EVALUATION OF SYNTHETIC INSECTICIDES FOR CONTROL OF FALL ARMYWORM (SPODOPTERA FRUGIPERDA, J.E. SMITH) IN THE GUINEA SAVANNAH AGRO ECOLOGY OF GHANA

Abstract

The Fall Armyworm (FAW), Spodoptera frugiperda (J.E Smith) is an alien invasive insect pest in tropical Africa. The recent spread of the pest to Ghana has triggered rampant spraying of all sorts of synthetic insecticides to control the pest. Studies were conducted to evaluate nine synthetic insecticides belonging to different chemical groups for their efficacy against the FAW in maize. The effects of the insecticides on larval mortality were evaluated in laboratory bioassay at 12 hr. to 96 hr. of exposure, and subsequently in the field to assess their efficacy and impact on maize yield. Completely randomized design (CRD) and randomized complete block design (RCBD) were used for the laboratory and field experiments, respectively. There were significant differences among the treatments. From the laboratory results, the highest larval mortality (100%) was recorded on Emamectin Benzoate 12g/L + Acetamiprid 64g/L (Ema star) and Emamectin Benzoate 12g/L + Imidacloprid 50g/L (Dean) treatments. This was followed by those of Emamectin Benzoate 1.9% (Wv) EC + Nonhazardous Ingredient 98.1% (Attack) and Chlorpyrifos 400g/L + Deltamethrin 24g/L EC (Pyrinex quick) which recorded 96% and 50% mortality, respectively. The least mortality (13%) was observed in Imidacloprid 250g/L + Bifenthrin 50g/L (Galil), Azadirachtin (Neemazal) and Teflebenzuron 75g/L + Alphacypermethrin 75 g/L (Normax). Results of the field trial indicated that Emamectin Benzoate 12g/L + Acetamiprid 64g/L (Ema star)significantly reduced population of FAW and number of infested whorls compared to those of the control and the other insecticide treatments. However, mortality from Emamectin Benzoate 12g/L + Acetamiprid 64g/L (Ema star) treatment was not significantly different from that of Emamectin Benzoate 12g/L + Imidacloprid 50g/L (Dean). Moreover, there were significant differences in maize yield among the insecticide treatments. Maize plants sprayed with Emamectin Benzoate 12g/L + Acetamiprid 64g/L (Ema star) and Emamectin Benzoate 12g/L + Imidacloprid 50g/L (Dean) yielded almost three times the yield of the control and the other insecticide treatments Azadirachtin (Neemazal), Teflebenzuron 75g/L + Alphacypermethrin 75 g/L (Normax) and Imidacloprid 250g/L + Bifenthrin 50g/L (Galil). Therefore, Emamectin Benzoate 12g/L + Acetamiprid 64g/L (Ema star) and Emamectin Benzoate 12g/L + Imidacloprid 50g/L (Dean) were the most recommended insecticides for the control of FAW and for maximum productivity of maize in the savanna ecology of Ghana.