Persistence and residual toxicity of some insecticides against Helicoverpa armigera on field pea

The persistence and residual toxicity of monocrotophos, endosulfan, quinalphos, cypermethrin, deltamethrin, fenvalerate and fluvalinate at effective concentrations viz., 0.04, 0.07, 0.05, 0.006, 0.002, 0.06 and 0.008 and 0.006 per cent, respectively in field pea were studied against 5 to 6 day old larvae ofHelicoverpa armigera (Hubner). The average PT 1, 3, 7, 10 and 14 days of application continuously in two seasons during the experimentation for cypermethrin, endosulfan, fenvalerate, quinalphos, monocrotophos, deltamethrin and fluvalinate were 718.68, 686.00, 681.32, 644.00, 639.25, 620.68 and 578.68, respectively. Evidently cypermethrin was found to be the most persistent and toxicity (RPT) calculated by taking the PT value of fluvalinate as standard, cypermethrin, endosulfan, fenvalerate, quinalphos, monocrotophos and deltamethrin were 1.24, 1.19. 1.18, 1.11, 1.10 and 1.07, times as persistent as fluvalinate, respectively. The synthetic pyrethroids had high initial check over H. arimigera larvae in comparison with conventional insecticides but toxicity was on decline after 3 days. Residual toxicity decreased with lapse of time. Residual toxicity of cypermethrin, fenvalerate, endosulfan, quinalphos and monocrotophos declined gradually and provided long time protection, hence their application should be repeated after 15 days. Deltamethrin and fluvalinate showed sharp decline in residual toxicity 3 days after application suggesting reapplication at 10 days interval.