I attended a wonderful conference in Coeur d’ Alene, Idaho, put on by Steve Manning and his group at Invasive Plant Control from December 10-12, 2019.  One theme: rodent eradication!  Dickie Hall, Habitat Restoration Project Director, talked about the complete eradication of rats on the Island of South Georgia.  The island is a treeless tundra not far from Antarctica.  This is a huge win for many bird species that nest on South Georgia (and two species endemic to the island).  The South Georgia Heritage Trust sponsored the restoration.   Dickie also gave a talk on the planned eradication of mice on Gough Island.  The mice eat Albatross chicks and other birds and have devastated avian populations.  I won’t even link to the videos on YouTube which you can easily find if you are so inclined.

Dan Tompkins gave another great talk on making New Zealand predator free by 2050.  This is a massive undertaking to eliminate alien predators (rats, opossums, and stoats) that kill all sorts of native wildlife including the kiwi.

In our work focused on terrestrial invasive plants (not growing on isolated islands) total eradication is nearly impossible.  Nonetheless, these talks were inspiring.  And, anyone who has been on a restored native prairie knows the beautiful sights, sounds, and smells of being in a native landscape.  Perfection is not required!

My talk focused on precision herbicide applications using our Precision Electronic Dispenser.  The key thing to remember about the Green Shoots® products is that they all reduce off-target harm from herbicides.  Traditional high-pressure spray from backpacks inevitably causes off-target harm.  Native plants are highly valuable, especially mature native perennials that may have been alive for as long as 30-40 years.  You should do everything you can to preserve the health of those native plants when you are spot spraying nearby them!

Knotweed monoculture

Knotweed stand – after treatment

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:

1. In a knotweed stand, virtually no light hits the ground.  This prevents other plants and bugs, etc., from living in that patch.
2. New trees cannot grow in a knotweed patch.  This reduces woody debris, for example, in the stream.
3. 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.