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Western Corn Rootworm Emergence Delayed

July 17, 2003

Jared Schroeder and Nathan Wentworth, graduate research assistants in the Department of Crop Sciences, reported that the emergence rate of adult western corn rootworms has "picked up" this week. Even though emergence is well under way, it is delayed compared with recent years. Typically, we begin our evaluation of soil insecticides in mid-July. This year, we intend to begin our assessment of product performance (traditional granular products, seed treatments, transgenic hybrids) during the last week of July. We have indicated many times in previous issues of the Bulletin that added pressure is placed on soil insecticides when planting occurs in early April and the larval feeding period is extended through mid- to late July. This scenario is occurring in many areas of central Illinois. Shawn Jones, field sales agronomist with Pioneer, recently observed that severe root injury and lodging had occurred in a first-year cornfield located in Moultrie County. The field had numerous western corn rootworm adults and had not been treated with a soil insecticide at planting. Shawn also observed severe root injury and lodging in a first-year cornfield located in Macon County (west of Highway 51). This field was not treated with a soil insecticide at planting.

In August, we intend to conduct a survey of first-year corn rootworm larval injury in more than 30 counties of Illinois. Ten rotated cornfields per county are selected at random, and five roots per field are evaluated for injury. We organized a similar survey last year. Root-injury data in 2002 clearly indicates that the likelihood of first-year corn rootworm larval injury continues to creep westward each year. We are interested in learning of confirmed cases of larval injury in first-year cornfields, especially in western and northwestern counties of the state. So please pass along your observations from the field.--Mike Gray

Author: Mike Gray

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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