Effect of cultivars and insecticidal treatments on fall armyworm, Spodoptera frugiperda (J.E. smith), infestation and damage on maize

Abstract

Fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), is an economically important insect pest of maize in most African countries, including Ghana. Hence, this study tested the efficacy of selected biorational and synthetic insecticides for the control of FAW in two maize cultivars in Ghana. The cultivars, Ewul-boyu and Wang-dataa, and the insecticides, neem seed oil (NSO) (azadirachtin), Agoo (Bacillus thuringiensis, Bt + Monosultap), KD 215 EC (Chlorpyrifos + Lambda-cyhalothrin) and K-Optimal (Lambda-cyhalothrin + Acetamiprid), were arranged in split-plots design. Data were collected on FAW larval infestations, damage and yield. Cultivars had no significant effect on the variables measured. Mean larval infestation before treatments application were not significantly different (P > 0.05) among the insecticides tested. After treatments application, infestation was highest in the untreated control and lowest in maize treated with K-Optimal. Damage levels (following Davis scale) in the untreated control (5.3) was significantly higher than in the insecticide treatments (3.0–3.6). Yields were at least 1.7-fold higher in all insecticide treatments than in the untreated control in both years. The benefit-cost (BC) ratios showed that farmers who do not protect their maize (untreated control) can break even. However, using either biorational or synthetic insecticides resulted in between 1.5 and 2.0-fold returns on investment with Agoo having the highest. In conclusion, the maize cultivars tested are not resistant to FAW. Therefore, farmers should use environmentally safe insecticides (e.g., NSO or Bt) to mitigate FAW damage since their efficacy and economic returns are not different from those of synthetic origins.