The Danger of Army Worms

Army worm damage in a corn field.
Army worm damage in a corn field.

These pictures illustrate army worm damage on a corn field in northern Clark County.

Army worms do not over winter in Wisconsin, moths migrate up from the south, mate and lay eggs in grass fields. Army worms, once here can have a second generation, usually appearing in July, and a third generation may also appear in September.

Army worms attack grasses, so small grains and corn are susceptible to infestation. The presence of grass weeds will attract moth’s to lay eggs. The field above was sprayed late post-emerge, likely after moths had laid their eggs in the grasses. Corn damage will first appear as jagged leaf edge feeding, then as the infestation increases feeding moves inward until eventually only the mid rib of the plant remains. Worms mostly feed at night or on cloudy days but can often be found hiding in the whorls on sunny days. Worms are brownish-green with alternate light and dark stripes down their backs. A full grown worm is about 2 inches long.

Devastation caused by army worms.
Only the center rib remains of most of these corn leaves.

Insecticide is an effective treatment when infestation occurs. Cultural practices such as good early season weed control, tillage, and planting certain traited corn can often prevent an outbreak from ever occurring. It is important to keep an eye out for army worm infestations, if they are caught early enough damage can be kept to a minimum with a timely pesticide application.

*Update: Army worm damage has now also been verified in east central Clark County.
**Update: Army worm damage has been found throughout the Clark County, mainly in fields sprayed post emerge that had higher weed pressure.

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