Herbicidal Selectivity of Foliar-Applied Simetryne: Its Absorption, Translocation and Metabolism in Gramineous Plants

Abstract

The selectivity pattern of foliar-applied simetryne [2, 4-bis (ethylamino)-6-(methylthio)-s-triazine] was studied in six gramineous plant species. Their tolerance to simetryne could be described by the following sequence: rice (Oryza sativa L.)> wheat (Triticum aestivum L.)>corn (Zea mays L.)>barnyardgrass (Echinochloa crus-galli Beauv.)>large crabgrass (Digitaria adscendens Henr.)>finger millet (Eleusine coracana Gaertn.). In order to clarify the selectivity mechanism of simetryne, its absorption, translocation and metabolism in rice (tolerant) and barnyardgrass (susceptible) were investigated. The rates of absorption of ¹⁴C-simetryne by shoots were much higher in barnyardgrass than in rice, but few differences were observed in translocation and degradation rates. The main metabolic pathway, however, was remarkably different. The investigation on absorption of ¹⁴C-simetryne was then further extended to six gramineous plant species. The rates of absorption were remarkably different among these plants, susceptible plants exhibiting much higher rates than tolerant species. It was concluded that the selectivity of foliar-applied simetryne was mainly due to species related differences in the rates of absorption, and in metabolic pathways.