[Objectives]  To compare the effectiveness of field surveys, pheromone traps, and high-altitude reporting lamps for  monitoring the population dynamics of the armyworm Spodoptera frugiperda in spring cornfields. [Methods]  A field study to determine the per-plant larval density was conducted in 2022 in Danzhou, Hainan Province. Concurrently, adult armyworms were lured into traps using pheromone lures and high-altitude reporting lamps, and the results obtained from these three monitoring methods were then compared. [Results]  The armyworm population experienced two population peaks during the corn growth cycle, the first during the jointing and trumpet mouth stages, when density reached up to 140 larvae per 100 plants, and the second during the milk stage when density was 119 larvae per 100 plants. Pheromone trapping data were closely aligned with the results of the field survey, although the population peaks occurred 4-6 days later. High-altitude reporting lamps detected three minor peaks during the seedling, whorl, and mature stages, but these were less distinct. Regression analysis revealed a significant positive correlation (R² = 0.49, P < 0.001) between the number of adult armyworms caught in pheromone traps and the field survey counts. [Conclusion]  Field surveys offer the most direct insights into armyworm population dynamics. Pheromone trap results were closely aligned with field survey data, and are therefore a good alternative for monitoring armyworm population dynamics. High-altitude reporting lamps are effective for tracking migrating populations. Utilizing a combination of these methods allows for comprehensive monitoring of both armyworm ground-level abundance and aerial migration patterns.