Help! Knotweed knightmare of a different sort...

13 years ago

I have a potentially serious Japanese knotweed problem spread over almost 3/4 acre. It involves thousands of these invasive weeds. However, it's a bit different from most of the situations I have been able to research, and am hoping that someone has experience with a similar situation.

I've been working on my future retirement property every weekend for the last couple years; it's 3 hours away from my current house. House construction was last winter and rough landscaping this spring. On May 15 I finished spreading loam and grass seed over 3/4 of an acre. The lawn is coming up great, and so is something else. It turns out that the last 16 yards of loam contained a LOT of someone's knotweed root clippings. They are generally 1 to 4 inches in length, and typically 1/4 - 3/8 inch in diameter. They are in the top 3 inches of the soil and are sending out 1 to 3 small stems and leaves each. On close inspection I don't think these pieces have sent out many rhizomes yet. They are distributed randomly throughout the lawn, , and every week there is a stem coming up about every 5 square feet or so. I have dug up many hundreds of these so far, but there are more on the way, and the grass is almost ready for its first mowing.

Almost everything I have read about so far has dealt with attempts to eradicate mature and established knotweed growth, typically in a patch, and not with newly sprouting sprigs from widely distributed root pieces interspersed in a large lawn. Those treatments also tend to advise on eradication of large plants around the time that they flower, and typically involve glyphosate application at that time.

So, what should I do in my situation? I could wait it out til August and "hope" %^) that the knotweed grows really tall and flowers so that I can hit it with a herbicide....but this seems extremely risky, especially given the sheer number of pieces in the soil and fact that it's been detected early. Plus, the new lawn needs to be mowed, so leaving it alone doesn't seem like a very practical option.

Oh, and to the person who left their clippings in my loam... not a particularly wise thing to do.

Thanks - andy

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Comments (7)

noinwi
13 years ago
This info for your area suggests constant mowing to weaken the rhizomes. I don't know if using a broadleaf weed killer would work since I think JK is a grass, but if you can weaken the rhizomes, maybe you can over time 'paint' glyphosate on the remaining emerging JK leaves so it will translocate to the rhizomes, and leave your lawn intact. You don't want to let it flower, but put out enough leaves for the herbicide to do it's work. Fall seems top be a good time to do this. Sorry you got someone else's headache...it's going to take time to get rid of it. HTH

Here is a link that might be useful: invasive weeds of Maine
jean001
13 years ago
Call everyone you know. Promise them beer and pizza. And have a work party. Now!

