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Be Alert for Cutting of Corn Plants by Black Cutworms in Southern Illinois

April 27, 2001
As indicated in last week's issue of the Bulletin (no. 4, April 20), we projected that cutting of corn seedlings in southern Illinois counties could begin as early as April 20. For central Illinois counties, cutting of corn plants is possible by the first week of May. In troubleshooting fields for suspected cutworm problems, it is helpful to assess the stage of black cutworm development. This will enable you to determine the number of days that cutworms are likely to continue feeding within a field and estimate the potential number of plants that may be cut. Figure 1 is a true-to-scale guide that can be used to improve your cutworm-management decisions.

To use this guide, grasp a cutworm larva tightly behind the head. Hold the head flat against the card. Look only at the width of the head capsule. Move the head down the scale until it matches the width of a bar. The number corresponding to that bar is the instar of that cutworm. After determining the instar (larval-growth stage), use the chart to estimate the approximate days left to feed and the potential number of plants that may be cut. For example, if the average size of cutworm larvae in a field is sixth instar, these cutworms will feed for about 14 more days and may cut one to four plants each, depending on the stage of corn-plant development. This information should help you determine the need for a rescue treatment.

Insecticides that are labeled for use as rescue treatments for black cutworms include Ambush (6.4 to 12.8 oz. of product per acre), Asana XL (5.8 to 9.6 oz.), Capture 2EC (1.47 to 2.2 oz.), Lorsban 4E (1 to 2 pt.), Pounce 3.2 EC (4 to 8 oz.) and Warrior (1.92 to 3.2 oz.). Each of these products is a restricted-use insecticide, and applicators must be certified.--Mike Gray

Cut corn plant and black cutworm.

Author: Mike Gray

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

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