Persistence of two insecticides, Bifenthrin [(2-methyl[1,1-biphenyl]-3-yl)-methyl-3- (2-chloro-3,3,3-trifluoro-1-propenyl)-2,2-dimethyl cyclopropanecarboxylate] and Chlorpyrifos [O,O-diethyl O-(3,5,6-trichloro-2-pyridinyl)phosphorothioate] were studied under field conditions. Chlorpyrifos is one of the pesticides used in nursery stock quarantine treatment of Japanese beetles grubs in balled and burlapped (B&B) nursery soil. Japanese Beetles (Popillia japonica Newman) cause large-scale damage to horticultural and nursery crops. Chlorpyrifos is also one of the most common insecticides used in the dip treatment option for controlling soil-borne Japanese beetle grubs; the use of this treatment option meets the nursery quarantine requirements of the United States Domestic Japanese Beetle Harmonization Plan. If chlorpyrifos becomes unavailable in the future, there would be limited insecticide alternatives for the dip treatment. Therefore, there is a need to study the persistence of other pesticides such as bifenthrin as a potential chlorpyrifos replacement for the treatment of the Japanese beetle. The specific objectives of the study were: (1) to evaluate the residue levels of chlorpyrifos in the B&B soils at 1, 2 and 4 months after chemical treatment; (2) to evaluate the residue levels of bifenthrin in the B&B soils at 1, 2 and 4 months after treatment; (3) to compare the residue levels of the pesticides as a function of the dip and drench treatments. Two post-harvest quarantine treatment techniques, consisting of dip and drench treatments were used to apply chlorpyrifos and bifenthrin to the (B&B) stock at field application rates. Soil samples were taken from the B&B stock at 1.0, 2.0 and 4.0 months after pesticide treatment for residue analysis. The pesticides were extracted with methylene chloride and acetone 1:1(v/v) and analyzed with a Gas Chromatograph. Chlorpyrifos and bifenthrin were present in the samples analyzed except control; with the highest concentrations recovered from the one-month soil samples; chlorpyrifos 167.53 mg/L and bifenthrin 20.76 mg/L.