数種α-クロロアセトアニリド系除草剤の移植水稲薬害に及ぼす湛水深の影響

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Effect of application of butachlor [N-butoxymethyl-α-chloro-2', 6'-diethylacetanilide] , pretilachlor [α-chloro-2', 6'-diethyl-N- (2-propoxyethyl) acetanilide] and NSK-850 [α-chloro-N-(3-methoxy-2-thienyl) methyl-2', 6'-dimethylacetanilide] herbicides on the growth of transplanted rice (cv. Akinishiki, 2 leaf stage) cultivated at different depths (1, 4 and 8 cm) of flooding water was examined by pot tests in a greenhouse. Inhibitory effect on plant height and dry weight of shoots of rice plants by butachlor (15 g/a), pretilachlor (10 g/a) and NSK-850 (5 g/a) decreased with the increase of the depth of the flooding water (Fig. 1). These results could not be explained by the difference in herbicide sensitivity of rice plants in relation to the changes in the depth of flooding water, because rice plants grew taller, the dry weight of their shoots decreased and thus they were likely to be come more sensitive to herbicides with the increase of the depth of flooding water (Fig. 2). Therefore, it was suggested that other factors such as the role of the plant parts related to the absorption of the herbicides and behavior of the herbicides in soil and water were mainly involved in the above-mentioned phenomena. Plant parts related to the absorption of butachlor, pretilachlor and NSK -850 were examined by application of the chemicals to leaf blades, shoots (basal parts) and roots of rice plants. Since the chemicals inhibited the growth of rice plants most strongly by root application, it was concluded that these herbicides were absorbed mainly through roots in rice plants (Fig. 3). Time course of butachlor, pretilachlor and NSK-850 concentrations in flooding water and soil was monitored by HPLC analyses during 300 hr following the treatment. In all cases, the concentrations of the herbicides in flooding water decreased with the increase of the depth of flooding water, and reached maximum values shortly after treatment. Similar results were obtained for the concentrations of the herbicides in soil, but maximum values were observed later than in the case of flooding water. The results obtained suggested that the depth of flooding water affected the rice phytotoxicity of theseα-chloroacetanilide herbicides, i.e. butachlor, pretilachlor and NSK-850. This assumption was based on the fact that since the herbicide concentrations in water and soil in the vicinity of the main parts of the plant related to the absorption of the chemicals increased shortly after application when the depth of flooding water decreased, a larger amount of the chemicals was likely to be absorbed.
日本雑草学会の論文
1990-07-27

数種α-クロロアセトアニリド系除草剤の移植水稲薬害に及ぼす湛水深の影響

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