F.R. Bora, A.A.L.H. Baruah, B. Bhattacharyya and D. Sharmah
Abstract
The experiment was conducted at the ICR farm of Assam Agricultural University, Jorhat, Assam during 2010-2011 to evaluate the Bio-efficacy of some insecticides on cowpea aphid, Aphis craccivora. All the insecticidal treatments were found to be significantly superior over control. Among the insecticides, the lowest incidence and the highest population reduction of aphid population was obtained with imidacloprid at 30g a.i.ha-1 9.03, 6.07, 2.40, 6.70 numbers and 67.44, 78.13, 91.18, 76.67 per cent after one day, three days, seven days and ten days of spraying followed by fipronil 60g a.i.ha-1 with 9.13, 6.17, 3.00, 7.93 numbers and 70.17, 79.85, 90.13 and 74.07 per cent after one day, three days, seven days and ten days. There was no significant difference among 20 and 30g a.i.ha-1 of imidacloprid at one and three days after spraying. But the higher concentration of imidacloprid (30g a.i.ha-1) was significantly superior over other two concentrations at seven and ten days after spraying. The highest mean yield was obtained from imidacloprid 30g a.i.ha-1 (5.88qha-1) followed by fipronil 60g a.i.ha-1 (5.74 qha-1) which were significantly more than that obtained in standard checks malathion 450g a.i.ha-1 (5.34 qha-1). Higher yield was also recorded with imidacloprid 20g a.i.ha-1 (5.57 qha-1) which as at par with malathion 450g a.i.ha-1. The highest benefit was obtained from the treatment imidacloprid 30g a.i.ha-1 with a benefit-cost ratio of 4.35:1 followed by imidacloprid 20g a.i.ha-1 and fipronil 60g a.i.ha-1 with a benefit-cost ratio of 3.72:1 and 3.42:1 respectively. The least benefit was obtained with the treatment of thiamethoxam 100g a.i.ha-1 with a benefit-cost ratio of 0.04:1.