Joe Spencer, Associate Research Professor, Illinois Natural History Survey, indicates that his research crew observed a male western corn rootworm adult in his plots northeast of Urbana on June 26. Males generally emerge before the females. Earlier today (June 27), Joe and his students found five western corn rootworm adults in refuge corn. It took them about 1 1/2 hours to find these beetles, so, emergence is just underway. In addition, Joe has found significant root injury on several of the refuge plants. This should not be alarming — recall the purpose of refuge plants is to create survivors in fields to prolong the usefulness of Bt hybrids.
By the July 4th holiday, I anticipate many reports of western corn rootworm adults in producers’ fields. Although much of the state has experienced plentiful precipitation this spring and early summer, soil conditions during larval hatch (late May, early June) were generally favorable for corn rootworm survival. Simply put, ponded areas of fields were less common in many areas of Illinois during this time frame. These conditions will likely work in favor of corn rootworms. We anticipate our annual root evaluations to begin the week of July 14. I encourage producers to look for signs of root injury, such as lodged plants, and take the time to dig up some plants and evaluate the root protection afforded by their product (Bt hybrid and/or soil insecticide) of choice. With input costs rising and commodity prices less favorable, producers increasingly need to make informed corn rootworm management decisions for 2015 and beyond.