I. Chemical and biological field life of various synthetic pyrethroid formulations

Abstract

Abstract The field life for contact activity of three synthetic pyrethroids against grass grub beetles has been measured in laboratory bioassays, and compared with the chemical residue levels remaining on the sprayed foliage. In one trial, two emulsifiable concentrate (EC) formulations of cypermethrin and a microencapsulated permethrin formulation, each applied to pasture at 0.1 kg/ha, were highly active for up to 6 days, while an EC formulation of permethrin, at the same rate, lost activity significantly faster (P <0.05). Fenvalerate EC, at the same rate, was significantly (P >0.01) less active than the other two chemicals, even on the day of application. In a second trial, cypermethrin EC applied at 0.1 kg/ha again retained a good activity after 4 days, but microencapsulated permethrin at 0.05 and 0.1 kg/ha both lost activity faster (P <0.05). Cypermethrin EC at 0.05 kg/ha also seemed to lose activity faster than when applied at the higher rate. An ultra-low volume application of cypermethrin was inactive. Chemical residue analysis showed this to be caused by a very low insecticide deposit on the foliage. A third trial showed that applications of dust formulations of cypermethrin lost activity after 1 day of weathering. Again the residue levels of insecticide on the foliage were low.