Herbicidal activity and selectivity of new 3‐alkyl‐4‐amino‐6‐aryl‐1,2,4‐triazin‐5‐ones

Abstract 3‐Alkyl‐4‐amino‐6‐phenyl‐1,2,4‐triazin‐5‐ones are herbicidal compounds which act by inhibition of the electron transport in photosynthesis (Hill reaction). There is some correlation between phytotoxicity and photosynthesis inhibition data. An exception is found with sugar beets which are very tolerant towards triazinones with a methyl group in 3‐position and an amino group in 4‐position. The best compound from this series, 4‐amino‐4,5‐dihydro‐3‐methyl‐6‐phenyl‐1,2,4‐triazin‐5‐one, metamitron, shows very promising properties as a selective herbicide in sugar beet crops.