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Are We Experiencing "Delayed" Insect Problems?

June 7, 2002
With so much focus on the less-than-optimal weather and poor crop growing conditions, it's possible that some insect problems may not have been detected. Until very recently when the weather warmed up, the condition of the corn crop was not so great. A lot of the seedlings were somewhat yellow and didn't appear very hardy. However, virtually everyone wrote these symptoms off to cool, wet weather. In most instances, weather probably was the culprit. However, during the past week, I have learned that the crummy appearance of some of the corn may have masked some injury being caused by subterranean insects, primarily white grubs and wireworms, but also cutworms. The cool weather has enabled some of these insects to stick around a little longer than usual.

Warmer weather has encouraged more rapid growth of corn, so people should now take note of any corn plants that "just don't look right." The presence of wilted, discolored, or dying plants might be a sign that insects are feeding below ground. Dig around feeble plants to search for root-feeding insects (grape colaspis, white grubs) or insects that tunnel into stems underground (cutworms, wireworms). Any of these insects are capable of reducing plant populations, but only cutworms can be controlled with "rescue" treatments. (Refer to the next article, "Black Cutworms Causing Economic Damage in Some Areas," for more information about cutworms.) At this late date, replanting is not a very good option. Let's hope that stand reduction is not so severe that yield is significantly compromised.

I also have received several reports that insecticides applied to prevent injury by subterranean insects in corn are not performing very well. These reports of poor performance against some corn soil insects, especially white grubs, have been associated primarily with more recently registered products. I remind you that efficacy data for several of the newer insecticides (liquids and seed treatments) are limited, so the performance of these products has not been tested under a lot of environmental circumstances. So if you experience inadequate control, contact a representative of the company that manufactures or distributes the product. Hopefully these folks will stand by their claims of insect control.--Kevin Steffey

Author: Kevin Steffey

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

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