EVALUATION OF DIFFERENT DOSES OF SOME PROMISING INSECTICIDES AGAINST MAJOR INSECT PESTS OF OKRA AND THEIR EFFECT ON NATURAL ENEMIES

Abstract

The study was conducted in the experimental field of Sher-e-Bangla Agricultural University, Dhaka-1207 during the period from March, 2022 to July, 2022 to find out the efficacy of different doses of some promising insecticides against major insect pests of okra and their effect on natural enemies. The treatments of the experiment were composed of three different doses of three promising insecticides with a untreated control viz. T 1 = Belt 24 WG (flubendiamide) @ 0.25 gm/L water, T = Belt 24 WG (flubendiamide) @ 0.50 gm/L water, T = Belt 24 WG (flubendiamide) @ 0.75 gm/L water, T 4 3 = Voliam flexi 300 SC (chlorantraniliprole + thiamethoxam) @ 0.25 ml/L water, T = Voliam flexi 300 SC (chlorantraniliprole + thiamethoxam) @ 0.50 ml/L water, T 5 = Voliam flexi 300 SC (chlorantraniliprole + thiamethoxam) @ 0.75 ml/L water, T 6 = Pine 6 WG (emamectin benzoate + abamectin) @ 0.25 gm/L water, T 8 7 = Pine 6 WG (emamectin benzoate + abamectin) @ 0.50 gm/L water, T = Pine 6 WG (emamectin benzoate + abamectin) @ 0.75 gm/L water and T = Untreated Control. The experiment was laid out in Randomized Complete Block Design (RCBD) with three replications. Each of the treatments was applied at 10 days interval and data was taken before each spraying. The data were recorded on shoot infestation at vegetative and fruiting stages; fruit infestation at early, mid and late fruiting stage; plant and yield related attributes as well as yield of okra. Among nine treatments, T reduced the highest percent of shoot infestation (66.58 & 75.94%) over control at vegetative and fruiting stage, respectively followed by T 9 (58.35 & 75.94%, respectively); whereas, T 1 8 showed the least performance (42.51 & 63.05% respectively). In case of fruit infestation, T produced the least number of infested fruits by number (1.08, 0.83 & 0.79) at early, mid and late fruiting stages, respectively followed by T 3 , T 4 and T 8 ; whereas, T 6 9 showed the poor performance after control treatment. Considering plant and yield related attributes, T produced maximum number of fruit (35.17) followed by T 9 (34.07) and T 5 8 (31.67); fruit length (15.71) and girth (6.40) and highest single fruit weight (26.51 gm) followed by T . At vegetative stage, jassid and whitefly population was lowest (0.25) and (0.12) observed from T 8 and T treatment respectively. The untreated plot influenced largest number of jassid and whitefly population (1.13 and 1.35) at vegetative stage. The jassid and whitefly was recorded lowest (1.18 and 0.83) from T 5 at flowering stage of okra. In case of natural enemy (ladybird beetle, black ant, spider, lacewing and syrphid fly) the untreated plot generated maximum number followed by T 9 whereas; the higher doses for each insecticide yielded lowest number of population compare to control. In case of all yield attributing characters, the untreated control showed the least performance. Similarly, the highest fruit yield (19.56 ton/ha) was also achieved by T 1 with the increase of 51.50% yield over control; whereas, T showed the least performance (13.91ton/ha) with the lowest percent of yield increase (7.75%). The yield of okra was negatively correlated with shoot infestation (r = -0.451), but positively correlated with single fruit weight (r = 0.970) whereas, length of fruit is positively correlated with single fruit weight (r = 0.961). So, recommended doses of insecticides are better for getting best economic return from okra production.