Spraying Cry1A.105 + Cry2Ab2 Bt sweet corn has marginal benefit for Helicoverpa zea (Lepidoptera: Noctuidae)...

Management of corn earworm, Helicoverpa zea Boddie (Lepidoptera: Noctuidae) in fresh-market sweet corn requires multiple, precisely timed applications of effective insecticides. An alternative method to manage H. zea is sweet corn hybrids that express Bacillus thuringiensis (Bt) toxins, but this approach has become limited because H. zea populations have developed resistance to multiple Bt toxins. We hypothesized that spraying a marginally performing Bt hybrid with an effective insecticide would provide a level of H. zea control that neither approach could achieve independently. To test this idea, we compared H. zea control using Cry1A.105+Cry2Ab2 Bt sweet corn treated with chlorantraniliprole following either a 7, 4, or 2-3 day silk-stage spray schedule with control following the same spray schedule and the non-Bt isoline. This study was conducted in high and low H. zea pressure environments in 2024 and 2025. Results showed that the combination of insecticidal sprays and the Bt hybrid provided minimal additional benefit relative to the sprays alone. We did find that weekly applications of chlorantraniliprole resulted in measurable reductions in H. zea damage, but the benefit of additional sprays dissipated with increasing frequency. This effect was most apparent where H. zea pressure was low and there was no statistical separation among spray interval treatments. Our results highlight the challenge of producing undamaged sweet corn, even when a Bt hybrid is treated intensively with an insecticide. Outcomes show that existing action thresholds may need revision to include additional variables that are sensitive to current input and damage costs.