Impact of Helicoverpa zea (Lepidoptera: Noctuidae) feeding on yield components in double-cropped soybean with determinate and indeterminate growth habits

Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) injury to soybean (Glycine max L. Merrill) may result in yield loss. To minimize loss, economic thresholds are used to make treatment decisions. However, many of these thresholds are based on studies using determinate soybean varieties, and it remains unclear whether indeterminate varieties have a greater capacity to compensate for H. zea herbivory compared to determinate ones. For this reason, we investigated whether soybean varieties with different growth habits vary in their ability to compensate for H. zea feeding injury in double-crop systems. We hypothesized that yield and yield components would not differ by growth habit (indeterminate and determinate) or relative maturity (5.2 and 5.4/5.5), regardless of H. zea pressure. We conducted experiments across multiple locations over 2 yr, using soybean varieties with different growth habits but similar relative maturities. We found a significant relationship between larval infestation and growth habit, specifically, for individual seed weight, with indeterminate varieties showing increased seed weight as larval infestation increased. However, we did not observe this relationship for other yield components or overall yield. Our findings suggest that indeterminate soybean varieties may have greater compensatory ability in response to biotic stressors than determinate varieties, likely due to their extended vegetative growth window may allow for greater compensation. Nevertheless, we conclude that current economic thresholds remain appropriate for both determinate and indeterminate soybean varieties in double-crop systems. We recommend additional research across more varieties and environments with higher H. zea pressure to better understand soybean compensatory responses to insect injury and damage.