Bio-efficacy of Insecticides against Pod Borers Infesting Cowpea [Vigna unguiculata (L.) Walp.]

Nine insecticides were evaluated on cowpea against pod borers (Maruca vitrata and Heliocverpa armigera) during kharif 2017 & 2018 and results revealed that flubendiamide 0.02% (0.16 larva/plant), fipronil 0.01% (0.35 larva/plant) and chlorantraniliprole 0.0056% (1.18 larva/plant) were found highly effective insecticides whereas, spinosad 0.009% (1.24 larva/plant), profenophos 0.05% (1.40 larva/plant), novaluron 0.01% (1.43 larva/plant) and emamectin benzoate 0.0025% (1.48 larva/plant) were found moderately effective insecticides against M. vitrata. Treatments of chlorantraniliprole 0.0056% (0.19 larva/plant), flubendiamide 0.02% (0.27 larva/plant) and fipronil 0.01% (0.30 larva/plant) were found highly effective insecticides whereas, spinosad 0.009% (0.91 larva/plant), profenophos 0.05% (1.06 larva/plant), novaluron 0.01% (1.11 larva/plant) and emamectin benzoate 0.0025% (1.11 larva/plant) were found moderately effective insecticides against H. armigera. Treatments of acephate 0.075% and thiamethoxam 0.005% were found least effective insecticides against pod borers.


INTRODUCTION
The larvae of M. vitrata web the flowers or inflorescence with the adjacent leaves and pods, feed from inside the webbed mass which protects them from the natural enemies and adverse natural conditions. The later instar larvae bore in to the pods and feed on developing grains. Excretory material is often seen at the entrance of bore holes. The larvae of H. armigera also cause extensive damage by feeding on various plant parts viz., leaves, buds, flowers and pods of cowpea. Young larvae feed on the leaves, while fully grown larvae feed on the pods by thrusting its head into the pod and keeping remaining body outside. The avoidable losses in yield due to insect pests have been recorded in the range of 66 to 100 per cent in cowpea (Pandey et.al., 1991). Thus, considering the damage and yield loss due to pod borers in cowpea, it is necessary to evaluate bio-efficacy of various new insecticides against pod borers.

MATERIALS AND METHODS
An experiment was conducted on management of pod borers (M. vitrata and H. armigera) infesting cowpea at College of Agriculture, Navsari Agricultural University, Campus Bharuch (Gujarat) during kharif 2017 and 2018. The experiment was carried out in randomized block design with 10 treatments. The observations were recorded from plot size; gross 2.25m x 2.00m and net 1.35m x 1.60m. Gujarat cowpea-4 variety was sown at a distance of 45cm × 20cm and crop was raised successfully by adopting recommended agronomical practices. Three spray of insecticides were given at an interval of 10 days. The first spray was given on appearance of pests and second and third spray was given at an interval of 10 days from first spray. The observations on larval populations of M. vitrata and H. armigera were recorded from randomly selected five plants from each treatment by counting numbers of larva/plant before first spray as well as 3, 7 and 10 day(s) after each spray. The data on mean larval population were subjected to ANOVA after transforming into √ transformation.

RESULTS AND DISCUSSION Spotted pod borer, Maruca vitrata
The data on larval population pooled over sprays and years are presented in Table 1 and depicted in Fig. 1. The pooled data of before spray of two years were not significantly differed indicating homogenous distribution of larval population (Column 3). All the insecticidal treatments recorded significantly lower larval population than control.
The higher efficacay of flubendiamide against M. vitrata was reported by various workers viz., Patil et al. (2008), Ameta et al. (2011), Joshi (2011), Dey et al. (2012 and Subhasree and Mathew (2014). The higher efficacy of fipronil was reported by Chandrayudu et al. (2006) and Singh and Singh (2015). The higher efficacy of spinosad was reported by Lakshmi et al. (2002), Srihari andPatnaik (2006) and Bairwa and Singh (2015). The good efficacy of emamectin benzoate was reported by Prudhvi (2007). The effcetviness of profenophos was reported by Prajapati et al. (2009) and Umbarkar and Parsana (2014). Thus results of present investigation is more or less in conformity with the work done by previous workers.

Pod borer, Helicoverpa armigera
The data on larval population pooled over sprays and years are presented in Table 2 and depicted in Fig. 2. The pooled data of before spray of two years were not significantly differed hence homogenous distribution of larval population in different plots under different treatment (Column 3). All the insecticidal treatments recorded significantly lower larval population than control.
Thus, the results revealed that chlorantraniliprole 0.0056%, flubendiamide 0.02% and fipronil 0.01% were found most effective insecticides for management of H. armigera followed by spinosad 0.009%. Treatments of Profenophos 0.05%, emamectin benzoate 0.0025% and novaluron 0.01% were found moderately effective. The treatments of acephate 0.075% and thiamethoxam 0.005% were found least effective insecticides and recorded higher larval population.
The higher efficacy of chlorantraniliprole against H. armigera was reported by Joshi (2011), Sreekanth et al. (2014) and Kumar and Sarada (2015). The effectiveness of flubendiamide against H. armigera was reported by Gowda et al. (2003) and Kumar and Sarada (2015). These all reports are in agreement with present findings.