Abstract
NSK-850, α-chloro-N-(3-methoxy-2-thienyl) methyl-2′, 6′-dimethylacetanilide, was studied for its herbicidal activity, selectivity and behavior in soil, including residual activity and mobility. The results are summarized as follows:
1. In a pot test carried out in a green house, NSK-850 effectively controlled Echinochloa oryzicola VASING., Cyperus difformis L., Rotala indica (WILLD.) KOEHNE, Scirpus juncoides ROXB. subsp. juncoides ROXB. and Cyperus serotinus ROTTB. at a dose of 1g a. i./a by pre-emergence treatment. The herbicide inhibited the growth of directly sown rice plants at a dose of 0.125g a. i./a, while transplanted rice plants were not affected even at a dose of 2g a. i./a (Table 4). NSK-850 showed a stronger herbicidal activity than pretilachlor against Echinochloa oryzicola at the 2-and 3-leaf stages, when the two herbicides were applied at doses at which they exhibited almost equal activities against the weed at the 1-leaf stage (Fig. 1). Activities of the herbicides decreased with the decrease of the depth of flooding water (Fig. 2). Echinochloa oryzicola once treated with 2g a. i./a NSK-850 at the 2-leaf stage slightly recovered from the inhibition 27 days after treatment. However, in the case of pretilachlor, recovery from the inhibition was observed 17 days after the plants had been treated with the herbicide at a dose of 4g a. i./a (Fig. 3).
2. In a field test, NSK-850 effectively controlled Echinochloa oryzicola, from the pre-emergence to the 2-leaf stages, at a dose as low as 3g a. i./a without adverse effect on transplanted rice plants. However, the control of Scirpus juncoides or Cyperus serotinus was not adequate (Table 5).
3. NSK-850 applied to flooded soil remained active for 30 days at a low temperature (5°C), whereas it lost its activity rapidly under high temperature conditions (30°C) (Fig. 4). When NSK-850 and pretilachlor were applied at doses at which they exhibited almost equal activity against Echinochloa oryzicola, 1 and 2g a. i./g respectively, the latter herbicide showed a slightly longer residual activity than the former. NSK-850 was less mobile than pretilachlor in the soils tested. Relative mobility of NSK-850 in the soils decreased in the order of sandy loam soil>loam soil>clay loam soil (Table 6).
