It emerges in early spring, feeds on alfalfa shoots and migrates into new fields to lay eggs. All the adults are female. The eggs hatch into white legless grubs which feed on the main and side roots of the host plant. The grubs girdle the taproot or gouge its surface leaving deep spiral grooves. The total life cycle requires a span of two years.
Damage is most evident in late summer and early fall.
In the infested area wilted plants should be dug and checked for damage and the presence of grubs. Alfalfa is the preferred host but the grubs also attack clover and a number of weeds. Infected alfalfa fields should be plowed under and planted to corn, soybeans or cereals for three years to reduce populations. Armyworms Armyworms can occur in grasses in late June and July. If they become destructive, control them as indicated in Disease and Insect Control in Cereal Crops section.