Biorational management of major pests of Kerala, Abelmoschus esculentus(L.) moench

Abstract

The study entitled “Biorational management of major pests of okra, Abelmoschus esculentus (L.) Moench” was carried out in the Instructional Farm, Karuvachery during two seasons viz., summer (January to May) and kharif (June to September) in the year 2022 to study the efficacy of different microbial agents, neem based and biorational insecticides against major pests of okra viz., okra shoot and fruit borer, aphids, jassids and leaf roller. Bioassay studies were conducted in the laboratory of Department of Entomology, College of Agriculture, Padanakkad during 2022-23 to evaluate the efficacy of microbial agents, neem based and biorational insecticides against aphids, jassids and leaf roller. Treatments were applied on test insects as three replications and the percentage mortality at fixed intervals was worked out. The field experiment was laid out in randomized block design (RBD) with nine treatments and three replications. The okra variety ‘Salkeerthi’ released by KAU was selected for the study. Treatments included were; T1: Bt formulation 2× 109 cfu/ml @ 10 ml/l of water; T2: Neem based formulation (Azadirachtin 1%) @ 2 ml/l of water; T3: Raksha (Neem oil, garlic, soap based formulation- KAU product) @ 6 g/l of water; T4: Emamectin benzoate 5% SG @ 0.4 g/l of water; T5: Pyridalyl 10 EC @ 1.5 ml/l of water; T6: Flonicamid 50 WG @ 0.6 g/l of water; T7: Spinosad 45 SC @ 0.4 ml/l of water; T8: Malathion 50 EC @ 2ml/l of water- Standard check; T9: Absolute control. Treatments were imposed at 30th, 45th and 65th day after sowing and observations were recorded at weekly intervals corresponding to standard weeks. The data were subjected to square root transformation and analysed using ANOVA in GRAPES (General R-shiny based Analysis Platform Empowered by Statistics) software. Bioassay studies indicated that highest percentage mortality of aphids, jassids and leaf roller were recorded in treatment T6 (Flonicamid 50 WG), T4 (Emamectin benzoate 5% SG) and T7 (Spinosad 45 SC) respectively after 24 hours of treatment application. Analysis of field experimental results showed that there is significant difference between the treatments in reducing the pest status of the crop as well as yield parameters of the crop. After three sprays, treatment T7 (Spinosad 45 SC @ 0.4 ml/l of water) at fortnightly intervals completely reduced shoot and fruit borer larvae in both summer and kharif seasons and leaf roller larvae in kharif season. Therefore, it was found that Spinosad 45 SC was effective in reducing the population of shoot and fruit borer and leaf roller as well as the percentage of shoot and fruit infested. During summer season, treatment T6 (Flonicamid 50 WG @ 0.6 g/l of water) was found to be the most effective treatment in reducing the nymphs and adults of aphids and their percentage shoot infestation in the vegetative phase of the crop. Treatment T4 (Emamectin benzoate 5% SG @ 0.4 g/l of water) and T2 (Azhadirachtin 1% @ 2 ml/l of water) were found effective in controlling the nymphs and adults of jassids in both summer and kharif seasons. T6 (Flonicamid 50 WG @ 0.6 g/l of water) also provided effective control of jassid population in the crop. Among the different treatments, maximum fruit length was recorded in T7 followed by T4 during both summer (17.13 and 15.50 cm) and kharif season (17.32 and 16.10 cm) respectively. Total yield was highest in T7 followed by T4 showing per plant yield of 384.87 and 360.53 g respectively during summer season and 502.65 and 479.47 g respectively during kharif season. Also, the same treatments recorded highest marketable yield of 369.79 and 339.75 g/plant respectively during summer season and 482.91 and 458.83 g/plant respectively during kharif season. During both seasons viz., Summer and kharif, highest benefit-cost ratio was recorded in T4 (2.73 and 3.62) and T7 (2.70 and 3.54) respectively. The results of the investigation clearly indicated that, along with then recommended package of practice, spraying of Spinosad 45 SC @ 0.4 ml/l of water provides effective control of okra shoot and fruit borer and leaf roller without reducing the marketability of the fruits. Spraying of Flonicamid 50 WG @ 0.6 g/l of water can be used to effectively control the sucking insects like aphids and also jassids. Emamectin benzoate 5% SG @ 0.4 g/l of water and Azadirachtin 1% @ 2 ml/l of water can be used to control nymphs and adults of jassids on okra