MSc

The present study was undertaken to screen new synthetic insecticide molecules and neem based insecticides against two major pests of okra in the laboratory and to evaluate the bioefficacy of promising insecticides in the field against the major pests and to assess their toxicity to natural enemies. The insecticides selected for the laboratory study were neem based insecticides viz., neemAzal T/S (0.4%), neem oil (2%) and NSKE (4%) and newer synthetic insecticides viz., thiamethoxam (0.02%), imidacloprid (0.02%), fenvalerate (0.015%), fluvalinate (0.015%), beta-cyfluthrin (0.04%), lambda-cyhalothrin (0.02%), profenofos (0.05%), acephate (0.05%) and triazophos (0.05%). Dimethoate (0.05%) and quinalphos (0.05%) were used as the checks. The leafhopper (A. biguttula biguttula) and the leafroller (S. derogata) were the test insects selected for the laboratory studies. The test insects of uniform stage were released on the treated leaves of okra at intervals of 1, 3, 6, 9, 12 and 15 days after treatment and the mortality was recorded at 24 hours after release. Thiamethoxam (0.02%), imidacloprid (0.02%), and profenofos (0.05%) proved more effective against the okra leafhopper (A. biguttula biguttula). Beta-cyfluthrin (0.04%), profenofos (0.05%), and dimethoate (0.05%) were found superior against the leafroller (S. derogata).
The promising treatments in the laboratory study were selected for field evaluation along with an additional treatment of seed dressing using imidacloprid (Gaucho 70 WS) @ 10g kg-1 seed. Foliar application of insecticides were applied at 30th day after sowing in synchronization with the first appearance of the pest and a second at 45th day after sowing. Seed treatment with imidacloprid @10g /kg seed protected the crop from leafhopper A. biguttula biguttula, aphid A. gossypii, whitefly B. tabaci and leaf roller S. derogata upto seven weeks, did not disturb the natural enemy population and resulted in the highest yield. The highest return of Rs. 2.06 for every one rupee invested was recorded.
Foliar application of thiamethoxam (0.02%), imidacloprid (0.02%) and profenofos(0.05%) gave greater reduction of populations in leafhopper A. biguttula biguttula, aphid A. gossypii, whitefly B. tabaci. Profenofos (0.05%) and quinalphos (0.05%) were the most effective against the larval population of leafroller. The chemicals found superior against the shoot and fruit borer E. vitella were profenofos (0.05%), lambda-cyhalothrin (0.02%) and beta-cyfluthrin (0.04%). Except neemAzal T/S all the other insecticides resulted in immediate suppression of the natural enemy population such as coccinellid, syrphid and spider. However, lower toxicity of these insecticides was observed against the braconid population. Among the treatments, the neonicotinoids viz., imidacloprid and thiamethoxam and the synthetic pyrethroid, fenvalerate were found less toxic while the organophosphate insecticides viz., profenofos, dimethoate and quinalphos were more toxic to coccinellid, syrphid, spider and braconid population upto ten days after spraying. Foliar applications of thiamethoxam (0.02%) and imidacloprid (0.02%) were proved better against sucking pest complex and were less toxic to natural enemy population in okra.
However, the safety of these chemicals in terms of the persistence of residues in the fruits may be further studied before making recommendation in Integrated Pest Management (IPM) programme.