Response of Bt and Non-Bt near-Isoline Corn Hybrids to Plant Density.

Plant density of corn (Zea mays L.) is an important consideration for maximizing grain yield and profitability. When corn rootworm (Diabrotica spp.) or European corn borer [Ostrinia nubilalis (Hübner)] pressure exists, hybrids with transgenic resistance to these pests can have increased stress tolerance than those without, and thus may require higher plant densities to maximize economic return. Experiments were conducted from 2003 to 2005 following soybean [Glycine max (L.) Merr.] across three locations in Illinois, with the purpose of evaluating corn response to plant density for near-isoline hybrids with no insect resistance, resistance to corn rootworm, and resistance to both corn rootworm and European corn borer. At the same time in Iowa, corn response to plant density was evaluated over three site-years following both corn and soybean for a hybrid with resistance to European corn borer and the near-isoline hybrid with resistance to both European corn borer and corn rootworm. Root and stalk lodging were rare and nodal root injury was low in all experiments. Across site-years in Illinois and in both crop sequences in Iowa, there were quadratic responses of both corn grain yield and economic return to plant density, and these responses were similar among hybrids. Plant densities necessary to obtain economic returns within $2.50 ha^-1 of the maximum ranged from 82,300 to 89,700 plants ha^-1 in Illinois, 88,300 to 96,200 plants ha^-1 for corn following corn in Iowa, and 87,700 to 93,700 plants ha^-1 for corn following soybean in Iowa. These data suggest that in high-yielding environments where stress from corn rootworm and European corn borer is low, higher than normal plant densities are needed to maximize economic return, and that optimum plant density is similar for hybrids with and without resistance to these pests.