What’s the connection between glyphosate and genetically modified crops?

Summary

Over 80% of genetically modified (GM) crops grown worldwide are engineered to tolerate being sprayed with glyphosate herbicides. GM glyphosate-tolerant crops have led to a 239 million kilogram (527 million pound) increase in herbicide use in the US between 1996 and 2011, compared with the amount that would have been used if the same acres had been planted to non-GM crops. People and animals that eat GM glyphosate-tolerant crops are eating potentially high levels of Roundup residues.

Over 80% of genetically modified (GM) crops grown worldwide are engineered to tolerate being sprayed with glyphosate herbicides,1 the best known being Roundup. The herbicide kills all plant life in the field apart from the crop. These crops are known as glyphosate-tolerant or “Roundup Ready” (RR) crops.

The idea behind such crops was to simplify weed control for farmers. The farmer could douse the entire field with glyphosate herbicide, killing all weeds without killing the crop.

But this is not the way things turned out. Weeds have quickly become resistant to glyphosate herbicide through a process called selection pressure, in which only those weeds that tolerate the herbicide survive to pass on their genes. The resulting epidemic of glyphosate-resistant “superweeds” has caused huge problems for farmers in countries where glyphosate-tolerant crops are widely planted.

The area of US cropland infested with glyphosate-resistant weeds expanded to 61.2 million acres in 2012, according to an industry survey. Nearly half of all US farmers interviewed reported that glyphosate-resistant weeds were present on their farm in 2012, up from 34% of farmers in 2011. The survey also indicates that the rate at which glyphosate-resistant weeds are spreading is gaining momentum, increasing 25% in 2011 and 51% in 2012.2 3

GM glyphosate-tolerant crops have led to a 239 million kilogram (527 million pound) increase in herbicide use in the US between 1996 and 2011, compared with the amount that would have been used if the same acres had been planted to non-GM crops. Most of this increase is due to the spread of glyphosate-resistant superweeds,4 which has led to farmers spraying more and more glyphosate to try to control the weeds. As glyphosate becomes increasingly ineffective in weed control, farmers are turning to older, even more potentially toxic herbicides, like 2,4-D, an ingredient of the Vietnam War defoliant Agent Orange, and dicamba.5 6 7 8 9 10 11 12

People and animals that eat GM herbicide-tolerant food crops are eating high levels of residues of glyphosate and its main metabolite, AMPA.13 Both chemicals are toxic.

References

  1. James C. Global Status of Commercialized biotech/GM Crops: 2012. ISAAA; 2012. Available at: http://www.isaaa.org/resources/publications/briefs/44/download/isaaa-brief-44-2012.pdf.
  2. Fraser K. Glyphosate Resistant Weeds – Intensifying. Guelph, Ontario, Canada: Stratus Ag Research; 2013. Available at: http://stratusresearch.com/blog/glyphosate-resistant-weeds-intensifying/.
  3. Farm Industry News. Glyphosate-resistant weed problem extends to more species, more farms. http://farmindustrynews.com/ag-technology-solution-center/glyphosate-resistant-weed-problem-extends-more-species-more-farms. Published January 29, 2013.
  4. Benbrook C. Impacts of genetically engineered crops on pesticide use in the US – The first sixteen years. Environ Sci Eur. 2012;24. doi:10.1186/2190-4715-24-24.
  5. Mortensen DA, Egan JF, Maxwell BD, Ryan MR, Smith RG. Navigating a critical juncture for sustainable weed management. BioScience. 2012;62(1):75-84.
  6. Robinson R. Resistant ryegrass populations rise in Mississippi. Delta Farm Press. 2008. Available at: http://deltafarmpress.com/resistant-ryegrass-populations-rise-mississippi.
  7. Johnson B, Davis V. Glyphosate resistant horseweed (marestail) found in 9 more Indiana counties. Pest Crop. 2005. Available at: http://extension.entm.purdue.edu/pestcrop/2005/issue8/index.html.
  8. Nice G, Johnson B, Bauman T. A little burndown madness. Pest & Crop. http://extension.entm.purdue.edu/pestcrop/2008/issue1/index.html. Published March 7, 2008.
  9. Nice G, Johnson B. Fall applied programs labeled in Indiana. Pest Crop. 2006;(23). Available at: http://extension.entm.purdue.edu/pestcrop/2006/issue23/table1.html.
  10. Randerson J. Genetically-modified superweeds “not uncommon.” New Sci. 2002. Available at: http://www.newscientist.com/article/dn1882-geneticallymodified-superweeds-not-uncommon.html.
  11. Kilman S. Superweed outbreak triggers arms race. Wall Street Journal. http://biolargo.blogspot.com/2010/06/round-up-weed-killer-and-acquired.html. Published June 4, 2010.
  12. Brasher P. Monsanto paying farmers to increase herbicide use. Des Moines Register. http://bit.ly/az3fSo. Published October 19, 2010.
  13. Bøhn T, Cuhra M, Traavik T, Sanden M, Fagan J, Primicerio R. Compositional differences in soybeans on the market: glyphosate accumulates in Roundup Ready GM soybeans. Food Chem. 2013. doi:10.1016/j.foodchem.2013.12.054.

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