Effect of vegetation on the longevity, mobility and activity of fipronil applied at the termiticidal rate in laboratory soil columns.

BACKGROUND Termiticides are applied at concentrations much higher than those used in agricultural settings. The longevity of fipronil has not yet been examined at the rates used for termite control, nor has the compound's movement in the soil been addressed. RESULTS Fipronil was detected in the eluates of treated soil cones, increasing initially and then decreasing to a steady concentration of about 1 microg mL(-1). In larger PVC pipe plots, fipronil in the top treated soil depth (0-7.5 cm) dissipated more rapidly (half-life of 11-13 months) than in treated soil at the next treated depth (7.5-15 cm; half-life of 20-29 months). The presence of vegetation had no significant effect on the mobility, longevity or movement into untreated depths. Treated soil remained toxic to termites throughout the duration of the study. Fipronil moved into the 15-22.5 cm soil depth in sufficient concentration to cause 100% mortality to eastern subterranean termites in 3 day bioassays. CONCLUSION Fipronil remains in treated soil at levels toxic to termites for at least 30 months. Movement of the active ingredient was observed in sufficient amounts to kill termites in non-treated soil directly below the treated soil.