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The effect of period and level of infestation by the fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), on irrigated maize, Zea mays L., yield was determined. Two applications of the insecticide chlorpyriphos (336 g[ai]/ha) applied directly to the whorl produced yields equivalent to treatments with three applications. FAW infestation of 100% caused 45% yield reduction. A linear regression model (yield[g/plant] = 87.84 - 0.384 (% plants infested by FAW)) explained 46% of the yield variation. The economic injury level (EIL) was calculated as 2% of the plants infested. This low EIL is due to currently high subsidies provided pesticides in Nicaragua. The impact of pesticide subsidies on EIL's is discussed. /// Se determinó el efecto del período y nivel de infestación del gusano cogollero, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuide), sobre el rendimiento del maíz, Zea …