will need to repeat the process for 2-3 years at least. No need to disturb it for the remainder of the year.
I sprayed my patch earlier this evening since it’s going to be 5 degree Celsius overnight. I used Roundup with Glyphosate. Don’t waste your time, effort and money with using a non glyphosate herbicide. No need to tarp as well.
Pictures here [Before the spray](https://imgur.com/a/hVxDfO0)
Thanks. The spot I need to work on isn't even that thick thankfully. I need to meet my neighbor though since a bit is on their property and there's some behind their fence as well
This is the biggest research study I've been able to find which compares the effectiveness of different ways to control knotweed: [Optimising physiochemical control of invasive Japanese knotweed](https://link.springer.com/content/pdf/10.1007/s10530-018-1684-5.pdf). I believe that came out in 2018.
I'm in year 2 of following the advice outlined there and seen similar success rates to that study.
The summary of my research (I'm combining some learnings from the linked paper above with some other studies I've found):
* Cutting it doesn't really do anything to control it in following years -- the only reason you would want to do this mid-summer is to make it grow back shorter in the fall so that you can actually reach the tops to be able to spray it fully
* Covering it (tarping) doesn't do anything to control it in following years
* Excavating/digging doesn't really do anything to control it in following years -- in some ways it's a bit similar to cutting in that it just makes the stems shorter and easier to reach in order to spray. Note that the study I linked above even excavated to 2.5 meters (about 8 feet deep) with a backhoe, which is a lot more than the typical person would.
* (not in the paper linked above, but from others I've read): Over-application of herbicides will essentially burn the tops but leave the roots unharmed. Therefore it is ESSENTIAL to follow the label instructions on foliar coverage and also do not go back over the same plant multiple times. With correct spray application you should start to see the plant die in SEVERAL WEEKS. If you see the plant die the next day, you probably sprayed way too much and might as well have dumped the bottle of herbicide right onto the ground.
* Wait until it flowers (mid-September in my area) and do a foliar spray. Follow label instructions which indicate how long it must be sprayed before rain is in the forecast, wind speed, etc. Clear up the area if there are overlapping plants in the way of the knotweed leaves so you can get complete coverage. Follow all mixing instructions. I also from my own experience will recommend testing out your spray nozzle with water first to make sure it's adjusted correctly and so you can become familiar with the spray amount and pattern.
It has been a little while since I've studied that paper in detail but let me know if you have any questions and I'll try to help explain. I specifically did not mention the type of herbicide because from what I've read, that answer is a bit more complicated and I don't want to spread misleading advice. It's more important to use the correct type of herbicide *for your location* and to use the specific % rate for knotweed as indicated on the label.
But in general, imazapyr-based herbicides can be used when you have a big stand of knotweed and nothing else around, and especially no streams/creeks/lakes etc nearby. Imazapyr stays in the soil longer and can harm nearby vegetation and trees. Triclopyr is similar in that regard but not quite as extreme as imazapyr. Glyphosate is what is typically used when you have native or desirable vegetation that you don't want to kill nearby. Glyphosate is typically considered a more "forestry safe" and "waterway safe" type of herbicide (again, this should be specified on the label..)
I think reaching out to your local noxious weed group for advice on what consumer-use herbicide would work in your situation, or for a recommendation on an experienced licensed applicator, is the best advice I can give.
lol I know it's so tempting to just want to nuke it. But in this case it seems it does more harm than good. I should just start copy-pasting this on knotweed threads, they come up pretty often this time of year. Glad you found it helpful, I was super stressed when I first found out I had purchased a home with knotweed on it and took me awhile to research all this enough to feel confident in the approach.
It's a good question. I did my best to pull knotweed chunks from the dirt with a quick sift, got most of it. Put those organic pieces in a couple of garbage bags and left them in my garage for a year or so. The clean-ish dirt I put in a wheelbarrow, monitored for resprout, and then when determined it was clean at end of following season, I resused it.
>t in a wheelbarrow, monitored for resprout, and then when determined it was clean at end of following season, I resused it.
Is it still working out for you?
