Changes in concentrations of active ingredients of a flowable and granules consisting of a combination of pyributicarb, bromobutide and benzofenap in water of paddy [Oryza sativa] fields

Changes in the concentrations of active ingredients of a flowable (TSM-612), a new type of directly-applicable formulation of paddy field herbicide, and conventional granules (TSM-344H) consisting of a combination of pyributicarb, bromobutide and benzofenap in the water of paddy fields were investigated. In the case of TSM-344H granules, the concentrations of the three active ingredients increased slowly during the day of application, and the concentrations of pyributicarb and benzofenap were slightly higher than the level of water solubility. On the day following the application, the concentrations of all the active ingredients decreased below the level of water solubility, and thereafter, the concentrations decreased gradually with the lapse of time. On the other hand, in the case of the TSM-612 flowable, the concentrations of all the active ingredients were higher than those of the TSM-344H granules immediately after the application, and were maximum within 6 hours after the application. Moreover, the maximum concentrations of pyributicarb and benzofenap were much higher than the level of water solubility. Concentrations of the three active ingredients, however, decreased rapidly until the second day after the application, and then, gradually as in the case of the granules. The difference in the concentrations of the active ingredients between the TSM-612 flowable and TSM-344H granules on the day of application may account for the fact that the directly-applicable flowable showed higher diffusion properties in flooding water and a stronger herbicidal activity than the granules in paddy fields when the water solubility of the active ingredients was low. In addition, since the concentrations of the active ingredients of the granules and flowable decreased in almost the same way two days after the application, the degree of run-off the three active ingredients of the flowable from the paddy fields was as low as that of the granules under standard conditions employed to avoid water drainage after the application of the herbicide for three days.