Impact of simulated corn earworm kernel damage on field corn yield

The first generation Bacillus thuringiensis (Bt) traits in field corn (ex. Monsanto’s YieldGard Corn Borer and Dow AgroSciences’ Herculex I) demonstrated minimal activity against corn earworm feeding on grain in ears. However, the newer transgenic Bt corn hybrids express traits with significant efficacy against corn earworm and fall armyworm infesting corn ears.  Preliminary evaluations have demonstrated that these traits are effective at reducing ear damage from corn earworm and fall armyworm.  However, corresponding increases in corn yield have not been consistently observed.  Studies were initiated during 2012 to determine what level of kernel damage is required to impact corn yield.  These studies were conducted using the AgriSure Viptera technology to minimize kernel injury from natural corn earworm infestations.  Individual ear were assigned randomly to the simulated damaged treatments which included 0, 3, 6, 9, or twelve kernel rows damaged.  Damaged treatments were imposed at the milk stage to avoid interference with pollination.  The first kernels from the tip that would mature were estimated on each ear and the number of rows to be damaged began at that point and proceeded toward the base of the ear.  Kernels were damaged manually with a sharp object or finger nail.  All of the kernels damaged on an ear were counted and recorded.  After damage was imposed each ear was surface sterilized with 95% ethanol and covered with a corn ear pollination bag to minimize fungal growth.  At harvest each ear was hand harvested and shelled individually.  Grain weight, moisture content, and number of harvested kernels per ear was determined.

A significant relationship between kernel damage and yield was observed.  Based on the regression equation for every kernel damaged ca. 0.37g of grain yield was lost.  Additional studies are planned for the 2013.