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Knotweed buds, early spring

Photo credit: Jeff Parsons

Knotweed shoots, spring

Photo credit: MRBA

Flowering knotweed, fall

Photo credit: Jeff Parsons

Knotweed stalks, late fall

Photo credit: MRBA

KNOCKOUT KNOTWEED

Wanted:  Orleans County landowners with knotweed on their property.   For more information on how we can help, please reach out.  Email us.

Over the past three years, MRBA has been battling the incredibly pervasive invasive, Japanese knotweed.

Knotweed is an invasive species that was introduced from eastern Asia to the United States in the 19th century. This rapid-spreading and dense vegetation shades out native plants, and its shallow root system creates large areas vulnerable to streambank erosion. Additionally, knotweed can reproduce and spread from even small fragments of the plant, which makes removal and treatment difficult.

The Knockout Knotweed project strives to identify effective

non-chemical treatment methods to prevent and combat  knotweed invasions, with the goal of providing ways local landowners and residents can treat knotweed patches on their property. As we progress with this project, we will include updates to our findings on our website and encourage you to join us at our annual Knockout Knotweed Bonfire in the late fall.

 

Check out our events page for our most up to date details on upcoming events by clicking below.

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Plot of knotweed at Riverwalk Park in Montgomery

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Knotweed invasion on embankment along

Missisquoi River in East Berkshire

Flowering knotweed at Riverwalk Park 

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Unstable bank with knotweed stalks along the Missisquoi River in Troy

Knotweed leaves at our pond liner testing plot at Riverwalk Park

JAPANESE KNOTWEED: WHAT IS IT AND WHY IS IT A PROBLEM?

Japanese knotweed is an invasive species that is commonly found along river banks and along disturbed land like road sides or old agricultural fields. Japanese knotweed can be found in 42 of the 50 U.S States, and covers miles of river front property in Vermont, throughout the Missisquoi River Basin and beyond.

 

Knotweed can eventually suffocate native species, in part due to its ability to rapidly grow and shade out large areas. Knotweed has shallow roots which lead to river bank destabilization because of the lack of support from native vegetation and trees that were once there. During large rain events, the weakened river banks often break down and fall into the river, causing sediment to flow downstream, through our rivers, into Lake Champlain. Knotweed is incredibly resilient and eradication requires multiple years of treatment to remove, even when treating with herbicide. Overall, knotweed decreases water quality of our rivers and is an increasing issue of concern within our river basin. 

HOW TO IDENTIFY JAPANESE KNOTWEED

Knotweed is a hollow herbaceous plant that can grow up to 13+ feet tall at the peak of its growing season during the summer months. The stems are mostly green during the growing season, and turn reddish dark brown in the winter months. Knotweed has oval shaped leaves that end in a pointed tip. While emerging in the spring, Japanese knotweed resembles thick shoots like asparagus. As the knotweed continues to grow, it begins to resemble bamboo. In the late summer and early fall, knotweed will bloom with white flowers along the stem of the plant. During the late fall, - usually after the first few frosts -  the knotweed plant tends to "die back" for the winter and the leaves will fall off. 

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Knotweed stalks in the early spring

Knotweed stalks in the late fall.

WHERE IN OUR REGION IS THERE JAPANESE KNOTWEED?

In 2020, Arrowhead Environmental was contracted to map the knotweed within our region. On the left is an interactive map of the knotweed found during that summer survey. Red circles refer to knotweed found on the right bank, and green circles are knotweed on the left bank.

This map allows us to explore the prevalence of knotweed in our area, as well as areas that we can still protect through proper management strategies. 

WHAT IS THE KNOCKOUT KNOTWEED PROJECT?

During the past three summers, the Missisquoi River Basin Association conducted experiments to assess various ways to control this invasive species through mechanical means of smothering, cutting, and wire mesh to choke the plant. The inaugural year experiments occurred at three different locations around our watershed: behind the MRBA office in East Berkshire, downstream of Big Falls in Troy, and at Riverwalk Park in Montgomery. For the second and third summer, we focused on our more successful Troy and Montgomery plots.

Initially, five 8'x10' treatment plots and a sixth plot, used as a control comparison, were laid out at each location. MRBA staff collected data weekly at the three locations, taking photos for a time-lapse comparison, weights, and stem counts, and thereby monitoring the level of knotweed growth for each of the methods of treatment.

 

During year one, we used five treatment methods:

smothering knotweed with pond liner, smothering with cardboard and woodchips, covering with a metal mesh, cutting weekly, and cutting monthly.

 

As we refined our project for 2022, we determined that the three most successful methods have been: smothering with pond liner, cover with metal mesh, and cutting monthly (no significant difference was found between monthly and weekly cutting). These three mechanical methods have so far proven to be the most effective combat techniques with the least amount of maintenance labor required. 

