Evaluation of Transgenic Rootworm Corn, with and without Seed Treatments or Insecticide

Materials and Methods The corn was planted in an area that had been planted the previous year with “trap crop.” The seed planted for the trap crop was a mixed maturity blend with a greater proportion of late-maturing varieties. This trap crop constitutes a favorable environment for adult rootworm females late in the season when other fields are maturing and results in a high abundance of rootworm larvae the following year. The experimental design for this study was a split block design with four replications (i.e., blocks). Treatments were eight rows wide, to minimize border effects, and 75 ft long. The study was planted on May 9 by Ryan Rusk from the Northwest Research and Demonstration Farm at a population of 32,000 seeds/acre. The Poncho 1250 seed treatment was applied commercially on both hybrids tested. The insecticide, Aztec, was applied in furrow at an application rate of 6.7 ounces/1000 row-ft. Stand counts (Table 1) were taken by counting the number of plants in 17.5 row ft. The stand counts were taken both early and late in the growing season and averaged. After the majority of corn rootworms had finished feeding, five roots were dug per treatment from rows two and five. Prior to leaving the field, excess soil was removed. Roots were then soaked in water overnight, and subsequently washed with a pressurized water sprayer to remove the remaining soil. Roots were laid out by replication and evaluated for rootworm feeding injury (Table 2) following the Iowa State Node-Injury Scale (0–3). The percent product consistency was calculated for each treatment as the percentage of times a treatment limited feeding injury to 0.25 node or less. Lodging counts (Table 1) were taken at harvest time along with final stand count. A plant was considered lodged if it was leaning at least 30 degrees from vertical. Yields (Table 2) were taken by machine harvesting rows three and four from the plots. Weights were converted to bushels/acre of No. 2 shelled corn at 15.5% moisture.