Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


Black Cutworm Update


Black cutworms do not overwinter in Iowa. Rather, black cutworm moths fly in from the south. If few or no moths fly in, then few or no eggs will be laid, and black cutworm will not be a concern. If a significant number of moths fly in, then there may be enough eggs laid to cause significant loss in a corn field. To monitor incoming flights of black cutworms, a series of traps have been established. Development of black cutworm is based on climatic temperature. Black cutworms develop whenever the temperature is above 51 degrees. Therefore, the stage of development is estimated based on Growing Degree Days (GDD) Base 51 since the moth flight, which is when eggs may have been laid. The formula for a given day is the daily high (minimum 51) plus the daily low (minimum 51) divided by 2 to determine the average temperature for the day. From the average temperature for the day, subtract 51. If the result is a positive number, add it to the GDD of all prior days with a positive result. (Note: Development used to be predicted on a GDD Base 50, but newer research suggests that Base 51 is more appropriate. This change will result in about a one day difference in the predicted onset of cutting.)

Black cutworms begin to hatch and feed at 300 GDD base 51 after the moth flight.

Note: Preventive treatments are NOT recommended. See pages 70-71 of the May 19, 2003 Integrated Crop Management Newsletter and the May 5, 2011 ICM News article. for details.

Note: Seed treatments may not provide adequate protection from black cutworms. See page 76 of the May 9, 2005 Integrated Crop Management Newsletter and the May 5, 2011 ICM News article. for details.

Projected first cutting dates and further information is available at this ICM News article. You may also want to follow the University of Illinois Bulletin and the Wisconsin Pest Bulletin.

Once 300 GDD have accumulated in the area, scouting should take place on all corn until it reaches the five-leaf stage (V5).

Start scouting fields about 2 days before the predicted first cutting as local conditions may have speeded up development.

When scouting, be sure to differentiate between Black Cutworms (Top) and Dingy Cutworms (Bottom) as Dingy Cutworms almost never cause an economic loss worth treating. See page 42 of the May 17, 2004 Integrated Crop Management Newsletter.

A dynamic action threshold, allowing the user to enter his/her own cost of management and price of grain, is at Dynamic Black Cutworm Action Threshold at the Integrated Crop Management News.


If you have any questions, please feel free to contact the Iowa State University Extension Office.
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Last Update: May 11, 2017
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