Efficacy of Different Pesticides on White Mango Scale (Aulacaspis tubercularis Newstead) (Hemiptera: Diaspidadae) at Guraferda, Southwestern Ethiopia

Abstract

White mango scale (WMS), Aulacaspis tubercularis Newstead, was reported for the first time in Ethiopia in 2010. Since that time, WMS is widely distributed in Ethiopia, causing significant damage to mango, (Mangifera spp.). It is a serious pest of mango which became recently a wearisome pest in mango orchards in Ethiopia. The pest inserts its stylets in and sucks sap from leaf, fruit, twigs and other young mango parts causing damages to the plant. As no single insecticide has been registered for use against the pest in Ethiopia, the objective of the study was to identify insecticides with the highest efficacy on WMS. A field study was carried out at seka agroprocessing private Ltd mango farm in southwestern Ethiopia, Bench-Sheko zone of SNNPR, during 2019 at flowering (peak incidence) season. Treatments were evaluated either in the form of alone or in rotational spray for three back-to-back applications at fortnight intervals. Fourteen insecticidal treatments, along with untreated control, were tested as part of IPM practice on ‘Tommy Atkins’ variety which is highly susceptible to WMS. Ten treatments (i.e., Dimethoate 40%, Chlorpyrifos-ethyl 48%, Endosulfan 35%, Azadirachtin 0.03%, Diazinon 60%, Imidacloprid 12.5% & λ-cyhalothrin 5%, λ-cyhalothrin 5%, Deltamethrin 2.5%, Fipronil 5%, and Paraffin oil) were applied alone, while four treatments (i.e., Dimethoate 40% rotated with Imidacloprid 12.5% & λ-cyhalothrin 5%, Chlorpyrifos-ethyl 48% rotated with Azadirachtin 0.03%, Diazinon 60% rotated with Azadirachtin 0.03%, and Deltamethrin 2.5% rotated with Paraffin oil) were applied in rotation, and untreated control were included in this trial. The experiment was laid out in RCBD and replicated thrice with a row of mango trees as a barrier in between. The manufacturer’s rate was employed for all insecticides; except paraffin oil 2.5% was used. Mean number of WMS per leaf before and after each spray was counted. Mean number of insects from post spray were used to assess the efficacy of the insecticides. From this study, Dimethoate 40%, Chlorpyrifos-ethyl 48%, Diazinon 60%, Imidacloprid 12.5% & λ- cyhalothrin 5%, Paraffin oil, Dimethoate 40% rotated with Imidacloprid 12.5% & λ-cyhalothrin 5%, Chlorpyrifos-ethyl 48% rotated with Azadirachtin 0.03%, and Diazinon 60% rotated with Azadirachtin 0.03% showed superior efficacy (100%) against WMS after the third sprays at fortnight interval that was statistically significant compared to the control and rest of the pesticides. However, the rotational spray is preferred to the alone spray, as the former could reduce the likelihood of inducing pesticide resistance substantially. No phytotoxic effects were displayed by those insecticides. Improved mango varieties that are less susceptible to WMS infestation should be looked for, studied systematically and introduced to Ethiopia by taking all necessary safety measures. Studies on natural enemies should be sought to exploit bio-control agents. Development & deployment of an effective IPM strategy is required; and those insecticides identified in current study could serve as part and parcel of IPM in the mg’t of WMS