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Should I kill invasive trees with herbicides?

by on September 13, 2013

Photo: Starr Environmental.
Photo: Starr Environmental.

In this installment from Bay Nature’s Ask the Naturalist series, we address the thorny issue of whether to use herbicides on invasive plants.

Question: I have a few (fairly young) invasive trees growing in my garden. I would like to kill them by drilling holes in their trunks and injecting Roundup. Will this method work and is there any danger of contaminating the surrounding soil?— Jocelyn Gibson, Oakland


Provided by Lech Naumovich, botanist and Executive Director of the Golden Hour Restoration Institute

An herbicide is a very powerful, albeit controversial tool. Certain invasions are nearly impossible to treat without herbicide, but I always make sure I’ve considered all other non-chemical modes of treatment first.  When applied correctly by a professional, industry-driven research demonstrates that many common herbicides have minimum long lasting effects in natural systems. Notably, there are also certain herbicides that are extremely toxic to both people and our natural environment.

Herbicide by-products (when the active compound breaks down) are less frequently studied and many opponents believe by-products can be more toxic than the EPA-approved active ingredient. It would be against my better judgement to predict herbicide movement and biochemical pathways in living systems. What we do know is that many herbicides have surfactants (in addition to the active ingredient and byproducts) that have well known, widespread impacts on biological systems.  All this is to say that herbicides are powerful tools to be wielded with extreme care.

Herbicide selection, timing and the target plant are the key variables to consider. I see about 90% of errors occur at this planning stage, wherein the wrong herbicide is selected, or timing is poorly planned. In my experience, applying herbicide at the incorrect time in the plant’s life cycle is the most common error amateur applicators make. I recommend you contact a professional who can identify your weed problem, is well-learned on various treatment techniques, and knows how to effectively apply the herbicide if that is the recommended course of action.  In fact, you may not even require the use of herbicide for proper control of a target species. I would contact the California Invasive Plant Council for leads on local professionals.

Please be safe and extremely mindful with herbicides as their misuse is known to cause grave environmental impacts including damaging aquatic systems and impacting adjacent plants with poorly targeted application. Hiring a knowledgeable professional may end up saving you money, reducing environmental impact, and making your treatment more successful.

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A Place and Time for Herbicides | on September 17th, 2013 at 5:24 pm

[…] Bay Nature Institute reached out to us and asked for a written response to an herbicide question posted in the “Ask a Naturalist” column. Here’s the link. […]

Janet Gawthrop on October 9th, 2013 at 10:28 am

The question asked was removing young invasive trees, but did not say how young. I’ve found that some young trees put out a lot of top growth, but can still be dug out or removed with a weed wrench. In particular, you can do this with some Eucalyptus globulus and Acacia species, especially in wet soil. Of course, once the roots get established after a year or two, then you have a much more difficult problem.

Lech on October 9th, 2013 at 10:56 am

Hi Janet,
Thanks for the thoughtful response. You’re absolutely correct that age of plant should be considered. I also lean towards hand removal of younger woody plants since this can be an effective control without any herbicide application. I presumed that since the weeds were noted to have “trunks” that they were larger plants wherein hand pulling may not be an option. Weed wrenches can be a great tool to extend the “range” of what we can handpull.

Bev on October 24th, 2013 at 8:13 pm

My experience with stories of friends “hiring a professional” has meant a permanently contaminated/poisoned land/property, with the “professionals” outright lying, using banned pesticides, and doing more than promised.

At this point, I don’t believe there can ever be a justified reason for using poisons when the result is chronic illness and cancer, for those exposed (including in the future — I can still smell the pesticide used at a friend’s house for termites 37 years ago which was completely unnecessary since it’s quite easy to eliminate termites safely, and which was likely the now-banned chlordane — and is that why my friend has had two separate rare, extremely invasive cancers?) — and for those subjected to the toxins from the factories where the poison is made.

The “professionals,” like Monsanto have an invested interest in pushing their product and making money. They will deny the extent of the damage they do, like the man who supervises county roadside spraying who pretended he’d never seen what I saw, which was a California Newt dying a horrible death after walking through a sprayed area. It’s all about money, which is why they continue spraying “to prevent fires,” even though the dried dead plants covered with petrochemicals will be more flammable than just leaving the plants staying green longer or just dying naturally.

Spraying our local parks is completely unnecessary, yet it’s increasing, even right next to endangered species’ habitat.

There are always other ways to deal with trees and other plants than by permanently contaminating the environment. I’ve heard that spraying is the only way to kill Blackwood Acacia, but I’ve found it’s quite easy to just cut it down until it stops growing. But who would make money from that?

Lech on November 1st, 2013 at 7:07 am

Hi Bev,
I do appreciate your input. I think you’ve brought up some critical points that deserve more discussion than I can provide in a blog post. I was trying to be clear about the mindful and strategic use of herbicides.

I always consider other strategies before using chemical treatments -and urge everyone the same.

I’m sorry you had a bad experience with professionals, but maybe I should have qualified that noun with “well-qualified and ecologically minded” professionals. In fact, many professionals do use mechanical, cultural and other control methods before chemical and they make money and keep clients happy and nature intact.


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