Glyphosate specifically inhibits an enzyme that is essential to plant growth; this enzyme is not found in humans or animals, contributing to the low risk to human and animal health when using glyphosate-based products according to label directions. The presence of this enzyme in plants, but not in humans and animals, provides a basis for a specific selective toxicity to plant species.
When a Roundup® brand herbicide is sprayed on foliage, glyphosate is absorbed by the plant and then moved – or translocated – throughout the plant's tissues. The surfactant assists the delivery of glyphosate into the plant by attaching itself to the leaf’s waxy surface and breaking it down. Once inside the plant, glyphosate inhibits the activity of an enzyme, which in turn prevents the plant from manufacturing certain amino acids essential for plant growth and life.
After the herbicide application, the plant gradually wilts and turns yellow. Then, as the plant tissue deteriorates, it turns brown. At the same time, the plant’s underground roots decompose. Ultimately, the entire plant dies, and is incapable of regrowth.