Mode of Action of commonly used Herbicides and their Impact on Crops and the Environment

Commercial herbicides exhibit many different mechanisms of action. Several enzymes involved in biosynthesis of amino acids are sites of action for herbicides. Many different herbicide classes inhibit photosynthesis by binding to the quinone-binding protein, D-1, to prevent photosynthetic electron transfer. Modern herbicides are often synthetic mimics of natural plant hormones which interfere with growth of the target plants. At low doses, it promotes plant growth while at high doses it drives plant overgrowth causing stunting and twisting of stems, and general abnormal growth in plants. Farmers quickly adopted glyphosate for agricultural weed control after the development of glyphosate resistant crops that kills weeds without killing the crops. Some herbicides are known to have more than one site of action. Virtually all knowledge of herbicide structure-activity relationships is semiempirical. In addition to site of action structure-activity relationships, herbicide structure and chemical properties also strongly influence absorption, translocation, bioactivation, and environmental stability. The use of adjuvants may enhance the activity of herbicides.