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Scouting Corn for the Cutworm Feeding

University of Minnesota Extension, Stearns County News
June 1, 2016          
Released by:  Dan Martens, Extension Educator
University of Minnesota Extension
Stearns, Benton & Morrison Counties

Release Date:  June 6, 2016

Source:  Bruce Potter, Extension Specialist

Scouting Corn for the Cutworm Feeding

FOLEY, Minn. (05/27/2016) — Extension colleague Nathan Winter shared this summary of information provided by Extension Specialist Bruce Potter:

Cutworms are nocturnal. During the day, they hide under soil clods, crop residue and loose soil. Cutworms will likely be deeper when soils are dry. Carefully look under pieces of residue and soil clods close to cut or injured plants. If you don’t find a cutworm near the base of an injured plant, look near a couple plants on either side in the row. Do stand counts in areas of the field with damage and note the percentage of plants with leaf feeding and those cut. To help with your decision, you can flag areas of row within in the field and return the next day to determine if damage is ongoing.

Bruce Potter, University of Minnesota Extension IPM Educator indicates that cutworm’s infestations in small corn (3 leaf or less) require more aggressive management than large corn. Don't give up on scouting too early. Late instar black cutworms can kill up to 6 leaf corn by burrowing into the growing point.

Cutworms reduce corn yield by decreasing final stand or plant population. The generic economic threshold for black cutworm in corn is 2 to 3 percent of the plants cut or wilted when the larvae are less are than ¾ inch long. The threshold increases to 5% cut plants when larvae are larger. Thanks, Nathan.

I’ll add that crop consultant Rick Gilbertson reported some Black Cutwork damage in a corn field in Benton County. This was an alfalfa field in 2015 that was tilled in the fall with some plants escaping tillage. This might have been an isolated incident, but it’s good this time of year to check fields for many reasons.

Black Cutworms don’t survive winters in Minnesota. Moths come up each spring with weather systems from the south. Moth traps indicated way more moths coming in this spring. Weedy patches in fields can be attractive for egg laying. Larvae feeding in the Benton County field could fit with a moth flight that occurred about March 28. Do an Internet Search for “Minnesota Extension Crop News” for more details provide by Bruce Potter.

You’re also welcome to call the County Extension Office for help in getting more information - Benton 968-5077, Stearns 255-6169, Morrison 632-0161.


Daniel Martens
Extension Educator, Ag Production Systems
(320) 968-5077
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