Hi John Lampe here. It's a cold crisp day up here in the Northland. I'm a licensed
pesticide applicator in the categories of natural areas and forests. Not a lot
of work at this time of year, so I'm going to step inside and do a
little video slideshow on how to kill Japanese knotweed in three simple steps.
Now I want to be upfront and mention that our company, Green Shoots, sells
products that I think work great for killing knotweed and make mixing and
treating a lot easier. However the basic information I discuss in this video
applies no matter what products you choose to use to control knotweed.
So, what's the big deal with invasive knotweed? Why are naturalist and invasive
species specialists so concerned about it? This photo was taken a few years ago
at a site I worked on with the State Department of Transportation.
The highway department had sprayed the roadside weeds earlier in the year.
Typical roadside weeds are very tough but as you can see knotweed is even
tougher!
Once knotweed really establishes itself it's even worse. It often forms
monocultures like this where nothing else can grow. This is absolutely
terrible habitat for native plants and organisms. However with a little
perseverance and the proper tools, knotweed can be controlled. This is a
site where we did a foliar application of foam herbicide to Bohemian knotweed
with, as you can see, devastating effect. Just remember - after eradicating the
knotweed you will often be left with bare ground where very few native plants
have survived. You must have a plan to restore the area, preferably with native
plants. This video focuses on controlling a small patch of knotweed, the kind of
homeowner might confront. It's specifically designed for the
non-professional. To kill a bigger patch, bigger than let's say 25 square feet,
consider doing a foliar application. Here's a photo of foam herbicide being
applied to knotweed at one of the larger sites we worked at. Foam herbicide works
great for these kinds of sites. However for smaller sites it's recommended that
you use a more targeted application method. That's especially true if you're
applying liquid sprays Those liquid sprays can drift easily and potentially
cause damage to non-target plants. So, what are the three steps for killing
Japanese knotweed? The first step is preparation. This is essential to success.
Before you start, make sure the targeted plant is indeed Japanese knotweed or is
one of the four species of invasive knotweed commonly found in North America. If
you are at all unsure about the species of the targeted plant, ask an expert. In
terms of timing, fall is the best time to do your treatment. This is the time of
year when knotweed plants are transferring sugars down to their underground
rhizomes. Just make sure you treat before a killing frost. A frost will kill the
above-ground parts of the plant, and you won't be able to treat the knotweed
until the following year. The tools you need are straightforward.
Use a pair of loppers if you have big tough stems. For small stems you can use
hand pruners. For most people the biggest obstacle is
figuring out what weed killer to use and how to apply it. The Green Shoots Small
Foam Herbicide Dispenser Package greatly simplifies this task.
The package contains a concentrated glyphosate herbicide. Incidentally,
Swansea University in England recently finished a large research study and
found that glyphosate was the most effective herbicide for knotweed.
The package also contains blue foaming agent that will mark every stem that you
treat. Finally, the dispenser dispenses foam herbicide. Foam herbicide is highly
effective because it keeps the herbicide in a liquid state for a longer period of
time. This increases absorption of the herbicide
by the knotweed. With our method, you are going to be cutting the knotweed stems near
the ground. Before you start cutting, brush off any dirt that you might see at
the bottom of the stems near ground level. The reason for doing this is that
dirt can deactivate glyphosate herbicide. The second step is to cut the
stem about 1 to 10 inches above the ground. The third step is to apply the
herbicide to the cut stump immediately, i.e., within about five minutes of making
the cut. You do this because the stem will seal off
the wound caused by the cut fairly quickly. You want to apply the herbicide
before this happens. Here's a photo of what the foam herbicide looks like on a cut knotweed stem. Notice how thick the foam is. This thick foam is absorbed into
the vascular system of the plant over a long period. Sprays either drip or dry too
quickly. On a side note with this particular application we actually left
the knotweed stem attached to the stump. We did this to test out whether it
increases the absorption of the herbicide. We're going to be continuing
this testing in the future. Repeat the process of cutting and applying the foam
herbicide to all the cut stems. So, cut apply to this one. There is the foam
being applied to the second stump. It is critical that you cut and treat every
knotweed stem in the patch; otherwise the knotweed can survive. Be very careful
with the cut, green knotweed stems. Do not stack them near water bodies. The reason
for this is that knotweed can sprout roots from its nodes. This is the main
way that invasive knotweed spreads. Monitor the location over the next
several years. Kotweed rhizomes can lie dormant underground for years without
sending up shoots. This is one reason that knotweed is so tough to eradicate.
In the patch that you treated you may see some re-sprouts like the ones
shown in this photo. Notice how the leaves of these
plants are a little deformed and don't look like fully-grown knotweed leaves.
This is pretty typical. Often times those leaves are deformed by the herbicide
application. You can either pull these or weed whip them. I would recommend letting
them grow after about midsummer, so that you can do a reapplication to those
leaves with the herbicide in the fall. That's it! Please consider liking this
video; subscribing to our channel; or visiting our website. Most importantly,
get outside and enjoy a native ecosystem near you!