Evaluation of Selected Bio-rational and Synthetic Insecticides Against Onion Thrips (Thrips tabaci L.) (Thysanoptera: Thripidae) on Onion (Allium cepa L.) in the Central Rift Valley of Ethiopia

Abstract

Onion thrips, Thrips tabaci (Thysanoptera: Thripidae) is a key insect pest of onion. Onion growers at Meki and Batu locations rely on synthetic insecticides to control onion thrips. This practice encourages the development of insecticide resistance. Therefore, the search for alternative measures has become increasingly important. The present study was designed to evaluate the efficacy of selected bio-rational insecticides and the efficacy of selected synthetic and bio-rational insecticides in rotation against onion thrips. Field experiments were conducted in two locations at Meki and Batu, Eastern Shewa of Oromiya Regional state of Ethiopia during the dry season of 2019/2020. Two experiments were laid out in a randomized complete block design (RCBD) with four replications. Experiment one evaluated the efficacy of bio-rational insecticides (nimbecidine, spinosad, spinetoram, mixture of natural plant extracts and phytoenzyme, Sophora flavescens plant extract 25% + emamectin benzoate 1% SL, Milletia ferrugienea, profenofos (as a standard check) and untreated plots). Experiment two evaluated efficacy of selected bio-rational and synthetic insecticides in rotation (nimbecidine + profenofos, nimbecidine + imidacloprid, mixture of natural plant extracts and phytoenzyme + profenofos, mixture of natural plant extracts and phytoenzyme + imidacloprid, imidacloprid, profenofos (as a standard check) and untreated plots). The study showed that all the biorational insecticides reduced thrips population when compared with the untreated plots. Spinosad, nimbecidine and mixture of natural plant extracts and phytoenzyme effectively controlled thrips on onion and were comparable to the standard check insecticide (profenofos) and gave significantly higher yield than the untreated. Nimbecidine + profenofos and mixture of natural plant extracts and phytoenzyme + profenofos in rotation treatments effectively controlled thrips on onion and were comparable with the standard insecticide (profenofos). The highest yield (29.75, 31.22 ton/ha) was obtained from nimbecidine + profenofos in rotation treatment and the lowest (13.93, 14.36 ton/ha) from the untreated. Thus, spinosad, nimbecidine and mixture of natural plant extracts and phytoenzyme as a sole application or nimbecidine + profenofos and mixture of natural plant extracts and phytoenzyme + profenofos in rotation can be used to control onion thrips on onion