Economic injury levels of fall armyworm (Spodoptera frugiperda Smith) at early-whorl vegetative growth stage of quality protein maize variety

Abstract

Screen-house experiments were conducted in 2020 and 2021 wet seasons to determine the Economic Injury Levels (EIL) of fall armyworm (Spodoptera frugiperda Smith) at the early-whorl vegetative growth stage (V4) of SAMMAZ 36 quality protein maize (QPM) variety at Samaru, Zaria, Nigeria. The variety grown in different plastic pots was placed in separate wooden cages at the screen-house and artificially infested with different larval densities (0, 2, 4 and 6) of fall armyworm (FAW) per plant at two weeks after emergence. The experiments were laid out in a completely randomized design (CRD) and repeated three times. Relationship between FAW larval densities and cob damage rating, grain yield (kg/ha) and percent yield losses were determined by coefficient of determination (R²) and regression equation. The results showed that plants with zero infestation had the highest grain yield, and the grain yields of infested plants decreases with increase in number of FAW larvae. Infestation with 6 larvae per plant in 2020 and 2021 experiments resulted in yield losses of 28.2 and 26.1%, respectively. Regression of grain yield and FAW larval densities was negative and linear, for the early-whorl growth stage of SAMMAZ 36 in both years. The EIL values determined from this study were 4.44 and 3.32 FAW larvae per plant in 2020 and 2021 seasons, respectively. Based on these findings, when FAW densities of at least three larvae per plant are detected at the early-whorl (21- 28 days after emergence) vegetative growth stage of maize, control measures should be initiated to prevent FAW population build up and economic damage.