Western Corn Rootworm Adult Emergence has Begun

Western corn rootworm adult emergence is underway across east central Illinois. On July 1, Nick Tinsley, Research Specialist in the Department of Crop Sciences, observed his first adult male western corn rootworm of the growing season just south of Urbana within a University of Illinois research plot. Later that day, Joe Spencer, Associate Research Professor, Illinois Natural History Survey, observed five western corn rootworm adults after about 20 minutes of searching in his research plots north of Urbana. He noted very limited feeding had occurred already on some of the corn leaves. Joe estimated that initial adult emergence probably began 1 or 2 days earlier. It is important to recognize that adult emergence will occur throughout July and much of August. We routinely capture western corn rootworm adults in our emergence cages that are monitored several times weekly during this time frame. Injury to root systems will continue to take place through late July and into early August. Most of the intense root damage is likely to unfold by mid-July — a point at which we will begin our annual root injury evaluations.

Don’t be surprised in the coming weeks if you begin to see some lodging in cornfields. Much of Illinois has had plentiful rain this season setting the stage for shallow root systems which could contribute to lodging if storms and high winds move through an area. Severe rootworm injury could exacerbate the lodging.

If you become aware of significant root damage in a field, please share your observations with me and in turn, I will pass along this information to the Bulletin readers.

Mike Gray