Growers should scout fields for true armyworm. Cool springs are suitable for outbreaks. Prioritize scouting grass pastures, wheat and corn fields. In years past, problems have occurred in Platte, Clinton, Andrew and Gentry counties in grass pastures. However, a large flight was caught in MU Pest Monitoring Network in Holt County so Nodaway, Holt and Atchison County growers should scout corn fields and pastures.

The best time to scout for this insect is dawn or dusk as the larvae feed at night. During the day, they will hide at the base of plants under leaves and plant debris. Larvae can defoliate plants and as they become larger, the damage increases. Once they defoliate grass plants, they will move to other areas in a field or on to other fields.

Moths fly to grass fields and lay eggs. They do feed on legumes. Once eggs are deposited, larvae hatch in three to six days. The insect has seven instars or worm stages as they develop from egg to adult moth. There may be two to three generations per year.

The larvae of this insect are identified by the looking at the prolegs located in the center of the worm. These prolegs will have a dark brown to black triangle located on the foot of the proleg.

The economic threshold for control in pasture is three or more half-grown larvae per square foot.

Chemical control should target one-half inch long caterpillars with insecticides. Fully-grown larvae are one and one-half inch in length, will be close to pupating, and so do not treat.

During wet weather, caterpillars can have several pathogens such as bacteria, fungi which can reduce numbers. It is important to look for parasitized caterpillars when making a control decision.

You can sign-up for pest alerts at MU Integrated Pest Management site and subscribe to this free service at https://ipm.missouri.edu/pestMonitoring/

If you are having crop or pasture defoliation from this insect pest, contact Wayne Flanary, Field Specialist in Agronomy, University of Missouri Extension, office 816-279-1691 or cell 913-220-3670.