Knotweed Eradication October 20, 2006 Well, I made it to the knotweed conference at Cornell University and I lived to tell the tale! I have more than a dozen pages of notes from the other presenters, much of it full of technical botanical jargon or intensely-focused genetics concepts. So much is being done by many in academia and by many in watershed management roles, it was hard to decide what to include in this email. This is the break-down of most of what I learned; please feel free to contact me with further questions! Native to the volcanic slopes of Mount Fuji, Japanese knotweed (Polygonum cuspidatum, Fallopia japonica, Mexican bamboo, donkey rhubarb) was brought to England in the early 1800’s as an ornamental plant. Its lovely sprays of tiny white blossoms enhance its exotic, bamboo-like appearance. Knotweed was an award-winning bit of vegetation, esteemed for its apparent ability to control erosion on stream banks. Once planted, however, knotweed escaped its confines by means of a rigorous root system, which gradually infested the countryside with amazing speed and ability. The plant invading the UK is one enormous clone of that original plant, ‘the biggest female in the world’; the infestation in Swansea alone has been estimated to weigh ‘the same as 40 blue whales’ in sheer biomass (leaves, stalks, roots). [www.cabi-bioscience.org/html/Japanese_knotweed_alliance.htm] This widespread infestation has occurred solely by means of cuttings or pieces of root (rhizome) that have been cultivated as garden plants, discarded as lawn waste, or inadvertently spread after roadside mowing or along stream banks after flood events. A piece of knotwood the size of a macaroni elbow can re-root, creating a whole new colony. There are many accounts of knotweed emerging inside people’s homes from outdoors, breaking through many inches of tarmac, obscuring road signs, crowding out native saplings, and damaging roads, airplane runways, dams and building foundations. The UK treats knotweed like a hazardous material, establishing and enforcing laws and regulations as to its movement, excavation and disposal. The first record of knotweed in the US is in New York City’s herbarium from 1870. This was a cultivated, planned introduction, possibly in conjunction with the influx of Japanese and Chinese immigrant workers; knotweed enjoyed popularity as an ornamental in this country for 120 years. It is currently reported in nearly every state, including Alaska but excluding Hawaii (which I find interesting, due to the high number of Japanese immigrants who traveled to Hawaii to work the sugar cane plantations). It is causing damage and has really made a negative impact on wetlands, river banks, salt marshes and even sand dues on Long Island. In Delaware, a large stand of knotweed has grown along a bridge abutment, sent its shoots down some twenty feet deep, through a two-foot-thick brick wall, and up through a slate sidewalk. Wow. If I hadn’t seen the photos, I would not have believed it! I first became interested in Japanese knotweed in 2003, when I began to see it around the Black River watershed. Now, I see it everywhere I look, and the problem can only become worse. While the plant in the UK is one large clone and spreads entirely by vegetative means (cuttings and pieces taking root in new places), our American knotweeds are reproducing vegetatively as well as by seed! There are many hybrids present in the US now, all of which are capable of reproducing. So, who cares? Isn’t this just nature’s next step in evolution, survival of the fittest? My belief is that this plant lives on the slopes of active volcanoes for a reason: it is supposed to be there. It only got to the UK and the US by artificial means; it belongs in Japan. Yet here it is, happy as can be, on our stream banks, along our roadsides, in our faces. We need to find out where it lives (our backyards, our rivers, our wetlands), and work cooperatively to eradicate it, and to replace it with native plants. That knotweed displaces native species is a no-brainer; it sprouts early and aggressively, shading out native plants that attempt to emerge later in the season. Its rhizomes, like most other plants, have an what’s called allelopathic quality ~ they secrete a chemical defense into the soil to inhibit the competitive growth of nearby plants, as well as to kill off potential pathogens (diseases, harmful fungi, etc). In winter, the tall jointed stalks die and bend over, becoming a brittle, dense mass that remains for at least two years. This mass prevents any hope of anything else growing underneath it in the spring. There is anecdotal evidence to show that knotweed does NOT prevent erosion; in fact, it seems much more likely to cause or exacerbate erosion problems. Its dense root system is more like a series of long fingers than the net- or web-like root systems of many native plants that line our stream banks. A web or net is far more suited to retaining soil than is a bare hand, fingers outstretched. Also, during winter months, there are no under-story plants growing beneath the dead stalks and foliage, so that soil is bare and susceptible to washing into streams and rivers during late autumn and early spring rains. Soil eroding into the river means increased turbidity, or sediment suspended in the water. This can harbor intestinal parasites such as Giardia and Cryptosporidium, which attach to suspended particles. During a high-water event, thick knotweed stalks can easily be washed downstream to collect in and clog waterways, creating a damming effect and adding to the flooding problem. While there have not been any formal studies yet to determine the extent to which knotweed impacts water quality, there is very strong anecdotal evidence that large stands (such as we see around the Black River watershed) can have serious negative effects on water quality and habitat. Knotweed forms dense canopies, but it does not arch over wider rivers. In fact, knotweed can starve out trees, which would serve to shade the water; the sun warms the water, which reduces the amount of dissolved oxygen the water can hold. River-bottom critters and fish need that oxygen to live. Also, trees along a riverbank provide ‘leaf litter’ (dead leaves on the ground and on the bottom of the river) in which little critters live, which feed larger critters, and so on. Research is currently