Effect of Dymron on the Selectivity Between Rice and Barnyardgrass Treated with Herbicide Mixture Including Dymron

The effect of dymron on the selectivity between rice and barnyardgrass treated with a herbicide mixture including dymron was evaluated under greenhouse condition. Pyrazosulfuron-ethyl, cinosulfuron, and KSC-13906 represented phytotoxicity on rice seedlings during 5 to 15 days after treatment (DAT), however, this phytotoxicity was recovered after 20 DAT. Addition of dymron decreased phytotoxicity of KSC-13906, pyrazosulfuron-ethyl, and pretilachlor against rice seedlings, however, it showed even or incremental rice phytotoxicity against mefenacet and molinate. The descending order of safening effects of dymron toward several herbicides on the rice seedlings was that of pretilachlor, KSC-13906, pyrazosulfuron-ethyl. Also, herbicidal activities of KSC-13906, pyrazosulfuron-ethyl, and pretilachlor to the barnyardgrass were diminished as combination with dymron. Among the stereoisomers of demethyldymron tested, R-form isomer showed superior safening activity to S-form compound. However, the mixture of R- and S-demethyldymron showed the highest safening activity against 10 g/ha of KSC-13906 to the rice seedlings. The safening mode of dymron action might be related to the acetolactate synthase because the inhibition rate of pyrazosulfuron-ethyl and KSC-13906 was slightly reduced by addition of dymron and coincided with the patterns of in vivo results