Production Blog

Armyworm Alert

By Pam Smith , Crops Technology Editor

DECATUR, Ill. (DTN) -- The first alert for armyworm has been issued from the state of Missouri and growers across the Midwest are urged to begin scouting for the pest.

Wayne Bailey, University of Missouri entomologist, said in a news release Friday that most of the damage reports have come from the southwest corner of that state near Joplin and eastward. The pest has also been found in east central Missouri around Hermann and Montgomery City, according to Bailey.

Bailey said most of the damage to date has come in fescue fields, but wheat that is beginning to set heads is another potential target.

True armyworms have four pairs of legs at the mid-body. Young larvae are light green. Mature worms, about 1.5 inches long, are brown with long horizontal stripes.

The release indicates there's been some identity confusion with sawfly larvae, which do not cause economic damage and have legs the entire length of the body.

Bailey said early scouting to detect young armyworm larvae makes control easier. The immature worms feed at night, so scouting at dusk and early in the morning is better than at mid-day. Armyworm is also easier to control when small.

The economic threshold in hay fields is seven to 15 larvae per square yard.

Pam Smith can be reached at pam.smith@telventdtn.com

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