Impact of Insecticide on Fall Armyworm Infestation at Different Maize Growth Stages: Insights from a Field Study in a Subtropical Region

The fall armyworm (FAW), Spodoptera frugiperda, is a significant global threat to maize production and causes adverse effects at different growth stages. We conducted this field experiment in a subtropical region to evaluate the efficacy of insecticides against FAW during various growth stages of maize in the 2022 and 2023 seasons. The results highlighted the significant influence of maize growth stages on infected plant numbers; the maturity stage exhibited the lowest infestation rates, while the late whorl stage showed the highest susceptibility, with rates of 74% and 66.7%, respectively. During the early whorl stage (VE-V6), spinosad proved the most effective insecticide, reducing the incidence to 13.5% and 18.5%, respectively. On the other hand, emamectin benzoate showed the greatest efficacy in decreasing FAW infection in the late whorl stage (V7–VT), with the lowest percentage of infected plants (57.4% and 50.4%). In the tasseling and silking stages (R1-R4), methomyl was the most effective compared to the control, significantly reducing infestation rates to 6.0% and 5.3%. Furthermore, a marked reduction in infestation rates was observed during the maturity stage (R5-R6) across all treatments, including the control. Ultimately, indoxacarb was associated with the lowest maize yield (674.5 and 650.5 kg ha-1, respectively), whereas methomyl was the most productive insecticide (2683.6 and 2742.3 kg ha-1, respectively). These findings are critical for understanding the relationship between insecticide efficacy and maize growth stages associated with the development of effective FAW management strategies.