Crop Protection

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    Evaluation of Selected Bio-rational and Synthetic Ins ecticides against Cabbage Aphid (Brevicoryne brassicae) (Homoptera: Aphididae) on Cabbage in the Central Rift Valley of Ethiopia
    (Hawassa University College of Agriculture, 2021) ETENESH ADNEW ALOTO
    Cabbage (Brassica oleracea L. var. capita) is one of the most popular food crops and grows well in many parts of Ethiopia. One of the constraints for the production and use of head cabbage is cabbage aphid (Brevicoryne brassicae (L.)) which damages cabbage from seedling to final growth (head formation) stage. This study aimed to evaluate the efficacy of selected bio rationales and to investigate the use of effective bio -rationales in rotation with synthetic insecticides against cabbage aphids under field conditions. Field experiments were conducted in two locations at Batu, Eastern Shewa of Oromia Regional state, and Hawassa, Sidama Regional state during the dry season of 2019/2020. Two separate expe riments were laid out in a randomized complete block design (RCBD) with four replications. The first experiment was an efficacy test of bio-rational insecticides (mixture of natural plant extracts and phytoenzyme, Spinosad, Millettia ferruginea, Nimbecidine, Sophora flavescens plant extract 25% + emamectin benzoate 1% SL, dimethoate 40% EC (as a standard check), and untreated plots). The second experiment was an efficacy test of selected bio-rational and synthetic insecticides in rotation (Nimbecidine + dim ethoate 40% EC, Sophora flavescens plant extract 25% + emamectin benzoate 1% SL+ dimethoate 40% EC, mixture of natural plant extracts and phytoenzyme + dimethoate 40% EC, Spinosad+ dimethoate 40% EC, Milletia ferruginea+ dimethoate 40% EC, dimethoate 40% EC (as a standard check) and untreated plots). The results showed that all biorational insecticides reduced aphid population when compared with the untreated plots. Spinosad, Nimbecidine, and a mixture of natural plant extracts and phytoenzyme effectively controlled aphids on cabbage and were comparable to the standard check (dimethoate 40% EC) and gave higher yield. The maximum total yield of head cabbage was obtained from dimethoate 40% EC treated plots, 57.6 tons/ha and 58.4 tons/ha, followed by Spinosad 55.4 and 56.4 tons/ ha at Hawassa and Batu, respectively; Nimbecidine 51.4 tons/ ha at Hawassa which were not significantly (P<0.05) different from dimethoate 40% EC treatment. In rotation applications of Spinosad, Nimbecidine, and a mixture of natural plant extracts and phytoenzyme with dimethoate 40% EC effectively controlled aphids on cabbage and were comparable with the sole application of standard insecticide (dimethoate 40% EC). The highest total yield of head cabbage was obtained from dimethoate 40% EC treated plots, 60.6 tons/ ha at Hawassa and 61.2 tons/ ha at Batu, and was not significantly different from Spinosad + dimethoate 40% EC treatment in both locations and Nimbecidine+ dimethoate 40% EC at Hawassa. The lowest yield (12.8, 12.4 ton/ha) was obtained from the untreated plots. Thus, Spinosad, Nimbecidine, and mixture of natural plant extracts and phytoenzyme as a sole application or Spinosad, Nimbecidine, and mixture of natural plant extracts, and phytoenzyme in rotation with dimethoate 40% EC can be used to control cabbage aphids on cabbage.
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    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
    (Hawassa University College of Agriculture, 2021) TAMENE GETAHUN BARISO
    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