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Department of Entomology

Department of Entomology
123 W. Waters Hall
1603 Old Claflin Place
Kansas State University
Manhattan KS 66506-4004

785-532-6154
785-532-6232 fax
entomology@ksu.edu

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Corn Insects

Black Cutworm, Agrotis ipsilon.

For detailed information on black cutworm please see KSRE publication MF2954:  Black Cutworm.

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Full grown black cutworm larva.

Black cutworm damage is usually restricted to the first two weeks following planting. The appearance of leaves with scattered transparent “windows” or notches chewed out of the sides indicates small larvae may be present. Frequently, however, this subtle damage goes unnoticed. Larger larvae can sever plants. Early reductions in plant stand will result if the growing point has been killed. Preplant or planting-time treatments for cutworms usually are only justified when severe perennial problems occur. Rescue treatments (applied postemergence) are almost always preferred over preventive treatments that are typically applied before or at planting. Refer to Part II of this publication for assistance in postemergence situations. Note that corn hybrids with Herculex I Insect Protection are resistant to black cutworm damage and thus provide another management option for this pest. In addition the new seed treatments containing thiamethoxam (Cruiser) and clothianidin (Poncho) also are labeled for cutworm suppression and their use should be taken into account when planning black cutworm treatment options.

Cutworm problems may occur statewide, but develop to more serious levels in eastern Kansas. Problems in Kansas are much less frequent than in corn production areas to the east. Conditions often associated with cutworm problems include early spring weed cover prior to planting, which often is associated with late wet springs, nearby permanent vegetation, corn following soybeans, and reduced tillage. However, regardless of conditions, if an adequate egg-laying moth flight does not develop, cutworm problems will be nonexistent. This is a major reason that rescue treatments rather than preventive treatments are recommended.

Cutworm-susceptible fields should be scouted frequently for damage from the start of plant emergence until the corn is 6 to 8 inches high. The application of a rescue insecticide treatment may be justified if 3 to 5 percent of plants in the two-leaf stage are being cut and the majority of the worms are ½ inch or less in length. Each cutworm has the potential to cut from four to six plants at the two-leaf stage. Action should be taken at lower levels of stand loss under cool conditions and smaller plant developmental stages. On the other hand, warm conditions and larger plants reduce the damage potential per cutworm. Control attempts when the majority of the cutworms are ¾ to 1 inch in length may give poor results. The alternative is to wait at least two weeks to give the worms a chance to mature and pupate, then replant where necessary.

Please refer to the most recent version of the Corn Insect Management Guide for treatment options. 

Page last updated 11/02/2013 by J.P. Michaud.