Japanese knotweed nightmare
August 30, 2008 10:36 AM   Subscribe

Japanese knotweed is extremely difficult to kill with herbicides such as round up and the like, does anyone have any other ideas or herbicides in mind? I have a commercial property that has a bad case of this stuff that I can't get control of. I have at least 1000 square feet of this invasive plant and it keeps spreading. I useually run over it with a skid steer loader and knock it down and crush it but it comes right back. Round up does not seem to do anything and I look ridiculous with a little spray bottle of Round Up up against a towering wall of this weed. Any help?
posted by CFMartin to Home & Garden (15 answers total) 3 users marked this as a favorite
You want to talk to your state's cooperative extension service. Here's a search for cooperative extension bamboo weed that will give you suggestions from other states.
posted by LobsterMitten at 10:53 AM on August 30, 2008

There is a pretty good paper on the subject here [pdf] from The Nature Conservancy site on knotweed. Mechanical control requires heavy vigilance, you need to cut as low as possible at least every couple of weeks between April and August. Even then eradication could take a couple years.

The most promising method of herbicide control appears to be direct stem injection.

Depending on the nature of your property goats are a good solution, they keep the plants cropped close with little attention.
posted by Mitheral at 11:07 AM on August 30, 2008

I was going to say goats, too. They eat anything, even poison ivy.
posted by beckish at 11:23 AM on August 30, 2008

If herbicides are an acceptable choice for you Transline, which is selective to broadleaf plants, may be an option. It will leave your grassed unaffected. Milestone may be an alternative choice.

Goats may work but they are far from selective. They will eat poison ivy or poison oak but only after the more palatable vegetation has been consumed.
posted by X4ster at 11:47 AM on August 30, 2008

As noted above you need to mow it constantly for that to be effective.

Probably the best thing to do is cut and remove it as much as possible then paint/ inject the stumps with an appropriate herbicide. Yo'll have to treat the regrowth a couple times to get rid of it all. Make sure you remove as much as possible and dispose of it somehwere it's not going to cause a new infestation.

There are places that rent goats/ sheep to control plants. They will come and set up a little fence around the area and put the goats on it for a few days and they'll eat it right down. Again, some retreatment will likely be needed.
posted by fshgrl at 1:03 PM on August 30, 2008

What about a propane torch weeder?

I've used boiling water to kill invasions like this.

If you just dig it up you should pay a kid to put it in garbage bags or burn it.

Why do you have to get rid of it? Is it ugly? Then why don't you put landscape fabric over it?

Salt may work (although I can't say I've had success with that myself). That is, if you don't want to grow anything there again.
posted by cda at 1:36 PM on August 30, 2008

one word:Garlon.......if you can find it
posted by patnok at 3:04 PM on August 30, 2008

goats first, but if you really want to go the herbicide way and it is 'commercial' property then you should contact your states dept. of agriculture and they can get you in touch with somebody who is licensed to use the good stuff, whatever that may be, but try the goats first.
posted by docmccoy at 4:38 PM on August 30, 2008

You can eat it...
posted by Matt Oneiros at 5:08 PM on August 30, 2008

Get some large tarps (I use 12 by 20), thick so they block light. I got mine at WalMart. Wire them together to go over mounds of plants. Make sure they are well staked, or run wire to stakes, so they don't blow away in high wind. Wait a couple of weeks. Blocks water and light. Keep the tarps as many invasives hunker down in the root system and sprout at the first opportunity.

Something has to be there to compete &/or suppress the plants. The spectrum is something like (garden .. landscape fabric .. concrete), and should support the end-use of the property.
posted by dragonsi55 at 5:43 AM on August 31, 2008

I've successfully killed quite a bit of this stuff in urban parks and my own backyard. Here's a somewhat proven technique:

1) throughout the early part of the growing season, knock down the plants as much as possible, maybe every 2-3 weeks. This can be done by hand with loppers or if the infestation is large enough, your skid steer. However, this species can spread from root fragments as short as as an inch--clean off your skid steer well or you may bring knotweed to other sites. This causes the plant to try to regrow as quickly as possible to reach following size and thus use up its stored energy reserves.

2) in July or August, a week or two before it flowers, cut it back to about 8 inches high, let it grow for two weeks as it really wants to flower so it will be pumping a lot of energy into growth and using up the stored energy in its roots. Then spray it with Roundup (I think a 4% solution), or better yet, Roundup and Garlon 4a. If your site is near a stream or wetland, use the wetland safe surfactant for the roundup.

3) The knotweed should die back pretty quickly, but in my experience two years of treatment are need to control it. Spot treatment may be needed for several more years to get the tough ones or sprouting seeds.

In my experience tarps will not work with this species, as it can grow and break through concrete.
Mulching heavily may help hold the soil on the site, but will not smother them either, it can grow through four feet of soil placed on top of it.
posted by buttercup at 7:23 AM on August 31, 2008 [1 favorite]

I am slightly ahead of you in this battle. I think buttercup may be onto something but I will just say what I do. In future I may merge my approach with buttercups.

First, are you in the UK? If yes there are regulations about how you dispose of JKW. In short, the best bet is to burn it on site. Moving it to an authorized disposal site is a nightmare. If you take it down the council dump they will try and knick you as spreading JKW is an offence.

Roundup will only work if it can get into the plant. Therefore you can only spray it on a plant in leaf.

My technique is

Year 1. First let it grow to about 4 foot put on plenty of leaf and then spray with round up every 4 weeks. Do not cut down. You will get mottling on the leaves.

At the end of summer 1 carefully cut near base and burn everything. If possible wear a decorator’s disposable boiler-suit and overshoes and burn them as well. You really can start another infestation with the tiniest bit. You really don’t want to bring it back into your own garden.

Year 2. It is already a weaker plant. It will throw up shoots again. This time go in with the round up at about 2 foot high and spray every four weeks. Again, don’t cut down until the end of the year and burn everything on site.

Year 3 mow, mow, and mow never let it show its face.

All JKW plants are female and thus identical. There is a chance that a biological/genetic method will be developed in the next few years as the market for it will be huge. Let's hope.
posted by priorpark17 at 7:04 AM on September 1, 2008

If you are spraying herbicides, a gas powered backpack sprayer will get the job done a lot faster than using one of those little spray bottles.

Depending on the laws where you live, there may be a wider range of herbicides available to a licensed applicator than to consumers.
posted by yohko at 10:24 AM on September 2, 2008

I have been experimenting with several different methods on the infestation in my yard (in Ottawa). The best success I've had to date are the clumps I let grow to full size, injected the stem below the 2nd node with roundup in July, and then removed them in August. Dead, dead, dead. Labour intensive, though, as you have to poke a hole in each stem (I used a sharp awl) and then inject the herbicide. And you can only use that method on clumps with larger stems (1 cm diameter seemed to be the smallest I could inject). There are commercially available injection systems though. Looks like it would be worth a try if you have a lot to get rid of.

Physical removal (digging) has not worked too well. Mowing has not been successful. Regular sprays of roundup havn't worked either. I'm still waiting to see on the clumps I sprayed with roundup in late August/early September (when the plant is drawing nutrients back down to the root clumps for winter), and then dug up all the big root clumps in October. Those root clumps were starting to ro and didn't look heathy, so I have some hope that may have been somewhat successful.
posted by fimbulvetr at 1:32 PM on January 23, 2009

Here is a PDF that explains the stem injection method I used
posted by fimbulvetr at 1:34 PM on January 23, 2009

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