D3143: Response of field populations of corn earworm and fall armyworm to four insecticides and evaluation of the insecticide sprays on silks in sweet corn

Corn earworm (CEW), Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), and fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), cause damage in sweet corn (Zea mays L.). Our objectives were to: (1) evaluate the response of CEW and FAW larvae to four insecticides, and (2) determine the most appropriate time for insecticide applications. ß-cyfluthrin (0.4 ml/l), emamectin benzoate (0.2 g/l), chlorantraniliprole (0.6 ml/l), and spinetoram (1.5 ml/l) were applied on larvae collected from Isabela and Lajas. Also, the aforementioned insecticides were sprayed on 4 days-old silks, 3 h before pollinations; and 24 and 48 h after pollinations. Percentages of larval mortality were noted at 96 h after the insecticide applications. Furthermore, the number of kernels per ear and the CEW/FAW severity were quantified at harvest. The applications of emamectin benzoate caused over 75% of FAW larval mortality in both locations. Spinetoram caused FAW larval mortality of 70% in Lajas and 30 and 36% for FAW and CEW, respectively in Isabela. Unlike, applications of ß-cyfluthrin and chlorantraniliprole caused percentages of mortality below 25% in both populations. In general, insecticide applications at 3 h before pollinations reduced the number of kernels. In contrast, emamectin benzoate sprayed at 48 h after pollinations increased the number of kernels (281) and reduced the damage of CEW/FAW larvae (< 0.5%) compared to the control (229; 4.4%) in Lajas. Likewise, applications of spinetoram at the same time increased the yield (217 kernels) and reduced the CEW damage (1.8%) compared to the control (186; 7.5%) in Isabela.