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How does glyphosate kill plants?

Category: Herbicide Operations

Glyphosate-based herbicides are absorbed by the leaves of plants. Once there, the chemical prevents the production of a plant-specific enzyme necessary for survival. This enzyme is only found in plants, which is why glyphosate has such low toxicity in animals and humans. Glyphosate is strongly bound by organic matter and clay in soils and thus glyphosate residues are very unlikely to be taken up by seeds, new germinants or into plant roots. This allows forest vegetative communities to redevelop quickly on sites following treatment

Glyphosate-based herbicides are nonselective, moving systemically throughout plants once they penetrate their leaf cuticles. However, since they are typically highly water soluble, they do not penetrate waxy cuticles well and require the use of a surfactant (a detergent) to enhance transfer across this protective barrier. Once inside the plant, glyphosate functions by inhibiting a very plant-specific enzyme necessary for synthesizing essential amino acids. This particular enzyme does not occur in animals and humans, thus glyphosate itself has very low acute and chronic toxicity levels in these organisms.

Glyphosate-based herbicides are also very strongly bound to organic matter and clay particles in soils. As such, they are deactivated by soils and have no ability to control plants that sprout from seeds in the soil seed bank or from the roots or rhizomes of untreated plants (How long does glyphosate remain in the soil, water, plants and sediments after treatment?). This is advantageous from an environmental perspective because it assures that sites will develop diverse vegetative communities within a few years following treatment.