We used the knowledge gained from the 2021 and 2022 field seasons during 2023 to continue seeking and refining the most cost- and labor-effective method of non-chemical removal of Japanese Knotweed. Due to the unexpected flooding impacts, MRBA staff have decided to delay native plantings until later into 2024. When we feel we have learned what we can, and begin to close out the treatment plots, we will plant native vegetation over the previously infested Japanese knotweed area, and will continue to monitor them. .

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Map of the layout of our 2021 Riverwalk Park site in Montgomery. 

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MRBA Staff preparing experiment plots in 2021.

All 2021 collected, bagged, and weighed knotweed before proper disposal during our 2021 Knockout Knotweed Bonfire Event.

WHAT ARE THE OUR TREATMENT PLOTS AND METHODS?

Control Plot

Control plots were left untouched during the field seasons, and only cut at the end of the growing season. After cutting, we measured the overall fresh weight. These control plot weights can then be compared to the cumulative weights of the other treatment plots, to help determine the effectiveness of each treatment type. 

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Control plot at Riverwalk Park at week 1 of 2021 experiment

Control plot at Riverwalk Park at week 1 of 2022 experiment

Metal Mesh Method:

1/2 inch hardware cloth was staked down over a knotweed patch 5-10 cm above the ground, crushing any stems present. The idea of this method is that Japanese knotweed stems would then grow through the grid eventually getting large enough causing the stems to girdle or choke themselves in the mesh, killing the stem. The continually growth would eventually weaken the rhizome structure cause then death of the plant. In practice, this method has been met with mixed results. Some plots have shown girdling of the stems, however, they still appear to sometimes continue to grow regardless of the breakage of stem. We plan to continue using this method for the next field season to monitor the success. 

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Example of a girdled stalk found at Riverwalk Park in 2021.

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Metal mesh plot at Riverwalk Park in August 2022

Smother Methods:

Woodchips and Cardboard

A thick layer of cardboard was laid down over a knotweed patch (crushing any stems present), and a 4-inch thick layer of wood chips was layered on top of this. During our summer experiment, we found this method to not work well as shoots were easily able to sprout up as early as two weeks after smothering at one site.

We will not continue using this method after 2021. 

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Woodchip plot in North Troy with a shoot appearing on week 2, 2021.

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Woodchip plot in North Troy with a multiple new shoots appearing on week 4 2021.

Pond Liner

At a second smother plot thick (45mil) pond liner was staked over a knotweed patch, crushing any stems present. We did not see any shoots make it through any of the pond liner on any of our plots, however, there still was growth of shoots underneath the plastic layer as well as on the sides. We plan to continue to use this method and leave the liner covered over the plots for as long as we are able to see how many seasons it takes for plant death to occur. 

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Pond liner plot at North Troy during week 1, 2021.

Pond liner plot in North Troy in August 2022.

Cutting Methods:

Weekly

We cut all stems within one plot down to the ground weekly, weighing the cuttings each week. This method was very labor intensive, especially in the earlier months of the year before the plant began to dieback. By the end of the season, there was little growth within the plot. We recommend to try this method if you have the labor, time, and a small enough plot to manage. However, we found no significant difference between cutting monthly and weekly, so have not continued this more labor-intensive method for our treatment experiments, focusing instead on the cutting monthly method.

We will not continue using this method after 2021. 

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Cut weekly plot at Riverwalk Park at week 1, 2021.

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Cut weekly plot at the MRBA office location at week 2. 2021

Monthly

Instead of weekly cutting, we also had a plot that was strictly cut once a month. This method was much less labor intensive than the weekly cutting, and seemed to have similar results. We also recommend this method if you have a small enough plot and are willing to put in the manual effort to maintain monthly. 

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Cut monthly plot at Riverwalk Park location in June, 2021

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Cut monthly plot at Riverwalk Park in August 2022.

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MRBA Project Manager, Ellen Fox, cutting knotweed at our East Berkshire treatment site in 2021 using our onion bags as storage

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Knotweed drying in our old office space in. Each collection bag was labels when it was collected and left to dry until our first Knockout Knotweed Bonfire in 2021

HOW TO DISPOSE OF JAPANESE KNOTWEED

Under Vermont law, it is illegal to dispose of Japanese knotweed by throwing any plant material in the trash or to take knotweed to the dump. Proper disposal technique is to contain the knotweed in a place where it can fully dry, but cannot blow away. Leave the knotweed to dry for a minimum of a month, though larger root balls may require multiple months of drying. Rhizomes of the plant (white under soil structures) are the most dangerous part of the plant for spreading. Ensure they are dried completely before disposal, which may take multiple months. Completely dried knotweed can be disposed of like any compostable material - or can be burned in a controlled setting: a fun way to celebrate the end of a summer battle!

