A Comparative Analysis of Chemical and Bio-Rational Management of Insect Pests of Cabbage

To test certain bio-rational insecticides against the diamondback moth, Plutella xylostella Linnaeus and cabbage butterfly, Pieris brassicae Linnaeus and their toxic effect on the population of ladybird beetle, Coccinella septempunctata Linnaeus in the Manipur valley cabbage crop-ecosystem, a field trial was carried out during Rabi, 2022–23 at the Vegetable Research Farm of the College of Agriculture, Central Agricultural University, Imphal. The mean extent of damage caused by P. xylostella and P. brassicae was high ranging from 62.67 to 88.34% and 83.33 to 92.11%, respectively, over the investigation period. The effectiveness of bio-rational pesticides against P. xylostella and P. brassicae was determined by the results of the insecticidal treatments, which showed a considerable reduction in the incidence of these pests. Malathion 50 EC applied @ 500 ml/ha witnessed the most effective insecticide against the diamondback moth, P. xylostella with a record of minimum mean leaf damage of 19.36% as against 50.08% in untreated control, closely followed by Greenracer (Beauveria bassiana) @ 1000 ml/ha (20.37%), and Neemajal (Azadirachtin 1500 ppm) @ 1000 ml/ha (22.37%) but, differed significantly from each other except with green racer. Among the phytoproducts, the plots treated with Neemajal (Azadirachtin 1500 ppm) @1000 ml/ha recorded the lowest DBM incidence (22.37% leaf damage) which was at par with Pestoneem (Azadirachtin 1500 ppm) @ 1000 ml/ha (24.57% leaf damage). Against P. brassicae also Malathion @ 500 ml/ha substantially recorded the lowest mean leaf damage of 22.67 vs 82.56% in the untreated check, followed by Greenracer with a record of 26.12% leaf damage, however, there were significant differences. Neemajal (Azadirachtin 1500 ppm) @1000 ml/ha was demonstrated to be the most effective treatment in reducing the pest incidence with the lowest mean leaf damage of 28.67% among the botanical insecticides field tested against cabbage butterfly butterflies. The highest mean leaf damage incidence (37.11% LD) was noticed in the plots treated with Pacer (Metarrhizum anisoplae) @ 1000 ml/ha. The efficacy of Pestoneem (Azadirachtin 1500 ppm) @ 1000 ml/ha, Multineem (Azadirachtin 300ppm) @1500ml/ha and Neemta (Azadirachtin 300ppm) @1500ml/ha was at par from each other recording mean leaf damage of 34.78, 35.56 and 36.89% respectivelyThe plots treated with Malathion @ 500 ml/ha yielded the highest mean cabbage yield (23.67 t/ha), with a maximum yield increase over control of 9.34 t/ha and 65.17%. These yield increases were non-significantly different from those of the Green Racer plots (22.67 t/ha), Neemajal (20.09 t/ha), Pestoneem (20.04 t/ha), Mutlineem (19.44 t/ha), and Neemta (19.32 t/ha), which yield increases of 8.34 t/ha, 5.76 t/ha, 5.71 t/ha, 5.11 t/ha, and 5.00 t/ha, respectively, whereas Pacer treated plots accrued significantly lowest cabbage yield of (18.43%) with a record of lowest yield increase over control of 4.1 t/ha and 28.61%. The avoidable yield loss was computed to be 40.82 percent in the untreated control plots. Application of insecticides resulted in a reduction of the mean avoidable yield loss, which ranges between 4.22 and 20.74 percent in different insecticidal treatments, the lowest being in Greenracer (Beauveria bassiana) and the highest in Pacer (Metarrhizum anisoplae). The net profit of the insecticidal treatments varied from Rs. 19595.60 (Pacer) to Rs. 35364.7 (Malathion 50 EC) with the cost: benefit ratios ranging between 1:11 to 1:46, the minimum and maximum being with Neemajal and Green Racer, respectively.

The results on the toxic effect of insecticides on the population of C. septempunctata indicated that the minimum mean population (0.52 beetles/plant) was recorded from Malathion 50 EC @ 500 ml/ha treated plots which were at par with Neemta (Azadirachtin 300ppm) (0.84 beetles/plant), Multineem (Azadirachtin 300ppm) (0.90 beetles/plant) and Pestoneem (Azadirachtin 1500ppm) (0.93 beetles/plant), respectively. However, the maximum population of beetles (1.39 beetles /plant) was marked in the plots of Greenracer which did not differ significantly from the rest of the insecticidal treatments.