Controlled Release Study on Microencapsulated Mixture of Fipronil and Chlorpyrifos for the Management of White Grubs (Holotrichia parallela) in Peanuts (Arachis hypogaea L.)

This study was conducted to determine the release dynamics of a microencapsulated mixture of fipronil and chlorpyrifos in peanut fields and its efficacy against white grubs. The results indicated that microencapsulation significantly stabilized this mixture against degradation in the environment so that a single dose of this microencapsulated formulation applied through seed treatment effectively controlled white grubs throughout the entire growing season. During the experimental course, the concentration of chlorpyrifos in the soil with the microencapsulated formulation was 13.6 ± 9.9 (n = 6) times that of the conventional formulation, and the concentration of fipronil was at least 2.2 times that of the conventional formulation in the soil and peanut roots. However, the residue risks of chlorpyrifos and fipronil in the kernels were different. At harvest, there was a low risk that the residual chlorpyrifos in the kernels exceeded the MRLs (maximum residue limit). In contrast, the amount of residual fipronil in some kernel samples reached the statutory MRL set by the European Union, which suggested that a higher application rate or the repeated application of the microencapsulated fipronil formulation would not be acceptable.