OBJECTIVES: A field experiment was conducted at Agricultural Research Station for irrigated crops at Thasara, Anand Agricultural University, Anand, to study the dissipation and risk assessment of β-cyfluthrin and imidacloprid as combination product in/on chickpea. 

MATERIALS AND METHODS: Solomon 300 OD comprising 9 per cent β-cyfluthrin and 21 per cent imidacloprid was foliar sprayed at the doses of 18 + 42g a.i. ha^-1 (standard dose) and 36 + 84g a.i. ha^-1 (double dose). Totally three sprays were made at an interval of 1 week starting from fruiting stage. 

RESULTS AND DISCUSSIONS: The residues of β-cyfluthrin estimated using gas chromatograph with electron capture detector (GC-ECD) showed an initial deposit of 0.16 and 0.27 μg g^-1 in standard and double doses, respectively. The residues for corresponding doses persisted till 7th and 10th day after application and reached below determination level of 0.01μg g^-1 on the 10th and 15th day, respectively. Imidacloprid was estimated using high performance liquid chromatography (HPLC) and showed initial deposits of 1.22 and 2.7 μg g^-1 in standard and double doses, respectively. Its levels reached below the determination level (0.01 μg g^-1) on the 15th day in green pods. Statistical analysis of dissipation kinetics showed that β-cyfluthrin followed zero-order kinetics in standard dose with half-life of 7.27 days. In double dose, the dissipation kinetics followed first-order kinetics with half-life of 9 days. Imidacloprid followed first-order kinetics in both the doses with half-life of 6.7 and 7.7 days. 

CONCLUSIONS: A pre-harvest interval (PHI) of 15 days is suggested. Theoretical risk assessment calculated as hazard quotient was less than 1, rendering the use of combination product as safe-provided proper PHI is followed.