Effect of Defoliation on Growth, Yield and Forage Quality in Maize, as a Simulation of the Impact of Fall Armyworm (Spodoptera frugiperda)

This study assesses the impact of defoliation applied to three developmental stages across three cropping seasons from 2021 to 2023 on growth, yield and forage quality in maize. The experimental design included three treatments: defoliation of three expanded leaves at the 3rd–4th leaf stage (DF1), the 5th–6th expanded leaves by leaf punch (DF2) and expanding leaves with the DF2 treatment (DF3) at the 6th–7th leaf stages, compared with no defoliation (control). Over three years, the most significant decrease in dry matter (DM) yield occurred in DF1 during spring sowing, while in summer sowing, the largest reduction was in DF3, both of which were correlated with changes in the number of grains per ear. The DM yields at harvest were positively correlated with plant leaf areas at the silking stage. The digestibility of forage in in vitro DM decreased concomitantly with an increase in acid detergent fiber content, indicating a decrease in forage quality. Given the frequent severe damage observed in summer sown maize and the detrimental effects of early growth stage leaf feeding on quality and quantity of spring sown maize, the application of registered insecticides is advised to reduce pest damage to maize crops.