MSc

A study on “Insecticide mixtures for the management of pest complex in brinjal” aims to evaluate the efficacy of insecticide mixtures having component molecules of different mode of action against pests of brinjal and to find out the harvest time residues in fruits. Experiment was conducted at Instructional Farm, College of Agriculture, Vellayani, Thiruvananthapuram during 2018-19.
Preliminary experiment was carried out in CRD to evaluate the efficacy of insecticide mixtures against grub and adults of epilachna beetle, Epilachna vigintioctopunctata, and nymphs of mealy bug, Coccidohystrix insolita. Insecticide mixtures viz. pyriproxyfen 5% + fenpropathrin 15% EC @ 25+75g a.i ha-1, fipronil 40% + imidacloprid 40% WG @ 175+175g a.i ha-1, thiamethoxam 12.6% + lambda cyhalothrin 9.5% ZC @ 27.5g a.i ha-1, betacyfluthrin 8.91% + imidacloprid 19.81%w/w @ 15.75+36.7g a.i ha-1, flubendiamide 19.92% w/w + thiacloprid 19.92% w/w @ 48+48g a.i ha-1, cypermethrin 3% + quinalphos 20% EC @ 30 + 200 g a.i ha-1 , deltamethrin 1% + triazophos 35% EC @ 10+350g a.i ha-1 were selected for the study. The recommended dose of these mixtures were prepared in aqueous solution and bioassay was done using 3rd instar grubs and adults of epilachna and 3rd instar nymphs of mealy bug.
Results of the laboratory experiment revealed, cent per cent mortality of epilachna adults which were treated with betacyfluthrin 8.91% + imidacloprid 19.81% w/w @ 15.75+36.7g a.i ha-1, cypermethrin 3% + quinalphos 20% EC @ 30 + 200 g a.i ha-1 and fipronil 40% + imidacloprid 40% WG @ 175+175g a.i ha-1 after 96 h of treatment. Similar results were obtained in the mortality of epilachna grub after 72 h of treatment. Cent per cent mortality of mealy bug was observed when treated with betacyfluthrin 8.91% + imidacloprid 19.81% w/w @ 15.75+36.7g a.i ha-1, fipronil 40% + imidacloprid 40% WG @ 175+175g a.i ha-1 , cypermethrin 3% + quinalphos 20% EC @ 30 + 200 g a.i ha-1 and deltamethrin 1% + triazophos 35% EC @ 10+350g a.i ha-1 after 120 h of treatment. Based on the laboratory results three insecticide mixtures were selected for field study viz., betacyfluthrin 8.91% + imidacloprid 19.81% w/w @ 15.75+36.7g a.i ha-1, cypermethrin 3% + quinalphos 20% EC @ 30 + 200 g a.i ha-1 and fipronil 40% + imidacloprid 40% WG @ 175+175g a.i ha-1 .
Field experiment was laid out in RBD at Instructional Farm, College of Agriculture, Vellayani, Thiruvananthapuram during summer 2018-19. Major pests documented in experimental field were whitefly, leafhopper, mealybug and shoot and fruit borer. Less incidence of whiteflies was observed in cypermethrin 3 % + quinalphos 20 % EC @ 30 + 200 g a.i ha-1 (0.72 plant-1) treated plants on fifteenth day after spraying followed by fipronil 40 % + imidacloprid 40 % WG @ 175+175g a.i ha-1 (1.78 plant-1) and betacyfluthrin 8.91 % + imidacloprid 19.81% w/w @ 15.75+36.7g a.i ha-1 (1.92 plant-1). The Lowest population of leaf hopper was observed in plants treated with cypermethrin 3% + quinalphos 20 % EC @ 30 + 200 g a.i ha-1 (0.32 plant-1) on fifteenth day after spraying followed by fipronil 40 % + imidacloprid 40 % WG @ 175+175g a.i ha-1 (0.96 plant-1) and betacyfluthrin 8.91% + imidacloprid 19.81 % w/w @ 15.75+36.7g a.i ha-1 (1.04 plant-1). Cypermethrin 3% + quinalphos 20 % EC @ 30 + 200 g a.i ha-1 was found to be superior over other treatments, in managing the population of mealy bug (1.71 plant-1) on fifteen days after treatment and was found on par with betacyfluthrin 8.91 % + imidacloprid 19.81 % w/w @ 15.75+36.7g a.i ha-1 (4.08 plant-1). Low percentage of shoot borer damage was recorded in plants treated with betacyfluthrin 8.91 % + imidacloprid 19.81 % w/w @ 15.75+36.7g a.i ha-1 (1.74%) on 30 DAS and was found on par with cypermethrin 3% + quinalphos 20 % EC @ 30 + 200 g a.i ha-1 (1.82 %) and fipronil 40 % + imidacloprid 40% WG @ 175+175g a.i ha-1 (1.93% ). Cypermethrin 3% + quinalphos 20 % EC @ 30 + 200 g a.i ha-1 treated plants showed the lowest fruit damage (8.85%) on 30 days after spraying followed by betacyfluthrin 8.91 % + imidacloprid 19.81% w/w @ 15.75+36.7g a.i ha-1 (10.34%).
Betacyfluthrin 8.91 % + imidacloprid 19.81% w/w @ 15.75+36.7g a.i ha-1 treated plots recorded maximum yield (1.72 kg plant-1) followed by fipronil 40% + imidacloprid 40% WG @ 175+175g a.i ha-1 (1.64 kg plant-1) and cypermethrin 3 % + quinalphos 20 % EC @ 30 + 200 g a.i ha-1 (1.42 kg plant-1).
The harvest time residues of these effective insecticide mixtures were studied and results revealed that all three effective insecticide mixtures were below limit of quantification (LOQ).
The results of present study revealed that insecticide mixtures viz., betacyfluthrin 8.91% + imidacloprid 19.81% w/w @ 15.75+36.7g a.i ha-1, cypermethrin 3%+ quinalphos 20% EC @ 30 + 200 g a.i ha-1 and fipronil 40 % + imidacloprid 40 % WG @ 175+175g a.i ha-1 could effectively manage pest complex in brinjal.