Glyphosate as a tool in vegetation management

[Peter Smallidge]

Here is a question I received by email:

Pete,

Have you seen this?  Is it credible?  I'd like to be informed as I poison my beech, ferns and multiflora rose--and as I speak with other landowners.  I appreciate your thoughts.

Monsanto and Genetically Modified Crops - Is there a cover-up?
http://english.pravda.ru/opinion/columnists/19-03-2012/120824-monsanto_genetics-0/

My response:

Thanks for bringing this article to my attention.  I had not seen it.  You asked specifically about this article, to which I’ll respond.  Note first, that I am not an environmental chemist, and others might review this article and reach different conclusions (and share their comments below).  Including the linked article, I am not aware of any legitimate studies that have found sustained problems in a holistic and practical sense with the use of glyphosate, the active ingredient of Roundup (and other products).  That said, there is always the potential of some future discovery, but glyphosate has been around for almost 40 years and is well studied.  

 The article is written by a layman and uses suspicious, borderline scurrilous, logic in developing the arguments.  I am less worried about the author’s credentials (though relevant) and more worried about the way he develops an argument.  I’ll hit a few key points, but for the context in which we use glyphosate on beech etc., this article won’t change my practices.

1. The author tries to link digestive cancers to the use of Roundup (paragraph 3. Why are cancers of the digestive system rising exponentially? Let us start with Monsanto's wonderful herbicide, Roundup.) This is a deceptive, and “faint praise”, stunt to pose a question and then not develop any evidence in support of the suggested argument.  We might also suspect that digestive cancer is linked to poor diets, reduced exercise, high fructose corn syrup, partially hydrogenated vegetable oils, preservatives in foods, etc. 
2. The study in the Journal Microbiology is about the impacts on food bacteria. First, to react in a meaningful way we would need to know how the study was conducted.  They may have found this result under abnormally prolonged exposures or excessive dose rates.  I haven’t seen the original study, but that would be an important step.  Note, however, that we apply glyphosate in forests once per 50 to 100 years and at fairly low dose rates.  Forestry applications are distinctly different from agricultural applications.
3. I just found the study reported (http://www.ncbi.nlm.nih.gov/pubmed/22362186).  The microbes are those found in dairy milk.  For the record I am not a food microbiologist.   The abstract, all that I read, suggests there are effects of Roundup but not effects of glyphosate.  Thus the added surfactants (e.g., soap) impact microbes.  I am not surprised that the surfactants, used in Roundup to break the surface tension of water and facilitate penetration of the active ingredient, are detrimental to microbes.  I am not sure why we would suspect that Roundup would have, in a practical sense, any connection with the food bacteria found in milk. The implication provided by the article, without validation, is movement of Roundup through some ecosystem connection of plants or water, into cows and then through their digestive system to the lactation system and into the milk.  I read the introduction to the article and it doesn't connect these chemicals with changes in milk microbiology, but notes that bacteria in milk have changed through time. Perhaps this connection exists.  The report says that glyphosate is found in all samples of groundwater in the US.  This might be so, but we don’t know the quantities of glyphosate in water samples, plus the glyphosate in the study lacked the impacts that the Roundup had.  Current environmental chemistry can detect very small amounts of compounds, well below what are known to cause any problems.  There wasn’t mention of Roundup in ground water.
4. Related to #2.  Glyphosate’s mode of action is to interrupt the biochemical pathway of an enzyme used in photosynthesis.  Humans lack that enzyme (of course) because we don’t photosynthesize.  I understand that glyphosate binds tightly to organic matter in the soil and thus isn’t in soil water solution.  This is in contrast to the comments in #3.  The half-life of glyphosate, for 50% to degrade, is on the order of a couple weeks as I recall.  The LD50 for glyphosate, the quantity needed to kill 50% of a population of mice, is higher than the quantity of table salt or caffeine.  Details of the basic chemistry and toxicology of glyphosate are here http://pubs.cas.psu.edu/freepubs/pdfs/UH174.pdf   As a side note, the LD50 only assess acute toxicity, and does not describe any types of low-level chronic exposure. 
5. The article centers on the use of “Roundup Ready” (RR) agricultural plants (corn, soybeans, etc.).  This is different in type and degree from our use in the forest.  RR plants are genetically breed to lack sensitivity to glyphosate.  Thus, farmers plant RR crops and spray them with Roundup to kill the associated weeds.  Traditionally farmers would rotate crops and thus cultural practices and herbicides used.  Rotation helped reduced weed problems because of the diversity of techniques.  The variation of treatments would keep the weeds at bay.  By using primarily RR crops, the same crop is used repeatedly and weeds that have a natural resistance to glyphosate survive to reproduce.  If farming would again employ some rotational techniques, the abundance of weeds that lack sensitivity to glyphosate would likely be controlled.  With the advent of RR crops, the use of glyphosate has increased about 10 fold.  Remember, our forestry context includes primarily limited and selective treatments.  The likelihood we develop “super beech” is unlikely given the dose and frequency of treatments.
6. I didn’t count, but many of the author’s claims of concern were actually reports of allegations.  These are baseless as evidence against the use of a product or person.
7. My final assessment after thinking through these points: (a) The article is poorly documented and doesn’t develop sound arguments to support its conclusions.  It doesn’t really give conclusions, just uses innuendo to create a perception of problem. The unsupported argument is that glyphosate used in RR crops impacts the food bacteria of milk. The quality of the article leads me to doubt all its claims. (b) I am not sufficiently versed in practices of agricultural production to offer a good perspective on the RR crops and how this relates to bacteria in milk.  The article only alluded to a connection and didn’t report that there were any changes in the bacteria found in milk. (c) Our use of glyphosate products in forestry applications is strikingly different from agricultural practices.  This doesn’t mean we don’t need to follow label guidelines or that agricultural practices are bad.  (d) The use of glyphosate, or other herbicides, needs to be weighed against the human and ecological cost of not using these herbicides.  To suggest that a tool shouldn’t be used because it has impacts to other characteristics of the ecosystem would eliminate all our tools. This argument doesn’t validate a tool, but suggests a better reason for exclusion is needed.  (e)  All things considered, it would be problematic to not include glyphosate products in our tool box for vegetation management.  The principles of integrated vegetation management (IVM) apply, where we consider all tools, strive to practically reduce the use of herbicides, consider a variety of tools in an appropriate sequence, and seek an ecologically and economically favorable outcome.

Comments and thoughts welcome.

Peter