The history and current status of glyphosate

Abstract

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 that translocates primarily to metabolic sinks, killing meristematic tissues away from the application site. Its phloem-mobile properties and slow action in killing weeds allow the herbicide to move throughout the plant to kill all meristems, making it effective for perennial weed control. Since commercialization in 1974, its use has grown to dominate the herbicide market. Much of its use is on transgenic, glyphosate-resistant crops (GRCs), which have been the dominant transgenic crops worldwide. GRCs with glyphosate provided the most effective and inexpensive weed management technology in history for a decade or more. However, as a consequence of the rapid increase in glyphosate-resistant (GR) weeds, the effectiveness of glyphosate use in GRCs is declining. Critics have claimed that glyphosate-treated GRCs have altered mineral nutrition and increased susceptibility to plant pathogens because of glyphosate's ability to chelate divalent metal cations, but the complete resistance of GRCs to glyphosate indicates that chelating metal cations do not contribute to the herbicidal activity or significantly affect mineral nutrition. The rates of increases in yields of maize, soybean, and cotton in the USA have been unchanged after high adoption rates of GRCs. Glyphosate is toxic to some plant pathogens, and thereby can act as a fungicide in GRCs. Ultra-low doses of glyphosate stimulate plant growth in glyphosate-susceptible plants by unknown mechanisms. Despite rapid and widespread increases in GR weeds, glyphosate use has not decreased. However, as GR weeds increase, adoption of alternative technologies will eventually lead to decreased use. Published 2017. This article is a U.S. Government work and is in the public domain in the USA.

Overview of glyphosate‐resistant weeds worldwide

“…Even though glyphosate is a herbicide for which there is a comparatively low risk for evolution of resistance,, resistance is evolving at a rapid pace. But, the selection pressure with glyphosate has been over much greater land areas for extended periods, unlike that for any other herbicide class . The mechanisms of resistance evolved for glyphosate are more diverse than for any other herbicide mode of action …”

<b>Glyphosate efficacy on sourgrass biotypes with suspected resistance collected in GR-crop fields

“…For over 20 years there were no reports of glyphosate resistance in weeds (Duke, 2017). However, the first glyphosate resistant species, Lolium rigidum, was found in an Australian field in 1996 (Heap, 2017).…”

“…Since then, the number of resistant sourgrass cases has increased considerably in the country (Cerdeira, Gazziero, Duke & Matallo, 2011). The rapid adoption of GR crops and the loss of the glyphosate patent by Monsanto in 2000 were decisive factors for its widespread adoption as the main tool to control weed sin GR crops (Duke & Powles, 2008;Duke, 2017).…”

Agricultural GMOs—What We Know and Where Scientists Disagree

“…As for the former, resistance to pesticides is not unique to GMOs and there are hundreds of non-GMO examples of herbicide resistance developing in weeds [39]. In the case of glyphosate, despite first being used in the USA market in 1974 and having its use become widespread following the introduction of the first glyphosate-tolerant crops in 1996, glyphosate maintains its effectiveness against most weeds, and 90% of farmers of cotton, maize, and soybean in the USA choose to continue to plant a glyphosate tolerant crop and to use glyphosate [40]. As weed resistance does inevitably increase, however, there are strategies that can be used to maintain effectiveness of HT varieties, even in the presence of resistance.…”