Factors Affecting Herbicidal Activity of Imazosulfuron against Weeds in Paddy Fields.

Abstract

Factors affecting the herbicidal activity of imazosulfuron against weeds in paddy fields and movement of this herbicide in paddy soil were studied by bioassay method under greenhouse conditions. Reduction of more than 90% in dry weight was observed in Cyperus serotinus, Scirpus juncoides var. ohwianus and Echinochloa oryzicola treated with 90g a.i./ha of imazosulfuron for 1 day or more, 7 days or more and 14 days or more, respectively. Application of 90g a.i./ha at the sprouting stage of Sagittaria pygmaea suppressed the growth in dry weight irrespective of tuber size. However, at 3g a.i./ha growth of this plant sustained less reduction with increasing tuber size. Differences in flooding water depth and temperature had no appreciable influence on the herbicidal activity. Growth inhibition of S. juncoides var. ohwianus by pre-emergence or 1.5-leaf stage applications under nonleaching conditions was significantly higher than that under water leaching conditions. Under non-leaching condition, there was no remarkable difference in this inhibition between pre-emergence and 1.5-leaf stage applications, while under water leaching conditions the growth reduction with the latter application was significantly larger. Growth inhibition of S. juncoides var. ohwianus and S. pygmaea planted at a depth of 0.5cm and 2cm, respectively, was significantly higher than that planted deeper with the preemergence applications. With application at the 2-leaf stage of S. juncoides var. ohwianus, however, the difference in planting depth did not significantly affect the herbicidal activity. Bioassay method showed that movement in paddy soil, where the water leaching was conducted at the rate of 1.5cm/day from the 4cm flooding water depth following application of 150g a.i./ha, was limited to within 2cm of the soil layer under the soil surface.