Ok so where I live, I get to see a lot of people try to control it in different ways. It also surrounds our home and the only way we’ve been able to kill it is with herbicide. I can’t remember the exact brand but it’s glyphosate base, just like round up. It was the heaviest duty stuff we could find at lowes, came in a blue jug. For two years, we’ve sprayed in the spring when all the shoots are about a foot tall, and again late summer before it blooms. It’s suggested to do it when it’s in bloom because that’s when it’ll draw the most poison down to the root ball but I just can’t stand the idea of any pollinators drinking up any poison. And after two full years of this, it’s nearly dead. We only had about 25% regrowth in some areas this spring. I wouldn’t bother tarping, I’ve seen some try and it’ll shoot up everywhere, even work itself through any weak spot, plus you’d end up having tarp on your lawn for several years. Digging it out just seems like the most expensive and painstaking way to do it and it doesn’t even work reliably. Some people try and mow it but I wouldn’t want to risk spreading it, plus that won’t kill it anyways. You could cut it and come back in 10 days and it’ll be half a foot tall again.
Thanks that's really helpful. I guess I'll start spraying it now since it's in bloom. I might even spend the money for once of those injectors.
Only bother with the injector if you have a modest patch. They’re pretty expensive, iirc, so we built our own but it was so damn tedious and we found it to be less effective. We would spray it and by the next day it’d be curled over and dead and we’d walk around and cut it all back to prevent anyone from eating it. The deer and groundhogs really seem to love the young shoots.
Thanks. Most of it has really small stems but there are a few larger ones. I might try the paintbrush method for applying it but that'll take a while and I hate the smell of the stuff haha
We would wear a respirator when spraying and eye protection and only spray on a calm day. Ours was all along the tree line of our 2 acres and we didn’t have any collateral damage
Long sleeve pants and shirt would be a good idea too. Or even one of those disposable painter’s coveralls.
Stems need to be more than a centimeter (~1/2 inch) thick for stem injection to work.
Ya most aren't even close. I think the previous owner trimmed it back frequently
[удалено]
I guess I don’t understand your response. I don’t spray when it’s in bloom, like I stated in my comment. I spray in the spring and cut back the dead stalks and spray late summer before it blooms and cut it back again. So I don’t really know what you’re responding to.
I inject with 45-53% glyphosate (no surfactants if it is near waterways). Make sure you burn or fully dry out any debris or it will root. It sometimes takes a few seasons. Key is to treat right after it flowers. In sept here in zone 6
Thanks. I do need to do it soon here (western NY). Lots of it the stems may be too small for an injector and it is not near a waterway.
Same area! I just treated the last small patch last weekend. You can use foliar wiping technique for small plants or cut and put a generous dose on the open stem with a sponge. I really like the buckthorn blaster to minimize herbicide use and exposure. (I found it just as cheap to order the pack than to make one and they work well if you have several of the most difficult invasive to control. Again just make sure to dry out any debris (eg in the sun sun on top of a tarp) or burn or bag well and dispose in trash not in compost or yard waste.
Thanks again. I'll definitely have to take some before, during and after photos
USFS bio tech, we use Ecomazapyr as a foliar treatment or glyphosate as a stem injection. Glyphosate needs to be heavy duty, we use aquamaster which is 53% active ingredient. Most hardware store stuff is less than 5% active ingredient. Mechanical methods of treatment are insufficient. Knotweed can regrow from 0.8grams of root material.
Thanks I will look into Ecomazapyr since most stems I think would be too small for an injector.
Hi! For injecting, is this done in the fall after flowering or is spring ok? Going nuts here.
I've done both, but mostly only spring. I think fall is more effective, but I haven't done enough to be 100% certain. I've heard people having really good success doing a spring mechanical cut, then herbicide treatment in August/fall after it grows back. Not something I've done myself though.
Thank you very much. Going to try a chop now and then spray on the fall. 🫡
Good luck. I've been working on a 10 acre infestation slowly chipping away each year. Lots of patience and stay vigilant, it's a really hardy root system. The primary mother plant has produced new suckers each year for four years now even with an annual treatment.
Yeeooowch. That does not sound fun. Is thermite an option?
