Sulfonylurea-resistant biotypes of Monochoria vaginalis in paddy fields of Akita and Ibaraki Prefectures, eastern Japan.

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Susceptibility of Monochoria vaginalis to bensulfuron-methyl was investigated in seeds collected in fifteen paddy fields in three Prefectures, namely Akita, Ibaraki and Gifu, in eastern Japan, where the species had been growing profusely. The susceptibility was assayed based on the effect of the application of bensulfuron-methyl on the seminal root length in agar media. M. vaginalis seedlings which germinated from seeds collected in a paddy field in Kyowa town, Akita Prefecture, and in three paddy fields in Miho village, Ibaraki Prefecture, were found to be resistant to bensulfron-methyl (Tables 1, 3, 6, Fig. 1), where a combination of sulfonylurea herbicides had been applied during more than three consecutive years (Table 4). However, the resistant biotype of M. vaginalis was controlled by mefenaset and pretilachlor in agar culture medium test (Table 5). The biotype of M. vaginalis resistant to bensulfuron-methyl displayed a cross-resistance to other sulfonylurea herbicides in Wagner pot experiments (Table 6). The application of a combination of sulfonylurea herbicides including mefenacet, pretilachlor or benthiocarb and pyrazolate enabled to control the sulfonylurea-resistant biotype of M. vaginalis effectively, when the herbicides were applied at the 1st leaf stage of the species in Wagner pot experiments (Table 6).
日本雑草学会の論文