Also contact your regional Soil Conservation Service which is likely to help or, at the last, to advise.
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Thanks for all the responses, folks! Actually, I want to start another thread of most hated and best liked weeds. Jackie, I'm tempted to take issue with that word 'perfectionism'. To me the absolutely manicured garden suggests not a desire for beauty, but a desire for control. As you point out, allowing Nature to become a collaborator in one's garden design can bring lovely results, and to me what is most lovely is most perfect. Maniacally maintained gardens aren't necessarily the most beautiful ones around. I am a perfectionist in my own way, meaning that I always try to create the most beautiful garden I can, even if I almost invariably fail. All of which opens the way to a discussion of different ideas of beauty. Lori, you do list some ugly weeds. About the lawn: with our dry summers and for various considerations, I've never tried to have a lawn and never watered what grass struggled into existence. (Italians, by the way, go mad for what they call 'English lawns', a smooth close-clipped expanse of emerald green maintained at huge expense of water, fertilizer, and poison.) Perversely enough, we are coming to have a lawn. We've always had annual grasses that make a good show in spring and then die during the summer drought; but there's a perennial native grass that makes quite a decent lawn grass that has been expanding its territory, so that in time I think we'll actually have a permanent grass covering. Moral of the story is, I think, that you need to find adapted grass species for your lawn, that can handle periods of drought. Also, do you dislike non-grass species in your lawn? I've always enjoyed clover and English daisies and so on in my grass (I even rather like dandelions, but I know that's extreme); could you bring yourself to like them? As you point out, having something--ANYTHING--growing brings advantages with it. Some perennial grass species do go brown in periods of drought but without dying; could you live with that? Here in the summer for green I rely on the wisteria pergola, on the trees and shrubs and on the potted plants, but not on the grass. Hoovb, nice work if you can get it!! I have the highest opinion of thick blankets of mulch. However, we have a very large garden; it's too steep for anything but a tractor to get in--wheelbarrows are really difficult; I have no convenient source of mulch. For all these reasons I began to ask myself why on earth I was pulling annual grasses out of the beds, since they are simply Nature's mulch, grown in place and at no cost to myself. Certainly I mulch all I can, but the self-sown wild herbaceous plants help. Suzy, I hate mallows too, but fortunately they're not one of my major problem plants. I do pull them wherever I find them. Your comments about butterflies made me wonder about our bee and butterfly population this summer. It seems to me we haven't had many honeybees at all, and, now that you bring them up, I haven't seen many butterflies either--fewer than in other years. Note that we use no pesticides, and I doubt our farmer neighbors do either, as they grow crops for cattle feed; and we're otherwise surrounded by woods. The wasp and bumblebee populations appear healthy enough. Melissa
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Sounds like some sort of knotweed, Polygonum species (although taxonomically confusing....also includes Persicaria, Fallopia and a few others). Many of these are rampantly rhizomatous and/or invasive. Some of the very weedy ones tend to form long hollow stems and have leaf growth clustered at the top of the stems. And can also produce large oval, almost heart-shaped leaves. They grow in colonies, much like bamboo, and are even referred to by the common name of Mexican bamboo (who knows why - not Mexican and not a bamboo!). With very few exceptions, not something I'd recommend planting intentionally :-)
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Okay, I will go that route, I have been doing small scale removal at that site by hand and I think the Park service is doing some sort of woodland restoration. Right now I got a lovely back yard woodland garden of Wild Ginger, yellow Trillium, Jack in the pulpit,Wood poppy, wild clombine, bishops cap and solomans seal. I'm trying leaf litter in there now to help establish new plants.
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We are kindred gardening spirits, Melissa! I welcome all kinds of volunteers in the garden--native and other "weeds" as well as neighbors' contributions via breezy days. I find that beneficial insects appreciate the volunteers, too. Volunteer fireweed blew in prior to the near mcmansioning of the Victorian home/lot across the street. Bees, butterflies, hummingbirds and I adore the lavender pink blooms in high summer. I occasionally rip out potions of clover and oxalis plants. The rest is hopelessly interwoven with the garden, but everyone plays well as long as I keep the creeping beauties knocked back a bit. Dandelions are healthy food and my daughter loves to blow the seeds. I'll be scraping away the final chunks of sod this summer in order to lay a small back patio area, so no worries about dandelions in the lawn. Borage comes and goes with the wind. My husband "rescues" all kinds of plants and brings them to me for rehoming. It's fun to pick and choose and pass along. Birds have delivered various annuals to my beds, including sunflowers. I stay on top of unwanted woody sproutlings, like the gazillion holly plants invading every area of my yard. Birds and berries and an ongoing removal exercise. Bindweed has to go as do Himalayan blackberries. My favorite unexpected discovery is scarlet pimpernel which opens and closes its blooms with weather changes. A sweet, delicate coral-flowered groundcover meteorologist. Great fun! Carol
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Kimmsr
13 years ago
For many people the terms "loam" and "topsoil" are interchangeable when they should not be. Loam is a soil type, generally about 25 percent clay, 25 percent silt, 45 percent sand, and about 5 percent organic matter while "topsoil" is whatever was scraped off the top 4 to 6 inches of someplace, sometimes with organic matter added to make it look good.
That you have Knotweed in that soil indicates the soil was simply scraped off someplace where Knotweed grows and getting rid of it is difficult. Anytime you see bits and pieces of root remove them and whenever you see even a bit of plant starting to grow remove that.
green17
13 years ago
First of all absolutely DO NOT let this plant grow tall and flower and have time to send its rhizomes to the center of the earth. With new shoots use Ortho Total Kill Lawn Weed Killer. It kills knotweed and many other weeds but does not kill your lawn. I've used it for the same purpose and it really works great. It actually lists knotweed in the list of weeds it kills. Wait until new shoots grow to about 3 or so inches tall with some leaf growth and then spray. The next day you will already see the knotweeed browning and curling over in its sure death. Also, be careful Ortho Total Kill comes in two varieties one that is safe for lawns and one that isnt. Look at Home Depot for the green bottle, not the blue one, if you do not want to kill your lawn. Also I would suggest buying the 32 oz. concentrate and making your own mix. Mix a tiny bit heavier to really feel the satisfaction of knocking this plant back to Japan from where it first came. Bye bye knotweed.
petchie
13 years ago
Battling the same issue here. It is not in the top 3 inches though, it is in the yards and yards of new fill put in behind a retaining wall to create a side yard.

I have been injecting some of them, and using a dandelion puller on some. Should I not be pulling and just cutting? It goes down really far, so digging it out will be hopeless.

Should I just let the shoots get 3 inches tall and spray? inject? paint? with full strength Roundup Concentrate? Or should I use the weed b gone max?
awl51
Original Author
13 years ago
petchie - sorry to hear you are in the same boat as me.

I've been holding steady for the past few weeks with my knotweed problem. I'm still pulling out root clippings that have sent out shoots, although that's become harder to do each week. Mowing and bagging is next, with the grass clippings quarantined. Whatever is left after that I'll paint with herbicide in the fall, when it's most effective.

Besides some advice in this forum, I found some good information resources. For example:
http://www.glifwc.org/invasives/Fallopia_spp/control.html
http://www.co.clark.wa.us/weed/documents/2005-crockett.pdf
http://www.uri.edu/cels/ceoc/documents/japaneseKnotweed.pdf (the references at the end of this one are particularly good, I think)

In the end, it seems like herbicide cocktails directly applied (painted or injected) have a pretty good chance of success. However, it may still be a multiple-year process.

Good luck.

-Andy
HU-546663088
3 years ago
You had better get to it quick smart, that stuff grows deep and spreads like wildfire. My neighbour planted it knowing what it was, and I have been battlng it for years. I complained to the City of Waterloo, they said because the neighbour knew what it was there was nothing that they would do. I have used Knock Out sucessfully but needs several treatments, the treatments must get back to the original plant to kill it properly. Let me know how you manage the problem

Paul

Help! Knotweed knightmare of a different sort...

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Help! Knotweed knightmare of a different sort...

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