When we originally began our project, we stored knotweed cuttings in onion bags and hung them up to dry. This method would be useful for smaller cuttings of knotweed, but proved to be cumbersome for collecting large amounts of knotweed (such as when we collect the end of the year's knotweed experiment plots). In 2023, we changed up our drying method and upgraded using pallets, a staple gun, a tarp, landscaping fabric, and MRBA staff muscle power to construct a drying box This method has greatly improved our drying processes, and 

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Our 2023 Knotweed Collection Box built by MRBA staff behind our office space. These pictures were taken in November 2023, and the knotweed had begun to decompose!

by the end the 2023 knotweed collecting, the knotweed had begun to compost - the ultimate win in our opinion!

 

The main goal of this new drying method was to allow the cut plant parts to air out to lower the risk of molding, and to ensure that plant parts are not spread by having a breathable structure (pallets with landscape fabric to decrease risk of plant material spreading). We will continue this drying process during our 2024 knotweed collection and track how this method composts.

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2021 Knockout Knotweed Bonfire 

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2022 Knockout Knotweed Bonfire 

Although we encourage composting as the preferred disposal method for knotweed, it is also still possible to burn completely dried knotweed in a controlled setting. To celebrate the end of each knotweed collection season, and to spread our knowledge about knotweed, the MRBA hosts an annual Knockout Knotweed Bonfire in the late fall at one of our experiment plots at Riverwalk Park in Montgomery, VT. Learn more about our efforts to control, manage, and prevent knotweed invasions, as well as learn how to properly dispose of knotweed with our disposal of collected knotweed. Snacks, fire, and good company are provided. Thank you to those who joined us in 2023, and we look forward to another in the fall of 2024! Join our mailing list to be notified of the next one!

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2023 Knockout Knotweed Bonfire 

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2023 LESSONS LEARNED

During the summer of 2022, MRBA Staff with the assistance of our 2022 LEAP Interns did a test planting at a site near our office in East Berkshire. This planting was used as a soft launch into native plantings, and something that we had planned to continue at our other treatment sites at the end of 2023. MRBA Staff have continually visited this plot, tracking changes and which plants survived - with a pleasant surprise of a black walnut sapling prevailing through the harsh 2022-2023 winter! Yet once again, with the Vermont flooding during July 2023, we were reminded why the knotweed battle is ever changing. The Missisquoi River region fared well in comparison to other Vermont communities, however, we are keenly aware that the knotweed was spread during this flooding. Flood waters carried not only knotweed greatly downstream, but it also took loads of sediment from eroding banks. Many of our monitored knotweed plots were greatly disturbed through the July flooding, and have since delayed our native plantings until 2024. And although this was a set-back, we are still up for the challenge and plan to continue our treatments through the 2024 Summer Season. This year's flooding has proven once again that knotweed has real impact to our waterways and will be a persistent water quality issue. 

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Our 2022 MRBA LEAP Interns and MRBA Project Manager planting native vegetation along a knotweed plot in East Berkshire for a trial planting.

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MRBA Executive Director Lindsey Wight and Project Manager Ellen Fox inspecting survival in spring 2023.

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A black walnut survived through the 2022-2023 winter!

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2022 East Berkshire pre-planting 

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 2023 July Flooding on 7/10/23 

CONCLUSION

Our overall conclusion from these past three summers of knotweed management is that Japanese Knotweed is in incredibly persuasive and tough plant that requires 

intensive removal efforts. The invasion of knotweed on our riverbanks is a continual problem that we will see the long-term effects of for years to come as climate change factors continue to worsen for our planet. We are continuing our project into next year to further our knowledge of this intrusive and difficult invasive plant. 

At the end of each experiment year, we summarize our findings and share them during our knotweed bonfire in November. Below are downloads for our first year (2021), second year (2022), and third year (2023) summary sheets. Reach out to our Field Coordinator, Sarah, for any burning knotweed questions!

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Did you know that you can EAT Japanese knotweed? Check out some of these intriguing recipes - and feel free to ask us about; we have tried them all, but are working our way through them! 

We are always interested to learn new ways to combat this plant - whether it's through consumption, or some other method!

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Other Knotweed treatment efforts: 

Our partners at the Upper Missisquoi and Trout Rivers (UMATR) Wild & Scenic Committee are offering small grants to landowners who are committed to using mechanical methods to treat a patch of knotweed on their property. Learn more here: https://www.umatrwildandscenic.org/knotweed

Connect with us via phone or email if you have questions about our project, or knotweed in general!

Our thanks to the Lake Champlain Basin Program for the Aquatic Invasive Species Spread Prevention grant that is supporting this project!


 

This project has been funded wholly or in part by the United States Environmental Protection Agency (EPA) under assistance agreement (LC - 00A006950) to the New England Interstate Water Pollution Control Commission (NEIWPCC) in partnership with the Lake Champlain Basin Program (LCBP). NEIWPCC manages LCBP’s personnel, contract, grant, and budget tasks and provides input on the program’s activities through a partnership with the LCBP. The contents of this document do not necessarily reflect the views and policies of NEIWPCC, the LCBP, or the EPA, nor does NEIWPCC, the LCBP or the EPA endorse trade names or recommend the use of commercial products mentioned in this document.

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How we feel about knotweed!

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