Bioefficacy, phytotoxicity, safety to natural enemies and residue dynamics of imidacloprid 70 WG in okra (Abelmoschus esculenta (L) Moench) under open field conditions

Abstract

Sucking pests are a major menace and cause considerable damage to okra cultivation in India. Field experiments were carried out to evaluate the bioefficacy, phytotoxicity, safety and residue dynamics of imidacloprid in okra (Abelmoschus esculenta (L.) Moench). Out of the four doses tested viz., imidacloprid 70 WG at 17, 21, 24.5 and 35 g a.i ha−1, the 24.5 g a.i ha−1 dose was equally effective in controlling sucking pests viz., aphids, Aphis gossypii (Glover), leafhoppers, Amrasca biguttula biguttula Ishida and thrips, Thrips tabaci Lindeman as the highest dose of 35 g a.i. ha−1 under open field conditions, reducing pest populations by >80% when compared to untreated controls after two rounds of foliar application at an interval of 15 days. The chemical did not cause any phytotoxic symptoms even at 49 g a.i ha−1. It was also found to be safer to the natural enemies (spiders and coccinellids) prevailing in the okra ecosystem when compared with the higher dose of 35 g a.i. ha−1. Initial deposits of imidacloprid 70 WG at 24.5 and 49 g a.i. ha−1 in okra fruits were 0.15 and 0.26 μg g−1, respectively, and the residues fell to the Below Detection Limit (BDL) of 0.01 μg g−1 five days after application at both the doses. Imidacloprid residue dissipation followed first order kinetics with half-lives ranging between 1.04 and 1.13 days for the above two doses, respectively. The residues dissipated to below the MRL of 0.7 μg g−1 on the same day. These findings can be utilized in deciding the spray schedule and for safety evaluation of imidacloprid in okra crops.