The 3-year study compared emergence of corn earworm, Helicoverpa zea (Boddie), between seed-blend and structured-refuge systems in the field. Blocks of 95:5% (Bt:non-Bt) seed blend of Bt (P1401VYHR) and non-Bt (P1498R) maize, Zea mays L., were planted in 2014 and 2015. In 2019, blocks of 90:10% seed blend of Bt (DKC66-29) and non-Bt (DKC66-94) maize were planted. Emergence of H. zea from structured and seed-blend refuge ears was monitored using aluminum screen cages. In addition, data were gathered on the presence of Bt toxins in tip kernels of non-Bt ears from seed blend refuge plots. Significantly fewer H. zea were found in seed blend refuge ears compared to structured refuge ears in 2 of 3 years of the study. Also, the amount of damage by H. zea was significantly less in non-Bt ears from the seed blend than structured refuge ears. The percentage of kernels from non-Bt ears of seed blend refuge with expression of at least one Bt toxin ranged from 52 to 76% during 3 years of the study. Results agreed with past studies that much pollen flows from Bt plants to refuge plants in a seed blend refuge system, resulting in a mosaic of kernels expressing single or multiple Bt toxins. Such a mosaic of non-Bt and kernels with single and/or multiple toxin in a seed blend refuge system can ultimately result in less survival and emergence of H. zea.
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Vol. 45 • No. 4