PHYSICOCHEMICAL PROPERTIES OF FORMULATIONS WITH RESPECT TO SOME SPECIFIC BIOLOGICAL EFFECTS, AND METHODS FOR THEIR DETERMINATION

Abstract This paper deals with two controlled release formulations, an edifenphos microcapsule suspension and a FOE 1976 granular formulation, which are to be used to control Pyricularia oryzae on rice plants and weeds in paddy fields respectively. To improve efficacy of edifenphos capsule suspension, which was originally inferior to its emulsifiable concentrates, a surfactant was added either to the aqueous medium or the core. With a surfactant added to the medium, the amount of liberated edifenphos was increased to the saturation amount of solubilization. From encapsulated mixture of edifenphos/surfactant, these two components were concomitantly released at almost equal ratio to that of original mixture. In addition, the amount of released edifenphos was greatly increased. However, even by these techniques, efficacy of encapsulated edifenphos could not be improved sufficiently. On the basis of kinetics of the herbicide release to water from FOE 1976 granular formulations, it was concluded that the herbicide was liberated quite rapidly at the very beginning, in the case of the granular formulations containing a surfactant. This unsteady release is inferred to have been caused by the immediate solubilization of herbicide with the surfactant. In controlling the paddy field weeds which germinate gradually, the slow and moderate release of herbicide were more efficient than the rapid liberation.