Knotweed overtaking UD habitat


The Upper Delaware River Valley is being invaded. Rapidly. Japanese knotweed is propagating on the islands and shorelines of the Upper Delaware.

A native species of Eastern Asia, Japanese knotweed was introduced in England in 1825 and then brought to North America in the late 1800s. Imported to Philadelphia for the 1876 Centennial Exhibition, this invasive species is now found in 38 states. The infestation is greatest on the eastern seaboard because the plant was introduced in Philadelphia. And it’s been spreading rapidly through the Upper Delaware for the last 15 years.

Jamie Myers is a biologist for the Upper Delaware Scenic and Recreational River. One of her responsibilities is to try to control the plant from further impacting the river’s habitat and ecology.

Japanese knotweed is a big threat to the Upper Delaware because it takes over the banks of the Delaware’s tributaries and the main stem. Though the root system can be quite expansive, it does little to stabilize banks or prevent erosion and sedimentation.

“With the recent flooding, people have accurately documented that the amount of erosion around the knotweed rhizomes (or root structure) is much greater than where the native grasses are,” Myers said.

But that’s not all the Japanese knotweed disturbs.

Many native plants, shrubs and trees help to keep stream banks stable, which reduces erosion, and their leafy branches shade streams, keeping them cool enough for local fish species, including trout. Japanese knotweed does not. With the banks destabilized due to excessive Japanese knotweed growth, the river gets impacted with more sediment that in turn affects the aquatic insects, which can impact the fish that feed on them.

Japanese knotweed stands also create limited habitat for birds and small mammals. Animals have a difficult time walking through it and since it is not a native plant, it is an extremely limiting food source. Japanese knotweed replaces native food sources depended on by wildlife and reduces or sometimes eliminates host plants for native insects and birds.

Japanese knotweed is extremely difficult to control and extremely easy to spread. In fact, without education, a well-meaning homeowner can easily help spread the plant.

To that end, Myers and the Delaware River Invasive Plant Partnership (DRIPP)–a group of individuals from 40 federal, state and local organizations, who work to advance regional coordination and planning for invasive plant management throughout the Delaware River watershed—have turned their attention to preventing the further spread of Japanese knotweed along the Upper Delaware River. Thus, last winter the informal group known as the Japanese Knotweed Initiative (JKI) was formed. The initiative has three focus areas, including education and outreach, science and planning.

Many public and private organizations including the JKI are working to address the spread of knotweed in our region and to evaluate environmentally sound control measures. The science focus group of the JKI realizes that science is continually advancing and that there are still many unanswered questions when it comes to Japanese knotweed control.

The education and outreach focus group was successful in developing a brochure called “Spread the Word Not the Weed.” Through a grant from the Northeast Region Exotic Plant Management Team, a federally funded National Park Service program, a short movie infomercial was produced and is being shown as part of the previews at the Callicoon Movie Theater in Callicoon, the Capra Cinema in Hancock and the outdoor summer cinepark series in Livingston Manor.

Four community demonstration sites are tackling knotweed locally. At the demonstration sites, volunteers, using scientifically supported guidelines developed by the JKI, are implementing and documenting a variety of techniques to control and hopefully eliminate Japanese knotweed stands in their local communities. Representatives of the JKI have worked together to review scientific literature and field manuals, meet with expert practitioners and develop guidelines that are the most appropriate for these sites at this time. The JKI hopes to begin basic monitoring of success across all four sites to improve the knowledge of knotweed in the Upper Delaware basin and to support future projects.

The Livingston Manor High School Environmental Science class began the effort with a demonstration site at Renaissance Park in Livingston Manor at the confluence of the Willowemoc, the Little Beaverkill and the Beaverkill as a hands-on educational experience. The Beamoc Chapter of Trout Unlimited will continue the work throughout the 2005 season.

The Callicoon Creek Park Committee is running the project at the park in Callicoon on the banks of the Callicoon Creek. The Delaware River Foundation is leading a demonstration project in Hancock with workdays at Junction Pool fishing access on the main stem of the Delaware River every Saturday morning. And in Delhi, an Americorps group, Catskill Outdoor Education Corps, which is supported by the Delaware County Soil and Water Conservation District and New York City DEP, is running a demonstration project at Kingston Street Park along the West Branch of the Delaware River.

“These are all great partnerships between the community, the school, DRIPP and the National Park Service,” Myers said.

At each site, displays explain the steps being taken to eradicate and slow down the spread of Japanese knotweed. The new JKI educational brochure is also available at each demonstration site.

“It’s important for people to learn to identify the plant, and learn specifically what not to do when dealing with this plant on your own property,” Myers said.

