Bio-efficacy of microbial insecticides against cabbage butterfly, Pieris brassicae (Lepidoptera: Pieridae) in NEH region of India

The field experiments were conducted to study the bio-efficacy of microbial insecticides against Pieris brassicae Linnaeus in cabbage crop var. “Green Hero” in NEH region of India. The pooled data of two years indicated that Metarhizium anisopliae @ 1500 g/ha proved the most effective treatment in reducing the incidence of P. brassicae with a minimum mean leaf damage of 49.93 per cent as against 67.57 per cent in untreated control followed by Beauveria bassiana 10 SC @ 1000 ml ha-1 and M. anisopliae @ 1000 g ha-1 with a record of lower mean leaf damage of 51.68 and 51.85 per cent, respectively. The treatment M. anisopliae @ 1500 g ha-1 recorded maximum cabbage yield of 17.09 t ha-1, followed by B. bassiana 10 SC @ 1000 ml ha-1 treated plots (15.19 t ha-1) and M. anisopliae @ 1000 g ha-1 (15.02 t ha-1). The minimum yield (12.84 t ha-1) was obtained from the plots treated with Dichlorvos 76 SL @ 500 ml with an increased yield of 3.09 t ha-1 over control, but, did not differ significantly from rest of the treatments. The extent of avoidable yield loss due to the incidence of P. brassicae was estimated to be 45.98 per cent in untreated control which was reduced to 9.41-28.86 per cent in treated plots. Minimum avoidable yield loss being recorded in B. bassiana 10 SC @ 1000 ml ha-1 and maximum avoidable yield loss in Dichlorvos 76 SL @ 500 ml ha-1 treatments. The net profit of the treatments varied from Rs. 28,350.00 (Dichlorvos 76 SL @ 500 ml ha-1) to Rs. 77,150.00 (M. anisopliae @ 1500 gm ha-1) with the cost-benefit ratio of 1:11.12 to 1:13.19 in the treatments. Beauveria bassiana 10 SC @ 1000 ml ha-1 gave the highest benefit-cost ratio of 1:13.19, while the lowest was in Dichlorvos 76 SL @ 500 ml ha-1 with 1:11.12.