Corn earworm populations in Pennsylvania field corn and the value of Bt for controlling ear damage

Field corn hybrids expressing Bt toxins are popular choices for controlling European corn borer, Ostrinia nubilalis, and western corn rootworm, Diabrotica virgifera; however, these hybrids also have activity against several noctuid pests, including the corn earworm, Helicoverpa zea.  Across the United States, corn earworm is an important pest of many agricultural crop species.  To understand corn earworm populations in Pennsylvania field corn and the value of Bt hybrids for control, we assessed ear damage at sixteen sites across four maturity zones in 2010, and ten sites in 2011.  We also used mid-season captures of corn earworm in pheromone traps to predict ear damage at the end of the season.  Corn earworm damage in non-Bt hybrids exceeded one bushel/ha at only three locations over two years, and caterpillars generally damaged less than 15% of ears surveyed.  Bt hybrids decreased corn earworm damage by 40-70% relative to non-Bt hybrids, but we did not detect differences in control among Bt events.  Analyses of moth captures and in-field damage revealed that cumulative male captures through July were strongly correlated with damage at the end of the season.  Moth captures may give growers an estimate of damage caused by corn earworm, and also provide insight into whether growers are gaining economic benefits by using Bt hybrids for corn earworm control.  Our research suggests that corn earworm populations in field corn remain low and investing in Bt hybrids targeting corn earworm may not provide an economic return unless damage from other caterpillar species is significant.