Technical Abstract: Weed management in most agroecosystems has become largely dependent on synthetic herbicides because of their high level efficacy and relatively low cost compared to other weed control technologies. By volume, herbicides are the most abundantly used category of pesticides applied in agriculture. The molecular target sites are known for almost all of the several hundred synthetic commercial herbicides. Less than twenty molecular target sites are known to be shared by these compounds. These include proteins associated with energy transfer in photosynthesis, auxin function and transport, protein dephosphorylation, microtubule function, and synthesis of amino acids, carotenoids, chlorophyll, plastoquinone, folate, fatty acids, and cellulose. Two herbicides divert energy from photosystem I to generate reactive oxygen species. Because herbicides are such good inhibitors of certain enzymes and protein functions of target sites normally not found in animals, these molecules have been used extensively in the study of plant physiology and biochemistry to probe the functioning of plants. In general, their toxicity is strictly regulated to be specific for plants with little or no toxicity towards non-target organisms, especially mammals.