In 2019, fall armyworm (FAW; Spodoptera frugiperda) initially invaded the Kyushu region of Japan. As FAW is one of the most important pests to maize, this invasion posed a serious threat to forage maize production. However, the impact of FAW on forage maize has not yet been determined. Herein, summer-sown forage maize was cultivated with and without insecticide to evaluate how were the insect damage and yield loss caused by FAW in 2020. In maize cultivated without insecticide, damage to the leaves was noted between the 4-leaf stage and the tasseling stage, and on the ear in the later stages. Consequently, ear dry matter yield, total dry matter yield, and total digestible nutrition yield in the maize untreated with insecticide were 21%, 17%, and 20% lower, respectively, than those of the maize cultivated with insecticide; and thus the economic loss was estimated at approximately 210,000 yen per ha. Summer-sown forage maize is mainly cultivated in the southwestern regions of Japan. While further investigations are needed to clarify the extent of damage caused by FAW, if damage similar to our observation study occurs commonly in maize fields, an optimal pest management to FAW is required to prevent yield and economic losses.
