Grain Yield is not Impacted by Early Defoliation of Maize: Implications for Fall Armyworm Action Thresholds

The fall armyworm, Spodoptera frugiperda (J.E. Smith), now is arguably the most important global insect pest of maize, Zea mays L., in the world. Maize growers in the Americas have battled the pest for centuries, and control recommendations have been adapted for Africa and Asia, based on contrasting results of the impact on yield when the pest infests young maize plants. Important control decision-making tools such as action thresholds, or economic thresholds, are not completely developed to control fall armyworms, and insecticide applications are still recommended at low levels of infestation on young plants. To further assess the damage-yield relationship for fall armyworm, we manually removed 0, 33, and 66% of foliage when maize had 1-2 (V1-V2), and 3-4 (V3-V4) fully developed leaves. The amount of defoliation did not reduce maize yield potential when compared with nondefoliated plants, regardless of the defoliation timing: V1-V2 or V3-V4. Fertilizing defoliated plants significantly yielded more grain than non-fertilized plants, and these obvious results showed that smallholder maize growers that can afford investing in either fertilizer or insecticide will benefit more from the former. Our results add to the number of reports that indicate young maize plants can compensate for large amounts of defoliation without reducing yields.