Efficacy of Current Maize BT Traits Against Corn Rootworms in North Dakota

Field experiments were conducted to determine the efficacy of current Bt traits in maize (Zea mays L.) hybrids and soil-applied insecticide for corn rootworm (Diabrotica spp.) management. Experiments were conducted as a randomized complete block design with a split-plot arrangement. The whole plot was no insecticide or soil-applied insecticide. The subplots were different Bt maize hybrids and treatments: non-Bt (untreated control), seed-applied insecticide, Cry3Bb1, Cry34/35Ab1, and Cry3Bb1 + Cry34/35Ab1. Root injury was evaluated using the Iowa State University rating system. Hybrids expressing any Cry protein averaged 0.12 nodes pruned. Hybrids without Cry proteins averaged 0.37 nodes pruned. Seed-applied insecticide reduced root pruning compared to the untreated control. Both had greater root injury than hybrids with Cry proteins. Soil-applied insecticide did not always reduce root pruning. Hybrid yield and test weight were highly variable, depending on the hybrid?s genetics. This research indicates the Bt-traits tested are effective in managing corn rootworm.North Dakota Corn Utilization Counci