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Issue No. 12, Article 7/June 10, 2005

Subterranean Insects Still Causing Headaches in Cornfields

I have been remiss in sharing some of the reports we have received about belowground insects causing problems in cornfields around the state. As if the weather and soil conditions haven't been tough enough on corn plants, a host of secondary insect pests of corn have caused problems here and there this spring. Undoubtedly, the slow emergence and growth of corn and the cooler-than-normal temperatures have enabled these pests to feed for an extended period this spring. Following are thumbnail sketches of some of the reports we have received.

Wireworms

Far and away the most frequently reported subterranean insect pests of corn this spring have been wireworms. Although white grubs and grape colaspis have taken center stage in the past, wireworms are having their year. Several people have reported heavy infestations of wireworms causing significant stand reductions. And as we have reported in the past, some of the infested fields had been treated with an insecticidal seed treatment or a soil insecticide. Apparently in these instances, the products did not work as advertised. Kevin Black, with Growmark, reported that there have been "numerous reports" of insecticidal seed treatments (Cruiser, Poncho, Latitude, Kernel Guard) not adequately controlling cutworms, seedcorn maggots, white grubs, and wireworms.

White Grubs

Ryan Stoffregen, with Advanced Crop Care in Kingston, Illinois, reported finding white grubs causing significant injury in several fields of corn planted after wheat. The affected fields were in Boone, DeKalb, and McHenry counties. In some of the heaviest infestations, Ryan found two to three grubs per plant. Again, some of the affected fields had been treated with soil insecticides.

Southern Corn Leaf Beetle

Shawn Jones, with Pioneer Hi-Bred International, observed southern corn leaf beetles causing noticeable injury in a field in Pike County during the last week of May. The numbers of beetles were fairly large in isolated spots within the field, and the injury was fairly severe.

Grape Colaspis

I checked some of the previous years' issues of the Bulletin and learned that grape colaspis problems usually are detected toward the end of May and into the first half of June. Consequently, it's not surprising that some growers have had the misfortune to encounter these pests recently. On June 2, Robert Bellm, Extension crop systems educator in Edwardsville, observed significant grape colaspis injury in a field of corn planted after red clover in Clinton County. The symptoms were classic--stunted, wilted plants with leaves with "burned" edges. In some spots in the field, the stand looked puny, at best.


Corn seedlings injured by grape colaspis larvae (photo courtesy of Robert Bellm, University of Illinois).


Clinton County cornfield with symptoms of grape colaspis injury (photo courtesy of Robert Bellm, University of Illinois).

Some rain would alleviate the extent of the injury caused by many of these secondary insect pests of corn. Unfortunately, when corn growth is adversely affected by environmental conditions, insect injury is exacerbated.--Kevin Steffey

Author:
Kevin Steffey

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