No. 12 Article 5/June 15, 2007

Insect Catch-All

With all of the focus on "headline" insects in corn and soybeans, lots of other insect activity is still worth noting:

European corn borers. Moth flights have been quite noticeable in several areas of the state, and larval injury, although maybe not economic in many fields, seems rather widespread, especially in southern counties. Randy McElroy with Monsanto Company examined many non-Bt corn fields in a broad loop through southern Illinois during the week of June 4, and he was most surprised by the consistency with which he observed whorl-feeding injury. He found few fields where the injury was cause for serious concern, but he found some injury in almost every field he examined. We should be thinking right now about the potential for larger densities of second-generation European corn borers than we experienced in 2006.

Grape colaspis. Corn fields injured by grape colaspis are numerous, more numerous than they have been for several years. We have written several articles about this situation in previous issues of the Bulletin, so we will not elaborate. We just want to keep this problem on our radar.

White grubs. There have been fewer reports of corn fields injured by so-called "true" white grubs (Phyllophaga species) than by grape colaspis larvae, but there have been some reports of significant injury. Kevin Nelson with Utica Elevator Company observed serious damage caused by true white grubs in a field in LaSalle County. The non-injured corn was in the V6 and V7 stages of development, but the plants injured by white grubs were severely stunted, with characteristic purpling of the stems. In some areas of the field, the stand was significantly reduced.

White grub larva (photo courtesy of Kevin Nelson, Utica Elevator Company).

Area of cornfield in LaSalle County severely injured by white grubs (photo courtesy of Kevin Nelson, Utica Elevator Company).

On a related note, entomologists at Purdue University have identified another white grub heretofore not known to cause injury to corn in the Midwest--the Asiatic garden beetle. They have written an excellent article with some really good photographs in the June 8, 2007, issue of their Pest & Crop newsletter. A new pest of future concern in Illinois? Well, we have one more pest to watch out for.

Burrower bugs. We continue to receive reports of corn fields with stunted plants that are infested with burrower bugs. I wrote about this pest in issue no. 11 of the Bulletin (June 8, 2007). Since then, we have confirmation of a few more incidents, always with the comments that "the ground appeared to be moving." We still are not certain about the relationship between stunted corn and this insect, but as I stated before, the association seems suspicious.

Twospotted spider mite. I hate even mentioning this pest, but when conditions are hot and dry, its occurrence should not be unexpected. John Fulton, University of Illinois Extension director in Logan County, reported finding twospotted spider mites in soybean fields in his county, with numbers building, although there are no symptoms of injury. Obviously, the situation bears watching.

It's mid-June, and heck seems to be breaking loose in some areas. But continued vigilance will keep us and everyone else aware, so keep your reports coming.--Kevin Steffey

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