Infestation of Fall Armyworm (Spodoptera frugiperda): Insights From Season, Crop Phenology and Growing Degree Days

Abstract

This study revealed that among climatic factors, rainfall, temperature, and relative humidity significantly affected the seasonal population of fall armyworm (FAW). The drier weather favoured its movement and spread whereas rainy weather with higher humidity reduced adults' foraging and larval activity. The seasonal fluctuations of population showed peaks during specific time periods corresponding to specific crop stage of maize. The damage scores, alone, were insufficient indicators for assessing maize yield losses by FAW, as plant damage and FAW infestation varied across the growth stages of maize. Moreover, variable cropping seasons and weather conditions (rainy or dry) across ecological zones significantly influenced the developmental duration of both maize and FAW. Accumulated growing degree days (GDDs) in combination with crop phenological stages proved to be effective tools for predicting FAW occurrence, infestation severity, and optimal timing for management interventions. Although temperature showed a strong association with GDDs accumulation of both maize crop and FAW, deviations from optimal thermal conditions resulted in non-linear responses in crop development and FAW activity. Hence, suggesting a regular monitoring of crop regarding FAW incidence in relation to GDDs and crop phenology. Overall, these findings highlighted that the vegetative phase of maize, especially at 4–6 leaf stages, were found very critical for FAW damage, underscoring the utmost important time window to manage FAW effectively. Moreover, integrated consideration of climatic factors, crop phenology, and thermal requirements (GDDs) is essential for effective and predictive management of fall armyworm in maize cropping systems.