Influence of Three Types of Borders on Field Evaluation of Insecticides for Fall Armyworm (Lepidoptera: Noctuidae) Control in Seedling Corn²

The performance of insecticides when applied against the fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), larvae in whorl stage corn was studied in relation to larval movement within and between test plots. The effectiveness of individual treatments varied in accordance with their toxicity to FAW. The degree of FAW suppression was critically influenced by the type of adjacent treatment (Exp 1). Side-by-side experimental plots with no borders gave results that made better performing insecticides look worse than they were, while poorer performers looked better. Plots having fallow (tillage only), untreated, and insecticide-treated borders (Exp 2) contained 21, 14, and 9% dead plants, respectively, from FAW feeding. Methomyl and monocrotophos gave the greatest control of FAW larvae, while trichlorfon and carbaryl were the least effective insecticides. Permethrin gave poor control with one application but improved with multiple applications to equal the effect of the methomyl standard after three applications. Azinphosmethyl gave slightly better control of FAW larvae than did carbaryl or trichlorfon but was not as effective as methomyl. Reinfestation of whorl stage corn by FAW larvae occurred with all treatments and border types. The greatest reinfestation occurred after the first of three weekly applications. Studies suggested that border types, adjacent treatments, and cumulative effect of multiple applications are factors that critically influence the performance of insecticides applied to FAW larvae in small field plots.