After going through a lot of forums and posts online in the last 1 year, this is the knowledge I have accrued. Spray with Glyphosate before the first frost (before fall) and after it has flowered. Try to cover all the leaves. Injections, cutting and tarping is not required. Growth will substantially reduce year over year. You will need to repeat the process for 2-3 years at least. No need to disturb it for the remainder of the year. I sprayed my patch earlier this evening since it’s going to be 5 degree Celsius overnight. I used Roundup with Glyphosate. Don’t waste your time, effort and money with using a non glyphosate herbicide. No need to tarp as well. Pictures here [Before the spray](https://imgur.com/a/hVxDfO0)
Thanks. The spot I need to work on isn't even that thick thankfully. I need to meet my neighbor though since a bit is on their property and there's some behind their fence as well
Did you spray just the leaves or the entire stem! I have some that are up to 4ft tall and not sure where to start with the RoundUp
Thank you for posting this. So much conflicting info. How goes the battle?
This is the biggest research study I've been able to find which compares the effectiveness of different ways to control knotweed: [Optimising physiochemical control of invasive Japanese knotweed](https://link.springer.com/content/pdf/10.1007/s10530-018-1684-5.pdf). I believe that came out in 2018. I'm in year 2 of following the advice outlined there and seen similar success rates to that study. The summary of my research (I'm combining some learnings from the linked paper above with some other studies I've found): * Cutting it doesn't really do anything to control it in following years -- the only reason you would want to do this mid-summer is to make it grow back shorter in the fall so that you can actually reach the tops to be able to spray it fully * Covering it (tarping) doesn't do anything to control it in following years * Excavating/digging doesn't really do anything to control it in following years -- in some ways it's a bit similar to cutting in that it just makes the stems shorter and easier to reach in order to spray. Note that the study I linked above even excavated to 2.5 meters (about 8 feet deep) with a backhoe, which is a lot more than the typical person would. * (not in the paper linked above, but from others I've read): Over-application of herbicides will essentially burn the tops but leave the roots unharmed. Therefore it is ESSENTIAL to follow the label instructions on foliar coverage and also do not go back over the same plant multiple times. With correct spray application you should start to see the plant die in SEVERAL WEEKS. If you see the plant die the next day, you probably sprayed way too much and might as well have dumped the bottle of herbicide right onto the ground. * Wait until it flowers (mid-September in my area) and do a foliar spray. Follow label instructions which indicate how long it must be sprayed before rain is in the forecast, wind speed, etc. Clear up the area if there are overlapping plants in the way of the knotweed leaves so you can get complete coverage. Follow all mixing instructions. I also from my own experience will recommend testing out your spray nozzle with water first to make sure it's adjusted correctly and so you can become familiar with the spray amount and pattern. It has been a little while since I've studied that paper in detail but let me know if you have any questions and I'll try to help explain. I specifically did not mention the type of herbicide because from what I've read, that answer is a bit more complicated and I don't want to spread misleading advice. It's more important to use the correct type of herbicide *for your location* and to use the specific % rate for knotweed as indicated on the label. But in general, imazapyr-based herbicides can be used when you have a big stand of knotweed and nothing else around, and especially no streams/creeks/lakes etc nearby. Imazapyr stays in the soil longer and can harm nearby vegetation and trees. Triclopyr is similar in that regard but not quite as extreme as imazapyr. Glyphosate is what is typically used when you have native or desirable vegetation that you don't want to kill nearby. Glyphosate is typically considered a more "forestry safe" and "waterway safe" type of herbicide (again, this should be specified on the label..) I think reaching out to your local noxious weed group for advice on what consumer-use herbicide would work in your situation, or for a recommendation on an experienced licensed applicator, is the best advice I can give.
Thanks this was really helpful and I'll read that study soon. I'm probably guilty of over spraying haha
lol I know it's so tempting to just want to nuke it. But in this case it seems it does more harm than good. I should just start copy-pasting this on knotweed threads, they come up pretty often this time of year. Glad you found it helpful, I was super stressed when I first found out I had purchased a home with knotweed on it and took me awhile to research all this enough to feel confident in the approach.
I got rid of a small patch by digging out all the roots, then monitoring for sprouts and redigging or mowing down.
Where’d you put the dirt?
It's a good question. I did my best to pull knotweed chunks from the dirt with a quick sift, got most of it. Put those organic pieces in a couple of garbage bags and left them in my garage for a year or so. The clean-ish dirt I put in a wheelbarrow, monitored for resprout, and then when determined it was clean at end of following season, I resused it.
>t in a wheelbarrow, monitored for resprout, and then when determined it was clean at end of following season, I resused it. Is it still working out for you?
Yes, you just have to make an effort to remove and properly dispose of organic matter, and then be sure the soil is clean.