Expert Insight: Invasive Knotweed

March 3, 2021

Japanese Knotweed is present everywhere along the Upper Delaware River and its tributaries. Left unmanaged it continues to spread along the river and everywhere it can find suitable conditions all the while crowding out native riparian vegetation leading to habitat loss, soil erosion, and bank destabilization.

Friends of the Upper Delaware River (FUDR) is undertaking research to document the extent of knotweed colonization and its impacts on soils and aquatic habitat. This year they are also establishing 3 demonstration sites where landowners can see different options for you to manage, control, or even eradicate knotweed using a variety of low-cost techniques. 

On January 28th, in partnership with FUDR, Penn State’s Shaver’s Creek Environmental Center, and Shippensburg University’s Center for Land Use and Sustainability, we held an informational webinar on knotweed in the Upper Delaware River Watershed and the demonstration sites. You can view a recording of the webinar here.

During the forum, the audience had an opportunity to ask questions. For all the questions we couldn’t get to during the webinar, panelists Dr. Eric Burkhart of Penn State’s Shaver’s Creek Environmental Center and Steve Schwartz, the Knotweed Project Consultant, have since weighed in. See below for their expert insight!

I’m above the Pepacton’s Downsville Dam on the East Branch near Margaretville… I’d love any help I can get. Thanks for this.

Steve responds: Follow our website, www.fudr.org/knotweed and facebook page for more info on knotweed management and site demonstrations

Is digging and selling for resveratrol a possibility?

Steve responds that yes, there are herbal product companies that are purchasing knotweed rhizome.

How many years do you plan to follow the Skinners Falls site?

Steve responds: We have funding for one year. If we can raise additional funding the plan is for two or more years.

The test plots appear to be long and fairly narrow. How will you deal with drift from foliar herbicide application to adjoining test plots? Wouldn’t it better to separate the herbicide plots from the others?

Steve answers: There will be a strip between each plot and foliar is sandwiched between injection and covering.

Landscape architect and riverfront land owner here with half of the property covered with knotweed. Are there partnerships or grants available for landowners to implement these management techniques? Are the products / service providers that were referenced (Geo textile, herbicide, goat rental, herbicide applicator?)

Steve responds: What state are you in? Some federal funding through NRCS may be available, through county conservation districts. Some state level funding is available from time to time though nothing right now. We will share suppliers once we get the project up and running

What about eradication possibilities on state lands, such as state forests, that border the Delaware in several places? Is the State onboard with this problem and trying to solve it?

Steve answers: We have support from NYS DEC for the Skinners Falls project. We suggest advocacy to the state agencies to better address the problem. In NY, CRISP is the agency most involved with knotweed. In PA, there is no equivalent organization.

Our property has a lot of knotweed. We are trying to get it under control by cutting it down constantly and letting our goats and sheep eat it. Is it good to cut down along the river bank as well?

Steve said “Yes!”

How about plowing it up and picking the roots out?

Steve responds: Plowing it might only spread it as the rhizomes are very durable and any rhizome fragments might propagate and then you have the problem of where and how to dispose of all of the rhizomes and root fragments you remove.

How effective is digging it out?

Steve responds: If you have isolated plants it is very effective. In a mature stand it is impossible to get all of the rhizomes and radial roots at one time so it will require repeated management and then you have the problem of disposing the rhizomes without further spreading the plant.

When you mention herbicide. Is there a brand? Or should we keep away from herbicides? (sic)

Steve responds: This glyphosate product is aquatic-labeled and available at Home Depot. It also gives specific instructions for knotweed on pages 9 and 13 of the label. But, it is very important that anyone using herbicide can properly understand and follow all instructions on the label. I haven’t found aquatic-labeled glyphosate products that are ready-to-use (no mixing required).

https://www.homedepot.com/p/1-Gal-Aquatic-Herbicide-53-8-Glyphosate-Concentrate-75298/304755435

While I can see how roundup injection would be more effective than foliar applications, is it practical as a landowner to use a foliar application with a handheld tank sprayer right next to the stream? Doesn’t seem environmentally sound unless one is a prescribed distance from the stream. In the alternative cutting and tarping right next to the stream seems like the most practical and safest practice (until I find a neighborly goat farmer)

Steve responds: Aquatic-labeled herbicide products can be used for foliar applications at the water’s edge. The active ingredient glyphosate is very effective on knotweed.  However, the short answer is we are not promoting using it casually, only providing this an option with precautions and warnings that it should be applied by a licensed professional.

What keeps knotweed in check in its native habitat? Are there any biological controls? And is its original habitat only Japan or other regions of temperate Asia? On the west coast they are having success with biological control. Has it been evaluated here in the east?

Steve responds to both questions: There is a psylid from Japan that has been trialed in the US, UK, and Canada with little success. https://www.youtube.com/watch?v=kPI8_ge8nO0

Do you restrict the goats to the knotweed area so they ONLY eat that? i.e., is knotweed something they eat only when everything else is already consumed?

Steve said: The goats will restricted to test plots which have mature stands of knotweed. Our goat farmer reports that they do eat knotweed and that they seem to like it as it is a novel food source for them. We will try to protect any trees and saplings growing in the plot so that the goats don’t eat the leaves and bark of plants we want to see compete with knotweed.

Any research on planted or natural grass as a deterrent? I’ve seen where lawns grow strong and are absent of knotweed.

Steve replied: Repeated mowing of lawns will deter knotweed. We plan to try sowing various grasses and bushes/trees such as willows as well to see how they can compete.

< Back to Our Work

Related Articles

As part of our public awareness campaign on electric vehicles, Plug It In, NY, we released the second in our series of fact sheets to encourage New Yorkers to make an EV their next vehicle. Our second fact sheet covers everything there is to know about charging an EV.

As part of our public awareness campaign on EVs, Plug It In, NY, we released the first of a series of fact sheets to encourage New Yorkers to make an EV their next vehicle. This first fact sheet dispels myths about charging range which many associate with EVs, known as range anxiety.

We are committed to educating, engaging, and empowering New Yorkers to be effective advocates for the environment. One of our top priorities is reducing greenhouse gas emissions from the transportation sector, New York’s largest source of emissions. Given that there are nearly 11.5 million vehicles registered in NYS, getting individual New Yorkers to make the…

We recently held a forum on reducing emissions from the transportation sector as part of our series on implementing the Climate Leadership and Community Protection Act.

On October 15th, 2020, the New York League of Conservation Voters Education Fund (NYLCVEF), Citizens Campaign for the Environment, and Students for Climate Action (S4CA) held a candidate forum for New York Congressional Districts 1 and 2, which cover a large part of Suffolk County and the southeastern portion of Nassau County. The forum took…

On September 29th, 2020, the New York League of Conservation Voters Education Fund (NYLCVEF) held a candidate forum for New York Senate District 55, which covers parts of Monroe and Ontario Counties, to replace State Senator Rich Funke. The forum took place on Zoom ahead of the general election on November 3rd. NYLCVEF regularly holds…

We recently held a candidate forum for New York State Senate District 1, which covers the east end of Suffolk County. This race will decide who will replace longtime State Senator and environmental champion Kenneth LaValle, who is retiring.

NYLCVEF has released its Clean Bus Guide: a toolkit of resources for community members and groups to launch their own campaign for electric school buses.

We recently held a virtual forum on the role of energy transmission in New York’s plans to expand offshore wind power. The event was co-hosted with Anbaric Development Partners and the Sabin Center for Climate Change Law at Columbia Law School and sponsored by Con Edison.

Get Involved

THANK YOU TO OUR CORPORATE PARTNERS