Glyphosate Stewardship: Maintaining the Effectiveness of a Widely Used Herbicide (original) (raw)

Glyphosate Stewardship: Maintaining the Effectiveness of a Widely Used Herbicide G lyphosate has been used since it was registered in 1974 under the trade name Roundup. It is a foliar-applied herbicide that readily moves throughout the plant, both in phloem (tissue that moves carbohydrates) and xylem (tissue that moves water). Because of its net negative charge, it tightly binds to phosphate sorption sites on soil and organic matter; therefore, glyphosate very rarely exhibits soil activity. It is an effective herbicide for burndown treatments to control weeds before planting. In addition, it is widely used in orchards and glyphosate-resistant crops. Glyphosate kills plants by inhibiting a particular enzyme, 5-enolpyruvyl shikimate-3-phosphate (EPSP) synthase. This enzyme is one of several in the shikimic acid pathway, which is how plants produce the aromatic amino acids phenylalanine, tyrosine, and tryptophan. Amino acids are building blocks for the plant, so a plant not able to manufacture all amino acids is unable to grow and develop normally. Plants also use these three specific amino acids to synthesize more complex structural compounds (such as lignin) and a host of plant defense molecules (such as alkaloids, cyanogenic glycosides, coumarins, and flavonoids), which together can make up 60 percent of a plant's dry weight. Consequently, inhibition of this pathway causes serious