Thrips, Thrips tabaci (Thysanoptera: Thripidae) on the cotton plant is an extremely invasive and destructive pest that reduces yield. Field studies were conducted at Werer Agricultural Research Center, Middle Awash, Afar, Ethiopia, for two consecutive years (2017 and 2018) to determine the effectiveness of different synthetic chemical insecticides for the control of cotton thrips (T. tabaci) on the Deltapine-90 cotton variety. A total of eleven treatments with untreated control were laid out in a Randomized Complete Block Design (RCBD) replicated thrice per treatment. The field was sprayed two times with an economic threshold level attained in two weeks intervals after the first round of data. Thrips population count data on thrips populations were collected before and after three, five, seven and ten days of insecticide application. The yield and yield component, and economic returns data were also collected. The percent efficacy was calculated using a modified Abbott's formula. The efficacy of the insecticide Rectro 20% Sc, Imidacloprid 20% SC, Closer 240% SC and Dimethoate 40% EC resulted in fewer numbers of thrips and higher yields than Diazinon 60% EC, Chlorpyrifos 48% EC, Chloropyrafose 36 SC, Deltamethrin 06% and Curadore 45%. The economic analysis of the insecticides chemical showed good cost-benefit for Rectro 20% SC (2.55), Closer 240% SC (1.93) and Dimethoate 40% EC (1.49) with good advantage. Additionally, the protection of cotton thrips using the insecticide chemicals namely Imdacloropride 20% SC, Rectro 20% Sc and Curador 45% EC would return 1.33, 1.24 and 1.24 birr return. The result confirmed that the application of more effective insecticides when the thrips population was high resulted in better control and higher economic returns. Therefore, the use of sequential applications in the insecticides, Closer 240% SC, Dimethoate 40% EC, Rectro 20%SC and Imidacloprid is recommended to manage the cotton thrips in the middle awash areas of Ethiopia.
Key words: Insect pest, resistance, management, insecticides, sequential, economic returns.
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