Quantification of Yield Losses in Maize Attributed to Fall Armyworm (Spodoptera frugiperda) Infestation

A field experiment was conducted to assess avoidable yield losses caused by the fall armyworm, Spodoptera frugiperda, on maize during the kharif seasons of 2023–24 and 2024–25. Pooled data across both years indicated a significant decline in grain yield with increasing larval density per plant. The highest yield (4794.05 kg/ha) was obtained in infestation-free plots, while the lowest (4005.16 kg/ha) was recorded at a density of five larvae per plant. Grain yield and larval population showed a strong negative correlation (r = –0.99). Avoidable yield losses ranged from 3.71% to 16.46%, increasing proportionally with larval density. The results showed that avoidable yield loss increased consistently with FAW larval density (r = 0.99). Maximum losses occurred at five larvae per plant, reaching 14.26%, 18.75%, and 16.46% in 2023–24, 2024–25, and the pooled dataset, respectively. In contrast, minimum losses were recorded at 0.5 larvae per plant, with 3.74%, 3.67%, and 3.71% across the respective datasets. The relationship between larval density and percent avoidable yield loss was strong and positive, with a high coefficient of determination (R² = 0.97). The findings are useful in defining economic injury levels and economic thresholds for FAW in maize, thereby supporting the development of integrated pest management strategies.