Abstract
Since 1999, control of Monochoria vaginais, Lindernia dubia, and Rotala indica with sulfonylurea (SU) herbicide-based mixtures was no longer satisfactory. Thus, the objectives of this study were to evaluate the response of M. vaginais, L. dubia, and R. indica resistant to SU herbicides and to determine effective herbicides by application timing for the control of resistant M. vaginais, L. dubia, and R. indica in wet-seeding and machine transplanting rice culture in Korea. The M. vaginais, L. dubia, and R. indica accessions collected from Jeonnam province in Korea were resistant to SU-herbicides such as bensulfuron-methyl, cyclosulfamuron, imazosulfuron, and pyrazosulfuron- ethyl. This means that the resistant weed biotypes were cross-resistant to the aforementioned herbicides. In wet-seeding rice culture, non-SU herbicides such as thiobencarb, fentrazamide, and oxadiargyl can be used to control the SU-resistant biotypes of M. vaginais, L. dubia, and R. indica when applied 5 days before seeding (DBS). Among the SU-herbicide based mixtures, pyrazosulfuron-ethyl plus pyrazolate plus simetryn and pyrazosulfuron-ethyl plus pyriminobac plus carfentrazon-ethyl can be used to control the SU-resistant biotypes of M. vaginais, L. dubia, and R. indica when applied 15 days after seeding (DAS). However, the SU-resistant M. vaginalis and R. indica were not controlled with pyrazosulfuron-ethyl plus molinate when applied 15 DAS. The SU-resistant L. dubia was not controlled with pyrazosulfuron-ethyl plus mefenacet plus dymuron when applied 10 DAS or pyrazosulfuron-ethyl plus molinate when applied 15 DAS. The SU-resistant biotypes of M. vaginais, L. dubia, and R. indica that survived from paddy fields treated with soil-applied herbicides could effectively be controlled by using mixtures of bentazon plus 2,4-D, bentazon plus MCPP-P, and bentazon plus MCPA. Rice plant injury was observed as a result of some herbicides used in this study 10 days after application (DAA), but the health of rice plant was restored 30 DAA. In machine transplanting the rice culture, non-SU herbicides, oxadiazon applied 2 days before transplanting (DBT) and benzobicyclon applied 5, 10, and 15 days after transplanting (DAT) can be used to control the SU-resistant biotypes of M. vaginalis, L. dubia, and R. indica. Several SU herbicide-based mixtures, pyrazosulfuron-ethyl plus mefenacet plus thiobencarb and pyrazosulfuron-ethyl plus pyrazolate plus simetryn applied 10 days after transplanting (DAT) or non-SU herbicide-based mixtures, pyrazolate plus butachlor, carfentrazon-ethyl plus thiobencarb applied 5 DAT, and thiobencarb plus simetryn applied 15 DAT can be used to control the SU-resistant biotypes of M. vaginalis, L. dubia, and R. indica. Rice plant injury was not observed as a result of the herbicides used in this study