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Elevated numbers of true armyworm moths are being captured in traps along the western side of the state. Highest numbers have been reported by MU extension agronomist Jay Chism in Barton county. It is unknown whether this population of moths will result in economic infestations of larvae, but the potential does exist. Migrating adults from more southern states or moths produced in Missouri from overwintering pupae often select grass pastures, wheat, fescue seed fields or occasionally field corn as their preferred egg laying sites during early spring. In most years three to four generations of true armyworm are produced in Missouri. First generation larvae typically damage field crops with later generations attacking grass lawns. In some years this insect will feed only on plant foliage, whereas in other years armyworms may feed on foliage plus cut seed heads from both tall fescue plants and wheat. Tall fescue seed fields are generally first attacked followed by wheat fields when armyworm populations reach outbreak levels. Rank or dense fields of grasses or wheat are common infestation sites for this pest.

True armyworm moths have grayishbrown to tan forewings each with a white spot in the center and grayishwhite hind wings. Eggs are greenishwhite in color, but darken just prior to hatch. Young larvae are pale green in color but change to dull greenishyellow to brown as they grow. Larvae have smooth bodies with three dark lines running the length of the worm (one on top and one down each side). The main identifying characteristic for true armyworm larvae is the presence of a dark triangle or spot located on the outside of each of the four pair of prolegs (legs found near the center of the caterpillar's body). The head capsule is greenish-tan and mottled with darker brown coloration.

Producers should scout tall fescue forage, tall fescue seed, and wheat fields to determine if armyworm larvae are present in economically damaging numbers. Scouting for armyworm is best done at night or during early morning. Armyworm larvae are nocturnal (night) feeders and generally remain hidden during bright, sunny days. Larvae typically feed on foliage from the soil surface upward. This often results in the canopy of an infested fescue field looking normal on one day and disappear the next as larvae complete their feeding on the host plant by consuming the remaining upper foliage. Larvae grow to about 1.5 inches in length, and often move from field to field as each food source is exhausted. Treatment is warranted when an average of four or more nonparasitized, half-grown or larger worms per square foot are present during late spring and before more than two-three percent of the heads are cut from fescue stems or wheat. In some years it may be necessary to control armyworm in grass pastures not used for fescue seed production. If defoliation of grass pastures by armyworm reach levels where control is needed, insecticides labeled for use against armyworm in grass pastures are the same as those for fescue.