On-farm large plot comparison of Bt and non-Bt corn hybrids for <i>Helicoverpa zea</i> (Lepidoptera: Noctuidae) feeding, yield, and economic return

Abstract

Helicoverpa zea (Bodie) is a widespread damaging pest in the US that has evolved varying levels of resistance to Cry toxins in corn and cotton. To delay resistance evolution to this pest and others targeted by Bt corn, growers in the southern United States are required to plant at least 20% of their corn area with non-Bt corn. However, growers are reluctant to do this. Multiple small-plot research studies show timely planted non-Bt and Bt corn hybrids yield equally; however, growers often think non-Bt hybrids yield less than Bt hybrids. In response, we compared non-Bt and Bt hybrids using grower-owned planting and harvesting equipment. Growers planted 5 corn hybrids as strip plots (Bt-P1197YHR, DKC65-99, non-Bt-P1197LR, DKC67-70, and DKC65-93) in 2022 at 27 locations and 4 hybrids (excluding DKC65-93) in 2023 at 28 locations throughout North Carolina. When corn reached dent (R5), we measured the area of H. zea injury from each hybrid at each location. We calculated yield and economic net returns at harvest. We separated analyses for Bt trait pyramid and hybrid for both feeding and yield. H. zea feeding was at moderate levels, following predictable patterns. There were no significant differences between Bt and non-Bt hybrids within the 2 companies we compared (Pioneer [P] and Bayer [DKC]) across both years. In general, farm profitability is not statistically different when planting a 20% non-Bt refuge compared to planting 100% Bt corn. Factors other than typical H. zea feeding are more impactful on yield in North Carolina.