Abstract
Chlorotriazines, simazine, propazine and atrazine; methoxy substituted triazines, simeton, prometon and atraton; and methylmercapto substituted triazines, simetryne, prometryne and ametryne were used in this experiment in order to make clear their phytotoxicity for rice plant and barnyardgrass at the germinating stage. The results obtained were as follows: 1. There were apparent differences among these three substitutes in the toxicity both for rice plant and for barnyardgrass. Namely the toxicity for rice plant, listed in the increasing order, was methylmercapto-, methoxy-, and chloro-triazines. In the case of barnyardgrass, too, this tendency was the same, but the differences among the substituted radicals were slightly smaller than in rice plant. 2. The selectivity in toxicity, which is higher for barnyardgrass than for rice plant, was markedly different according to the substituted radicals: The methylmercapto triazines were extremely selective, the methoxy triazines slightly, and the chloro triazines little. 3. From the above-stated results, it was found that the methylmercapto triazines, simetryne, prometryne and ametryne were the most suitable herbicides for weed control in paddy fields.