under way to determine if the leaf litter of knotweed will be used by river-bottom critters in the same ways as native leaf litter. The riverbank trees also provide ‘woody debris’ when they die or lose branches; the limbs fall into the river, creating fabulous habitat for all sorts of creatures, and any fisherman worth his or her salt will tell you that dead logs in the water are terrific spots to cast for trout. When the amount or variety of river-bottom critters (benthic macroinvertebrates) is reduced in a river, fish no longer use that stretch of water for their habitat. With no place to hide, nothing to eat, and not enough oxygen to flourish, the fish will go elsewhere to live. A ripple-effect begins; with no fish to eat, other animals will depart the area, and our ability to go fishing with our kids and grandkids will be eliminated. The presence of Japanese knotweed on our stream banks impacts recreation (try bush-whacking your way through a stand of it while carrying a kayak, canoe or even a fishing rod, not to mention swimming in muddy water), aesthetics (how attractive those dead stalks are in the fall, winter and early spring), and even property values (just watch the annual fall and spring floods wash your backyard downstream). There are few creatures or plants present in knotweed on a regular basis, although some insects and reptiles seem to forage in the stands; there are reports of birds pecking holes in the stems to get at insect larvae inside, and I have personally seen a beaver lodge with knotweed in it. Insects do eat the leaves (such as Japanese beetles) and some lay eggs in the interior of the stalks, but deer and other large herbivores have not been observed grazing in knotweed stands. I’ve been told that pigs will chow down on the stuff, and that goats tend to like it as well. Eating too much of it can give humans diarrhea, but its leaves have traditionally held medicinal powers, which is probably another reason it was brought to other countries from Japan. The knotweed in Japan is held in check by various native 'controls.' Fungus and native predatory herbivores eat the leaves, stems and roots of the plant. Each of these 'biocontrols' is being examined as a potential weapon against the knotweed invasion here in the US. The ultimate focus of the Japanese knotweed conference at Cornell University last week was to brainstorm and network on control methods. Many folks discussed (at great length) the proper and most effective use of herbicides; the presentations on biocontrols were fascinating, but the reality of introducing one in North America is potentially ten years away. Research on this has been going on for years, in a joint effort between scientists in the US, the UK and Japan. The process for getting a biocontrol agent approved in this country is painstaking, and can take a decade or more from start to finish. The last thing we want to do is to release an insect or fungus on the knotweed, and find ourselves with an even worse invasive species than the knotweed! Much is being explored state-side, including research into the allelopathic chemicals produced by knotweed ~ can it be used to create a deadly, species-specific herbicide? Still working on that fascinating possibility. All manner of cut & cover methods are being explored for best possible outcome and efficiency ~ the overall consensus is that if you have knotweed on your property, you can manage it, but you are in ‘for the long haul’. You can expect to cut and CAREFULLY dispose of knotweed material for a good three years. If you find yourself cutting the stuff down, please do NOT simply compost or dump the cut material!!!! It will simply resprout, compounding your infestation exponentially. It can be left in plastic garbage bags until either dried or liquefied and absolutely dead, then brought to a landfill. If you’re going to cut, do it in the spring when it’s about a foot high (cut it down to the first joint in the stem), then again every two or three weeks until the fall ~ do a final cut BEFORE IT FLOWERS. Each plant can produce hundreds of thousands of viable seeds! Removal by hand-pulling is a losing battle, at best. Even a tiny piece of rhizome left in the soil can resprout. You’ll need to either make sure you get every last bit of plant material out, which may work if you have a small stand, or do methodical cutting. Pulling the roots out generally creates more work for you for years to come, and excavating the area (rhizomes can go 9 feet or more deep, and 60 feet laterally through the soil) leaves you with a huge hole in the ground, into which lots of other hardy invasive plants would likely move before you know it: multiflora rose, barberry, mile-a-minute vine, burning bush, you name it! Plant material may travel to new locations by means of roadside mowing, or by transport of quarry stone and excavated fill from construction sites. These are all areas being addressed; if you are removing or receiving fill of any kind, make sure it is knotweed-free, to avoid giving plant material a free ride to a new home. One of the most important points made in the conference was that knotweed (or any invasive, for that matter) cannot be managed in a bubble; the entire watershed and overall ecosystem must be taken into account when working to eradicate one species. The follow-up plan for knotweed removal must be in place before tackling such a project. In this case, the planting of native species is a cornerstone to rehabilitating the habitat affected by knotweed. We must roll up our sleeves and work together to manage this invasion; a gentleman from the North Carolina office of the EPA described Japanese knotweed infestation as a “slow ecological train wreck.” We are not powerless to avert it, we just need to get informed, get together, and get busy. Stay tuned for updates on some projects to do just that in the coming months! There are folks at the local level and at the watershed level who are busily developing plans to tackle this issue with a hands-on, practical approach that will rely heavily on partnerships with landowners. Thank you for your patience reading this email, and for your support for my attendance at this fabulous conference. Please let me know if you’d like any further information from the conference, and if you’d like to be part of upcoming knotweed management projects. Cheers, Kelly Stettner |
