A Knotweed Update

July 2, 2020

Written by: Andrea Shortsleeve, Vermont Department of Fish and Wildlife

In our last issue of the VTInvasives e-newsletter, we discussed a new method of treating knotweed by using wire fencing laid horizontally on the ground over a patch of the offending species. Over the past two months, I have received several emails from readers asking some clarifying questions and looking for updates. I apologize for not being able to reply to everyone, and I hope that this article can provide an update with some answers.

As a review, you can read the original article that describes the treatment here.  The idea of using wire mesh to control the growth of knotweed was developed by Dr. Eric Donnelly (I incorrectly referred to him as Dr. Eric Connelly in the previous article), who holds a patent for this technology, which they call MeshTech. A simple Google search will reveal several descriptions on the background of this technology and how it is being used.

Over the past month, I was able to get some fencing down on a small patch of knotweed in a park behind my house. I have also spoken with Lindsey Wight, Coordinator for the Missisquoi River Basin Association, about some tips that she and her crew have learned through their experiment with this method on a few patches of knotweed in their corner of the state. We hope to put together a more comprehensive guide on this method later in the year after we have seen the results of our trial patches, so stay tuned! In the meantime, here are some ideas that we’ve come up with in our experience, along with tips from landowner, Jock Irons, who has been sending me updates on the progress of his knotweed patch (thank you!):

Proper Disposal: If you don’t get the fencing down early enough in the spring before the knotweed starts to grow, you’ll have to cut down and clear out the grown stalks in order to create a space for the wire fence to lay flat. And this means that you’ll have to have a proper method to dispose of the cut stalks. Of course, knotweed being the stubborn invasive that it is will re-sprout from the tiniest fragment, so proper disposal methods are tricky but very important. The best way to dispose of knotweed is burning the material, but you can read more about different disposal methods here.

Overwintering Considerations: We also know we won’t kill the rhizome in one year, and that this method (as with most invasive species treatments) is going to be a multi-year process. This means that the decision will have to be made whether to leave the wire down over the winter or if it will be pulled up and re-installed next spring. Many of the areas where knotweed thrives are also areas that are susceptible to spring flooding or washouts, meaning that removal and re-installation will be necessary. Even though this will increase the amount of work involved, it should be easier over the long run as compared to other treatment methods.

Holding the Wire Down: I’ve been asked by a fair number of people about how they should fasten the wire fencing down to the ground, and honestly, I don’t have a perfect answer. Often the knotweed patches are growing in soil that is loose, already disturbed, and difficult to stake something down in. I was able to use a few extra tent stakes that I had at home combined with landscaping staples. I’ve heard from some landowners that they simply used rocks or heavy branches and other pieces of wood to keep the mesh down. I’m curious about other materials and fasteners that readers have experimented with and had success (or a lack of success) with!

Elevating the Mesh Above the Ground:  In the research that Lindsey and her crew had done, they came across descriptions of this method indicating that keeping the mesh off the ground a few inches was more successful than laying the fencing right on top of the knotweed rhizome. The idea behind this is that the knotweed can potentially send out new roots if the rhizome begins to get crushed by the wire fencing. By keeping the wire a short distance above the ground (using zip ties to secure the mesh to wooden stakes, see photo), the rhizome can send up shoots which will thin out a bit and grow through the holes in the mesh. Again, I’m interested in learning about how landowners have experimented with their own set-ups and what they’ve found success with.

I know that there are a few challenges with this method – the wire is a little expensive for a roll, it can only cover small areas, and steep banks and hills are going to be difficult to get the mesh to lay flat on – but these challenges aren’t anything new to working with invasive species.

Please keep the emails (Andrea.shortsleeve@vermont.gov) coming in and share how you’ve found this method. Any good tips? Any mistakes that you’ve learned from? Any success in putting a dent in your knotweed patch? I look forward to hearing from you!

Photo Credit:

Missisquoi River Basin Association