Posted on Sep 2, 2015 by Michael Gray

Western Corn Rootworm Densities Far Below Average in Illinois Corn and Soybean Fields

As part of a USDA National Institute for Food and Agriculture (NIFA) sponsored grant, surveys of insect pests were conducted in randomly selected corn and soybean fields across 28 counties throughout Illinois this summer. Fields were sampled during two discrete periods: July 27 – July 31 and August 12 – August 24. Within each county, five cornfields and five soybean fields were sampled. Within a cornfield (away from the field edge and end rows), 20 consecutive plants were examined carefully for northern and western corn rootworm adults. In soybean fields, 50 sweeps of a sweep net were made in the field interior and another 50 sweeps were taken at the edge of a field (between the last two border rows). Within each cornfield, one leaf was obtained from one of the 20 corn plants examined for rootworm beetles. Each leaf was tested for the presence of Cry (Bt) proteins that are expressed to limit corn rootworm larval injury to root systems. Provided are the key findings.

Why are western corn rootworm densities so low?

Based on these survey data, can I safely assume corn rootworm pressure in my fields will be lower next year?

One of the key take home messages from this report should be the importance of regularly scouting your fields for key insect pests, especially the western corn rootworm. Having reliable scouting information on a field-by-field basis this year could pay dividends next season as producers face input decisions for 2016 in the coming months.

I offer my thanks to Nick Tinsley (Postdoctoral Research Associate, Department of Crop Sciences) and Alex Kaluf (Graduate Research Assistant, Department of Crop Sciences) for their leadership in the planning and conduct of this statewide survey. I also thank Luke Harvey and Tate Estes (Summer Interns, Department of Crop Sciences) for their hard work in sampling fields.

Mike Gray, Professor and Extension Entomologist and Nick Tinsley, Postdoctoral Research Associate

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