The National Park Service (NPS) is currently not advocating the widespread use of herbicide application to control Japanese knotweed infestations. Until science advances enough to answer some important research questions, including identifying both the positive and negative effects of treating Japanese knotweed on native terrestrial and aquatic species and communities, the NPS feels that one of the best strategies is to be educated about the plant and to stop the further spread of the plant when it is within your control.

A biological control for Japanese knotweed is currently on the horizon as well. Researchers at Cornell University are working to establish biological control techniques and anticipate the release of a Japanese knotweed biocontrol within the next five to seven years.

“We had a regional symposium on knotweed in Kingston, NY and participants from the west coast were amazed at how terrible the infestation is on the Delaware River,” Myers said. “In relation to the rest of the country, I was surprised myself.”

Knotweed control: Top ten tips

1. KNOW HOW IT SPREADS. Japanese and giant knotweed is spread primarily by the growth and fragmentation of rhizomes buried in the soil or even stem fragments. Very small fragments of rhizome and fresh stem material are able to produce viable shoots and roots within as little as six days. Seeds, which are dispersed by wind and water, are a less aggressive but still significant form of propogation.

2. DON’T DIG. Do not try to dig up the rhizomes. It is nearly impossible to be sure you’ve gotten all fragments. Rhizomes can also be very large—as much as 60 feet in length. The digging required to completely remove all fragments of rhizome would cause such disturbance and potential erosion that it would only encourage sprouting of remaining fragments.

3. REPLANT WITH NATIVE PLANTS. It is important to rapidly establish native or non-invasive plants to control knotweed and stabilize the soil. Knotweed seedlings do not compete well with other vegetation. Consult your neighbors, local nurseries, garden clubs or the Internet for suggested plantings.

4. CUT REPEATEDLY. Repeated cutting of the stems reduces vigor and can eventually reduce the root reserves in some cases, particularly with small, isolated populations. Cutting is effective only when done repeatedly as it will result in new shoot emergence. At least three cuts are needed in one growing season to offset rhizome production. Repeated cuttings must be continued until knotweed stops re-sprouting and must be checked regularly for any regrowth. Dispose carefully of all cut stem fragments. If cut stems cannot be burnt, seal them in plastic bags or spread and dry them in the sun, away from water or exposed soil.

5. COVER AND SHADE. Some success has been noted with cutting combined with shading. After cutting near the soil surface, stands can be covered with sheets of plastic. There is some early evidence that clear plastic has greater results due to the sun baking the rhizomes. Be very careful to secure the plastic, particularly near streams and rivers, so that it cannot be washed or blown away.

6. DECIDE ON HERBICIDE. We do not currently recommend the use of herbicide along the banks of the Upper Delaware River due to potential risks to rare and endangered native fish and mussel populations. If you do use it, read the labels carefully and take great caution when working near water (painting or injecting cut stalks instead of spraying). Currently the most effective means for controlling large stands of knotweed is a combination of cutting and spraying with an herbicide containing glyphosate, a non-selective herbicide that will kill all vegetation, so it is important not to let spray contact any native or desirable vegetation. Cut stalks in early June to draw reserves out of rhizome. In August or when stalks reach approximately four feet tall, spray to coat leaves but not so heavily that herbicide drips off the leaves. Check regularly for any regrowth or reinfestation and spot treat.

7. AVOID EXPERIMENTING WITH HOUSEHOLD SOLUTIONS. Herbicides are not the only substance that can damage soil and kill native vegetation and wildlife. Seemingly harmless applications of vinegar, bleach or other household products can be even more damaging to the environment than herbicide.

8. NATURAL CONTROLS. Studies are currently being conducted on biological controls (fungal agents or herbivorous insects that control the plant in its native habitat), but it will be several years before we know how safe and effective they may prove. To learn more, visit BIOSCIENCE/japanese_knotweed alliance.htm.

9. KEEP LEARNING AND TEACHING. It’s important to continue to search for and share information regarding the control of knotweed. New studies are being published all the time, and much like human health, the more we learn, the more treatment options we have. It is often combinations of recommended control methods that work best. Your property has its own, unique qualities that either enhance or detract from the growth of knotweed.

10. AVOID PLANTING IT. Knotweed is still sold and exchanged for ornamental use. If you live in an area where knotweed is a problem, avoid introducing any varieties. Names to look for include: Japanese knotweed (Polygonum cuspidatum, Fallopia japonica or Reynoutria japonica), Giant knotweed (Polygonum sachalinensis), Japanese or Mexican bamboo, fleece flower, fallopia, lace plant, and Sally/donkey/gypsy/wild rhubarb.

This tip sheet was prepared by the Delaware River Invasive Plant Partnership for a workshop in the Upper Delaware River region of NY and PA.

For more information call 570/643-7922, ext. 12 or email jstennhart@tnc.orgfor.

TRR photo by Tom Kane
Japanese knotweed is taking over Upper Delaware habitat (Click for larger version)