Comparative Field Efficacy of Microbial and Conventional Insecticides against Bollworms of Cotton

Field efficacy of microbial and conventional insecticides against bollworms on cotton was evaluated in 2004-05. All the treatments reduced the bollworm infestation on squares, green bolls and open bolls and consequently increased the seed cotton yield significantly over untreated control during both the years. Spinosad 45 SC 75 g a.i. ha^-1 proved most effective in reducing the bollworm infestation and increasing the seed cotton yield. It recorded the lowest infestation of bollworms on squares (10.24 and 9.56%), green bolls (9.56 and 8.31%) and open bolls (6.22 and 4.86%) and the highest seed cotton yield (1687 and 1695 kg ha^-1) followed by indoxacarb 14.5 SC 75 g a.i. ha^-1, endosulfan 35EC 560 g a.i. ha^-1 and Bacillus thuringiensis var. kurstaki 1.5 kg ha^-1. Among the microbials, B. thuringiensis var. kurstaki 1.5 kg ha-1 was significantly better than Ha nuclear polyhedrosis virus 250 LE ha^-1 only in respect of bollworm infestation on open boll basis during both the years and was found comparable to spinosad 45 SC 75 g a.i. ha^-1 in respect of bollworm infestation on green and open bolls during the first year and on squares during the second year and seed cotton yield during both the years.