Henry Grabar wrote an excellent piece in Slate on knotweed: “Oh, No, Not Knotweed! What I think is so important about this article is that it lays out the environmental consequences of knotweed – not just the potential for property value losses that are so widely reported about in the United Kingdom. Knotweed is especially devastating to waterways. The article notes the three key problems with knotweed identified by Chad Hammer at the University of New Hampshire:
- In a knotweed stand, virtually no light hits the ground. This prevents other plants and bugs, etc., from living in that patch.
- New trees cannot grow in a knotweed patch. This reduces woody debris, for example, in the stream.
- Erosion! Patches of knotweed have very little organic matter on the ground and the ground can erode easily.
Especially with flood events becoming more common – and water washing live, viable knotweed debris downstream – the problem will only get worse.
Knotweed can be controlled! The above photos show that an aggressive treatment can virtually eliminate it. The key is to keep after the straggler plants that will inevitably persist after the initial treatments. Here is our YouTube video: How to Kill Knotweed: 3 Simple Steps for the Non-Professional.
This is an impressive 2018 study on treating Chinese privet (Ligustrum sinense) with herbicide: Enloe et al., The Influence of Treatment Timing and Shrub Size on Chinese Privet (Ligustrum sinense) Control with Cut Stump Herbicide Treatments in the Southeastern United States. Note also that the study has good advice for treating many different kinds of woody invasives that are prone to lateral sprouting – tree of heaven being another prominent one. Here’s specifically what I like about the research they conducted.
First, the researchers used good technique for doing cut stump treatments. They cut the stump low to the ground – about 1 inch above ground level. Anecdotally, I have found that cutting the stump low to the ground makes a difference in the success of the treatment.
The researchers applied the herbicide immediately after making the cut – within 30 seconds. It is not known how quickly woody plants seal off wounds to live tissue; however, research does indicate that plants can react to physical wounds very quickly – within minutes. Why take a chance? Treat quickly after making the cut.
Second, the investigators did good follow-up. They didn’t just look at whether the stumps had re-sprouts. They also looked at sprouting from lateral roots within a 30 cm radius. The researchers checked the stumps at 6, 12, and 18 months after treatment. Most of the treated privet stumps likely died within the first 6 months in this study. However, as the authors note, that is not necessarily the case with different species of invasive woodies.
Third, the study reached important conclusions that really provide guidance to those in the field. It found that November treatments were more effective than April ones – 95% vs 87% mortality. The study found that glyphosate outperformed triclopyr in the November treatments – 97% to 91% control. The authors note that this suggests that “glyphosate is more effective than triclopyr for controlling species prone to lateral root sprouting.”
Finally, the authors found that lower than labeled concentrations of herbicide were effective at controlling privet. This conclusion may not be applicable to all species, but it does suggest that you should be safe using the lowest rates recommended on the label for cut stump and cut stem treatments.
We launched our new website! Please take a look: Green Shoots.
Check out our newest video How to Kill Invasive English Ivy Vines: 3 Steps. If you like PowerPoint presentations better, here it is: PowerPoint How to Kill English Ivy Vines. We will be publishing another set of presentations on killing English ivy groundcover. For that we recommend a foliar or wipe application. English ivy can be a real problem in many parts of the world. It can climb tall native trees and eventually even kill native trees. As a groundcover, it also can out-compete natives. One thing: English ivy can be controlled in the winter when many native plants are dormant.
At Green Shoots, we sell concentrated weed killer and our foam herbicide dispenser systems help you
apply that weed killer precisely and with low drift. Concentrated weed killer or herbicide is not just more economical. It is also more effective.
Read this paper (link) from Bryan Young, currently a professor at Purdue about glyphosate rates. In it he says: “The most consistent application factor that can increase glyphosate efficacy is lower carrier volumes.” What does Professor Young mean by this? He means that by adding less carrier (i.e., water) and increasing the amount of glyphosate herbicide (i.e., increasing the herbicide concentration) in the spray solution, the herbicide is more effective. Moreover, this is the case even though an application may cover less of the target plant.
Take a look at the photos below and this video to see before and after images of weeds treated with low volume/high concentration applications: Video (link). As you will see in the foliar applications, very small amounts of herbicide are applied to very small areas of foliage (probably covering less than 10% of the green foliage). In spite of the small amount of coverage, the weeds were completely killed.
This presentation at the Upper Midwest Invasive Species Conference, 2014, summarized some of our control work on invasive knotweed at Southwood Nature Preserve in
the Twin Cities Metro area. It also briefly discusses use of our foam herbicide system by the Northeast Iowa RC&D where they have had success treating a large infestation of greater than 25 acres. Finally, Washington State
University did some testing this summer comparing our foam herbicide dispenser to traditional spraying techniques. So far (and these results are very preliminary), the foam herbicide has performed better than the spray even though half as much herbicide was used on the plots where foam was applied. The full presentation is online at: How to Kill Japanese Knotweed.
As soon as we get data from Washington State University on their testing of the foam system, we will provide a link or other information.
We just added a new page with testimonials about our products. Here it is: Testimonials (link). They will give you an idea about what people are doing with our foam herbicide dispensers!