Monitoring Photosynthesis to Measure Translocation of Bentazon in Common Cocklebur

The movement of biologically active levels of benta- zon (3-isopropyl-lH-2,1,3-benzothiadiazin-(4) 3H-one 2,2-di- oxide) was followed by monitoring photosynthetic activity of plant parts after application of the herbicide. Bentazon was applied to roots, stems, petioles, portions of the canopy, and portions of individual leaves of 4- to 24-day-old common cocklebur (Xanthium pensylvanicum Wallr.) at rates compa- rable to field application rates. Application of bentazon any- where on the plant either slowed or stopped photosynthesis in leaves acropetal to the point of application. Contact of benta- zon with stems, petioles or roots contributed to the phytotoxi- city of the herbicide.