Herbicides and plants

Summary Herbicide activity depends upon the inherent ability of the active ingredient (AI) to interact with the target enzyme(s) and the efficiency of its delivery at the target site(s). In this paper consideration is given to the factors which influence effective target site delivery and activity of foliage and soil-applied compounds. In the case of foliage- applied herbicides, the efficiency of retention and cuticle penetration is influenced by the stage and habit of growth of the plant, leaf age and surface characteristics, the molecular and formulation features of the AI, and the environmental conditions before, during, or after spraying. These factors may influence the efficiency of uptake, translocation and metabolism of AI en route to the target sites. The action of soil-applied compounds is influenced by the physico-chemical properties of the AI, its adsorption/desorption on the clay-humus colloidal complex, and the absorption, transport and metabolism en route to the target sites. In particular the water solubility of the AI, its formulation and the climate conditions subsequent to spraying, may influence selectivity and environmental fate. Finally, the ability of plants to acquire herbicide tolerance is considered in relation to both crop and weed with particular reference to the mechanisms which can be used to induce tolerance in crop plants.