The history and current status of glyphosate

Authors: Duke, Stephen

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2017
Publication Date: 6/28/2017
Citation: Duke, S.O. 2017. The history and current status of glyphosate. Pest Management Science. 74:1027-1034. doi:10.1002/ps.4652.
DOI: https://doi.org/10.1002/ps.4652

Interpretive Summary: Glyphosate has been called a once-in-a-century herbicide. Since it was commercialized in 1974, its use has grown to dominate and shape the herbicide marketplace. In 2008, half of the U.S. herbicide market, as measured by amount applied, was glyphosate. Much of this use was on transgenic, glyphosate-resistant (GR) crops, which have been the dominant transgenic crops worldwide. The combination of GR crops with glyphosate provided the most effective and inexpensive weed management technology in history for a decade or more. However, the dominance of glyphosate and GR crops are eroding due to the rapid increase in weed species that have evolved resistance to glyphosate (ca. 35 since 1996). Glyphosate is the only herbicide to target the enzyme 5-enolpyruvyl-3-shikimate phosphate synthase (EPSPS). It is a high use rate, non-selective herbicide. After application, it translocates primarily to metabolic sinks, killing meristematic tissues away from the application site. Thus, it kills subterranean tissue, making it an effective herbicide for perennial weeds. Its slow action allows the herbicide to move throughout the plant. Although glyphosate chelates divalent metal cations, the complete resistance to glyphosate of transgenic plants with transgenes encoding GR EPSPS indicates that this property does not contribute to the herbicidal activity or cause any significant changes in plant mineral nutrition. Glyphosate is toxic to some plant pathogens, and thereby can act as a fungicide in GR crops. Ultra-low doses of glyphosate stimulate plant growth by unknown mechanisms. Despite rapid and widespread increases in GR weeds, glyphosate use has not decreased. However, as GR weeds increase other technologies will eventually lead to decreased use. Glyphosate and its changing role in agriculture continue to be fascinating topics.

Technical Abstract: Glyphosate has been called a once-in-a-century herbicide. Since it was commercialized in 1974, its use has grown to dominate and shape the herbicide marketplace. In 2008, half of the U.S. herbicide market, as measured by amount applied, was glyphosate. Much of this use was on transgenic, glyphosate-resistant (GR) crops, which have been the dominant transgenic crops worldwide. The combination of GR crops with glyphosate provided the most effective and inexpensive weed management technology in history for a decade or more. However, the dominance of glyphosate and GR crops are eroding due to the rapid increase in weed species that have evolved resistance to glyphosate (ca. 35 since 1996). Glyphosate is the only herbicide to target the enzyme 5-enolpyruvyl-3-shikimate phosphate synthase (EPSPS). It is a high use rate, non-selective herbicide. After application, it translocates primarily to metabolic sinks, killing meristematic tissues away from the application site. Thus, it kills subterranean tissue, making it an effective herbicide for perennial weeds. Its slow action allows the herbicide to move throughout the plant. Although glyphosate chelates divalent metal cations, the complete resistance to glyphosate of transgenic plants with transgenes encoding GR EPSPS indicates that this property does not contribute to the herbicidal activity or cause any significant changes in plant mineral nutrition. Glyphosate is toxic to some plant pathogens, and thereby can act as a fungicide in GR crops. Ultra-low doses of glyphosate stimulate plant growth by unknown mechanisms. Despite rapid and widespread increases in GR weeds, glyphosate use has not decreased. However, as GR weeds increase other technologies will eventually lead to decreased use. Glyphosate and its changing role in agriculture continue to be fascinating topics.