[MAIPC] Glyphosate's effects on trees and soil microbia

Fri Oct 20 08:40:57 PDT 2017

Damien,

I read through the articles you have links to below.  It appears to me that the Penn State Extension and the Michigan State Extension articles are being mis-quoted.

1.       For the Penn State article I did not see anything that said as listed below: "Tree roots absorb glyphosate; it has a much longer half-life than when it is in the soil."  Maybe I missed it.  Also, it said for a "Mis-application,"  not as quoted below:   A single glyphosate application results in ,persistent stunted leaf growth.  The entire article was concerning mis-applications and possible impacts on non-target plants and how to avoid that.  If used properly these things should not be a concern.

2.       Michigan State: Even this is a mis-quote.  It states below: Herbicides that touch the bark of mature, healthy trees may be absorbed by the outer bark and negatively affect the adjacent vascular tissue.  The article actually says: "Keep in mind that mature trees can potentially be harmed by triclopyr. Since poison ivy will grow up tree trunks, you may be tempted to spray the leaves and vine on the trunk. This is rarely a good idea. In some cases, the herbicide may move through the outer bark and into the tissue the trees needs to transport water or nutrients. This can severely damage or even kill healthy, mature trees."  This is correct, the ester formulation of triclopyr can be moved through the bark of trees.  If the vine is attached to the tree it says to cut it and spray the cut surface.  Even Art Gover's fact sheet (Penn State) provides similar information on controlling woody vines:  http://plantscience.psu.edu/research/labs/weed-ecology/research/wildland-weed-management/publications/invasive-species-quicksheets/woody-vines   "However, treating all the vines on a well-developed infestation with stem treatment is challenging, or not practical at all if the vines are wrapped around desirable trees. "If you use an oil-soluble product such as 'Pathfinder II' (triclopyr), do not get the spray on the bark of desirable trees and shrubs."

3.       As for the third reference, I would have to see the actual published research papers she is quoting.  In addition, the article states: "Glyphosate can significantly damage the overall health of a tree that absorbs it into its roots."  Glyphosates binds to soil particles and has no soil activity.  It is not absorbed by tree roots.  However, if a trees is sprayed on the foliage with glyphosate it will translocate it to the trees roots as it is a systemic herbicide.  And yes, it can significantly damage a tree in that case.

Here is a link to a publication that may be of some assistance to you.  I have used it often: Environmental Safety of Forestry Herbicides - https://store.aces.edu/ItemDetail.aspx?ProductID=15774

Hope that helps.
Dave Jackson

David R. Jackson
Forest Resources Educator
Penn State Extension-Centre County
Willowbank Building, Room 322, 420 Holmes Street
Bellefonte, PA 16823
drj11 at psu.edu<mailto:drj11 at psu.edu>         814-355-4897(office)         814-355-6983(fax)
Forest Resources Extension:  https://extension.psu.edu/forests-and-woodlots<http://extension.psu.edu/natural-resources>
Central Pennsylvania Forests: http://www.centralpaforest.blogspot.com/

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From: MAIPC [mailto:maipc-bounces at lists.maipc.org] On Behalf Of Marc Imlay
Sent: Wednesday, October 18, 2017 6:49 PM
To: 'HTI Gmail'; 'Ossi, Damien (DOEE)'; 'MAIPC Listserve'
Subject: Re: [MAIPC] Glyphosate's effects on trees and soil microbia

Because we target the glyphosate very carefully the amount of glyphosate is about 10-20% of broadcast treatment.

Marc Imlay, PhD, Chair, Biological control working Group Conservation biologist, Park Ranger Office, Non-native Invasive Plant Control coordinator. Marc.Imlay at pgparks.com<mailto:Marc.Imlay at pgparks.com>
(301) 442-5657 cell  Natural and Historical Resources Division
The  Maryland-National   Capital   Park  and Planning Commission

From: MAIPC [mailto:maipc-bounces at lists.maipc.org] On Behalf Of HTI Gmail
Sent: Wednesday, October 18, 2017 11:07 AM
To: Ossi, Damien (DOEE) <damien.ossi at dc.gov<mailto:damien.ossi at dc.gov>>; MAIPC Listserve (maipc at lists.maipc.org<mailto:maipc at lists.maipc.org>) <maipc at lists.maipc.org<mailto:maipc at lists.maipc.org>>
Subject: Re: [MAIPC] Glyphosate's effects on trees and soil microbia

Damien

Very prescient timing.  I am just now reading "The Hidden Half of Nature" which is a good presentation of soil ecology for the layman.

I am impressed by the interaction among bacteria, fungi and plants in the rhizosphere of plant roots.  The discussion of how the agrichemical culture disrupts the effectiveness of microbe ecology (reducing the beneficial microbes that consume plant exudates thus allowing the pathogenic microbes to dominate) is pretty convincing.

While this is not a definitive argument against glyphosate, it does give some credence to the premise of those concerned.

The counter argument of course is that we have used glyphosate for years to manage invasive species and the soil ecology seems to recover.  Also, I would weigh the relative risks of allowing invasives to take over (with the resulting impact of THEIR exudates on the soil ecology) vs. keeping them at bay and maintaining the soil ecology that is decided that "should" be there.

I really think the issue is the long term relative risk of non treatment vs. treatment.  Even if there are definitive data to demonstrate that glyphosate harms the soil ecology, what is that impact relative to allowing a monoculture of stiltgrass (or WLBG) develop?  We KNOW (I think?) these invasives have extensive and long term impacts on soil ecology.

Kind of like oral contraceptives.  We know there are risks associated with their use.  But, those risks are minuscule compared to the risks associated with pregnancy and child birth. (used to work in maternal health).

Will follow this discussion with interest!  Thanks for bringing it up.

Regards,

Dewey Clark

Club Naturalist

Co-District Manager (PA)

Potomac Appalachian Trail Club

Maryland Master Naturalist
On 10/18/2017 9:17 AM, Ossi, Damien (DOEE) wrote:
I am trying to convince the land managers in my city (Greenbelt, MD) to start managing the invasive plants on some of their land.  I am getting some pushback from a community group that says there's proof that glyphosate will kill or damage trees and soil biota.  I've been looking for published papers that would support of refute their arguments, but have been unable to find much. (I don't have access to JSTOR, BioOne, etc.)

They are citing the following documents:

(1) Pennsylvania Extension Service:  Tree roots absorb glyphosate; it has a much longer half-life than when it is in the soil.  A single glyphosate application results in ,persistent stunted leaf growth. https://extension.psu.edu/use-glyphosate-with-care-near-trees

(2) Michigan Extension Service: Herbicides that touch the bark of mature, healthy trees may be absorbed by the outer bark and negatively affect the adjacent vascular tissue. http://msue.anr.msu.edu/news/be_careful_where_you_spray_that_stuff

(3) Glyphosate interferes with the ability of tree roots to absorb manganese, zinc, iron, and boron from the soil; resulting in root rot, reduced cold hardiness, and reduced drought hardiness. http://homeguides.sfgate.com/effect-glyphosate-tree-roots-29076.html

Does anyone have any resources that address these issues, or is there any known comprehensive document that reviews and summarizes independent research on the effects on glyphosate in forest ecosystems?

Thanks,

Damien

Damien P. Ossi
Wildlife Biologist
Fisheries and Wildlife Division
Department of Energy & Environment
Government of the District of Columbia
1200 First Street NE, 5th Floor
Washington, DC 20002
Desk: (202) 741-0840
Web: doee.dc.gov<http://www.doee.dc.gov/>

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