Botanical-chemical pesticide combinations for managing cowpea aphid Aphis craccivora Koch

Abstract

The present investigation on “Botanical-chemical pesticide combinations for managing cowpea aphid Aphis craccivora Koch” was conducted at the Department of Agricultural Entomology, College of Agriculture, Vellayani during 2020 to 2022 with an objective to study the effect of botanical-chemical pesticide combinations for managing cowpea aphid Aphis craccivora in cowpea. Fourteen treatments namely Neem oil emulsion 2%+ Thiamethoxam 0.02%, Neem oil emulsion 2%+ Thiamethoxam 0.01%, Neem oil emulsion2%+ Thiamethoxam 0.005%, Pongamia oil emulsion 2%+Thiamethoxam 0.02%, Pongamia oil emulsion 2%+ Thiamethoxam 0.01%, Pongamia oil emulsion 2%+Thiamethoxam 0.005%, Andrographis formulation 5 % (Bhavyasree, 2019) +Thiamethoxam 0.02%, Andrographis formulation 5 % (Bhavyasree, 2019) +Thiamethoxam 0.01%, Andrographis formulation 5 % (Bhavyasree, 2019) +Thiamethoxam 0.005%, Neem oil emulsion 2%, Pongamia Oil emulsion 2%, Andrographis formulation 5% , Thiamethoxam 0.02% and Untreated control were evaluated against A. craccivora with three replications maintained under laboratory conditions. The mortality of the test insect was recorded at 12, 24 and 48 h after treatment and the data were statistically analysed. After 24 h of treatment, the highest mortality was shown by Thiamethoxam 0.02% (88.89 per cent), followed by Pongamia oil emulsion 2% +Thiamethoxam 0.02% (76.67 per cent) and Neem oil emulsion 2% + Thiamethoxam 0.02% (70 per cent). After 48h of treatment, same trend was observed and Thiamethoxam 0.02% recorded highest mortality (99 per cent), followed by Pongamia oil emulsion 2% +Thiamethoxam 0.02% (90.44 per cent) and Neem oil emulsion 2% + Thiamethoxam 0.02% (81.89 per cent). Based on the in-vitro study, three treatments were chosen for field evaluation namely Pongamia oil emulsion 2% + Thiamethoxam 0.02%, Neem oil emulsion 2% + Thiamethoxam 0.02% and Thiamethoxam 0.02%. Three prophylactic sprays were given at 15, 35 and 55 days after sowing for field evaluation and data were recorded at 1,3,5 and 7 days after treatment. The field data were evaluated using the 2 Way Analysis of Covariance (ANCOVA). The treatments Pongamia oil emulsion 2% + Thiamethoxam 0.02% and Neem oil emulsion 89 2% + Thiamethoxam 0.02% showed significantly lower population of aphid A. craccivora when compared with the chemical check and control. Seven days after first spray, the mean population of aphids per plant were significantly lower in the plots treated with Pongamia oil emulsion 2% + Thiamethoxam 0.02% (1.36 per plant) followed by the Neem oil emulsion 2%+ Thiamethoxam 0.02% (1.94 per plant) and both the treatments exhibited a steady decline in the aphid population when compared with control. The similar trend was followed in the second spray (35 days after sowing) and third spray (55 days after sowing). Testing the effectiveness of these treatments against pod bugs, Riptortus pedestris, the results were similar to that of A. craccivora population. The effects on the natural enemies viz, coccinellid (adult and larvae), brown lacewings, spiders and syrphids were recorded. The analysed data showed that the plots treated with Pongamia oil emulsion 2% + Thiamethoxam 0.02% and Neem oil emulsion 2% + Thiamethoxam 0.02% harboured significantly higher population of natural enemies when compared with the standard chemical check. Symptoms like yellowing, scorching, necrosis, epinasty and hyponasty were observed for phytotoxicity studies and the above treatments did not exhibit any form of phytotoxicity. All the treatments exhibited significant variation in fresh pod weight. The highest yield was recorded in the plots treated with Pongamia oil emulsion 2%+Thiamethoxam 0.02% (854 g/plot), which was followed by Neem oil emulsion 2%+Thiamethoxam 0.02% (776 g/plot). Traces of chemical residue (0.011ppm) were detected in chemical check (Thiamethoxam 0.02%), but it is below the limit of quantification (< LOQ), whereas the plots treated with Pongamia oil emulsion 2% + Thiamethoxam 0.02% and Neem oil emulsion 2% + Thiamethoxam 0.02%, did not detect any residue. From the study, it can be concluded that the combination of Pongamia oil emulsion 2% + Thiamethoxam 0.02% and Neem oil emulsion 2% + Thiamethoxam 0.02%, were effective in controlling aphid and pod bug population and they also supported the population of natural enemies when compared to chemical check (Thiamethoxam 0.02%). The chemical-botanical combinations supported good yield of cowpea and also reported thiamethoxam residue below limit of quantification.