Erratic Armyworm Outbreaks Require Careful Scouting

Many entomologists say armyworms typically move from weedy grasses and small-grain cover crops to damage nearby corn.

Pictured Above: LARVAL LOOKALIKES. While the two larvae look very similar, the characteristic inverted “V” or “Y” on the head of the fall armyworm (bottom) sets it apart from the true armyworm (top). Both species primarily feed on other crops but can do significant damage to corn if the circumstances are favorable. The small white ovals on the true armyworm are the eggs of parasitic wasps or flies and could be a cue that treatment isn’t needed

The so-called “true armyworm” is one of the more frustrating early-season pests no-till corn growers encounter periodically, particularly if they are planting into small-grain or other grassy cover crops, or in fields near sources of grassy weeds.

The springtime pest should not be confused with the “fall armyworm,” another corn insect species which can become a problem later in the season, usually on late-planted fields. While neither pest usually causes widespread geographic damage to corn, localized areas can be devastated as they move from their grassy host plants into corn fields.

Ohio State University entomologists say true armyworm moths overwinter and then migrate northward from the southern U.S. and Gulf Coast in April and May — easily reaching Midwestern and northern corn-growing areas. While the pest does not overwinter in the more harsh winter climates of the northern U.S., annual migrations of moths are present each year.

The true armyworm (Pseudaletia unipuncta) attacks grass crops like cereal crops and seedling and whorl-stage corn. Entomologists say it is always associated with the presence of…

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Dan crummett 0618

Dan Crummett

Dan Crummett has more than 35 years in regional and national agricultural journalism including editing state farm magazines, web-based machinery reporting and has an interest in no-till and conservation tillage. He holds B.S. and M.S. degrees from Oklahoma State Univ.

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