摘要：All photosynthesis inhibiting herbicides act only against primary processes that are localised on lipoprotein thylacoid membranes with two reaction centers (photosystem I and II). Triazines, triazinones, uracils, substituted ureas, and pyridazinones are herbicides for pre-emergent or early post-emergent applications in a wide range of crops. These herbicides are uptaken both by roots and leaves with root uptake being prevalent. They are efficient only against emerging weeds or against weeds in early growth stages. In plant, they are transported rapidly by xylem (transpiration flux) into the youngest parts of the plant. Foliar application shows only limited contact efficacy. Benzodiathiazoles, nitrils, phenylpyridazines, and phenylcarbanilates are contact herbicides that are not transported by plant vascular system. Already few days after application chloroses between veins can be found on leaves of sensitive weeds and subsequently leaves necrotise from the edge. The speed of occurrence of external symptoms of herbicide activity is significantly influenced by air temperature and moisture. Paraquat and diquat are non-selective contact herbicides that are used mostly for pre-harvest desiccation of crop canopy or for weed management before sowing or planting. They are not transported by vascular system showing contact effect only. Uptake of these herbicides is in general higher by the absence of light (early evening applications).
关键词：herbicide mode of action; herbicide site of action; inhibitors of photosynthesis; sugar beet; phytotoxicity.
