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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

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Corn Insects

True Armyworm, Pseudaletia unipuncta.


When nearing maturity, armyworm larvae are 1½ to 2 inches long. The head capsules have honeycomb-like markings, and the body lacks obvious hairs. Overall body coloration varies, but is usually some shade of greenish-black with two alternating dark and orange stripes running lengthwise down each side plus a light or faint white line on the back. Adults frequently deposit their eggs where grass is very lush, often in low-lying areas on wheat or pasture ground. Field margins or fields with dense growths of grassy weeds also are preferred egg-laying sites. Problems develop when the larvae consume the grasses or the grasses dry (wheat matures) and the larvae move to corn to survive. Problems from this insect are expected to increase as more reduced tillage is practiced — especially if grassy weed control is not adequate. Later season damage is very characteristic: The larvae remove all of the leaf tissue except the midrib and work their way up the plant, defoliating as they go. Large numbers of small white cocoons near dried larval bodies indicate that the insects were killed by parasitic wasp larvae. If larvae are less than 1¼ inches long, treat when larvae are present on 30 percent of the plants with five to six extended leaves or when one larva per plant is present on 75 percent of the plants. Concern about yield loss during reproductive development is greatest if it appears that defoliation will approach the ear zone before hard dent. Lower thresholds may apply if the plants are under other stresses.

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.