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

[Art Gover]

Hi, All.

A few quick points.

The brief synopses Damien linked don’t match the content of the linked articles.

The PSU article describes the persistent effect of sub-lethal doses of glyphosate absorbed through thin, pigmented bark.  No dispute with that.  Larry Kuhns at PSU demonstrated that in the 1990’s - nursery treated plants would show symptoms years later after installation in the landscape.  Root absorption is not described.

The Michigan State article emphasized bark absorption of triclopyr, not glyphosate, while treating poison ivy.  Plus, it’s a caution, not an observation.  Also, it does not touch on ester vs. amine formulations, which will likely make a difference.  No negative glyphosate effect described.

The third article has no credibility - no citations and no direct observations.  Summaries of summaries.

Therefore, there really isn’t anything to refute, based on those three sources.

Granted, not necessarily the most useful approach in such matters, but true.  It’s a typical situation - being asked to argue against broad sweeps with narrowly-focused experimental data - i.e. “prove my concerns aren’t valid”, as opposed to asking “what data do you have to support your concerns?"

Dewey makes a great point - it’s complicated, and 1) to date, no one has demonstrated a largely-negative effect of glyphosate on the soil microbiome.  Effects yes, ecosystem-level negative effects, no; and 2) science is not built to support negatives - it is most clear when describing what does happen, not what doesn’t happen.  In this instance, each side of a debate needs to provide their best evidence.  Land managers can provide data showing effects on exudates and therefore rhizosphere microbial communities - but everything we do will impact the soil microflora - physical disturbance, changing light and moisture conditions, changing plants.  Those opposed to herbicides, at this point, cannot provide evidence that using glyphosate to manipulate the composition of a plant community causes a larger negative effect than the presence of the exotic species.

The Relyea papers are a different issue.  Good science, poorly communicated.  He clearly demonstrated the negative impact of certain adjuvants on amphibians.  He did not do a good job of differentiating “Roundup” (meaningless in terms of specific product description) from a specific product with a specific composition of glyphosate and inert (regulatory inert, not biological inert) ingredients.

Be well.

Art

Penn State Wildland Weed Management
116 ASI Building
University Park, PA  16802

(814) 863-9904
(814) 863-6139 FAX
http://plantscience.psu.edu/wildland

> On Oct 18, 2017, at 09:17, Ossi, Damien (DOEE) <damien.ossi at dc.gov> 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
>  
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