Interactive effects between yields of Bt and non-Bt corn and planting dates in the southeastern United States.

Transgenic corn (Zea mays L.) expressing insecticidal toxins from Bacillus thuringiensis (Bt) helps to control or suppress injury from a range of target insect pests. This study summarizes the yield benefits of Bt corn from field trials in Georgia, North Carolina, and South Carolina evaluating Bt and non-Bt corn hybrids from 2009 to 2023. For Cry1A.105 + Cry2Ab2 and Cry1Ab + Cry1F Bt corn, the percentage increase in yield between Bt and non-Bt corn hybrids did not vary significantly among years or states. Across years, the percentage increase in yield for both Bt traits relative to non-Bt corn hybrids increased with planting date, indicating that the yield benefit of planting Bt corn was greater later in the growing season. On average, Bt hybrids in both families had a significantly higher yield compared to their non-Bt pairs, with yields declining in later planting dates. Yields declined with increasing kernel injury from Helicoverpa zea (Boddie) and leaf injury from Spodoptera frugiperda (J. E. Smith) in both Bt and non-Bt hybrids. While insect pressure increased in later planted corn trials, identifying causal relationships between increases in insect damage and associated yield losses in corn is challenging given the numerous factors that influence corn yield during the season. In addition to illustrating the highly variable yield benefits of planting Bt corn, our study suggests that yield increases in Bt corn may occur more frequently than previously documented in the southeastern United States.