Influence of time and duration of drainage after sprouting of direct-seeded paddy rice on the herbicidal action of pyrazolate.

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In order to establish an efficient method of weed control in direct-seeded paddy fields under flooded conditions, we examined the influence of the time and duration of the drainage treatment after rice sprouting on the herbicidal action of pyrazolate in lowland weeds (Fig. 1).The results obtained are as follows;(1) Herbicidal effect of pyrazolate on Echinochloa oryzicola VASING. varied widely depending upon the time and duration of the drainage. Particularly, prolonged drainage implemented one day after the application decreased remarkably the control efficacy (Table 1, Fig. 2).(2) Even in the plot in which the control efficacy was the lowest, the concentration of the active ingredient, 4-(2, 4-dichlorobenzoyl)-1, 3-dimethyl-5-hydroxypyrazole, in the paddy water supplied after the drainage period exceeded 0.3ppm. This concentration may be high enough to control E. oryzicola if the chemical is applied at the growth stage of the plant susceptible to pyrazolate (Fig. 3).(3) The above results suggest that the reduced control efficacy of pyrazolate can be attributed to the growth of E. oryzicola to the stage resistant to pyrazolate during the drainage period when the herbicidal activity is suppressed. Therefore the prolonged drainage implemented immediately after the application of pyrazolate in warmer regions in Japan may reduce the herbicidal efficacy against E. oryzicola which emerges mostly in the early period after puddling.
日本雑草学会の論文