The adult armyworms are rarely seen during the day but become active in the late-evening and night hours. The females lay eggs on the lower leaves of host plants, and feeding starts as soon as the new larvae hatch. True armyworm larvae feed at night and seek shelter during the day. The fall armyworm larvae remain active in daylight and night hours. Start looking for true armyworm outbreaks in early spring and for the fall armyworm from mid- to late July.
Check fields regularly during periods of armyworm activity.
For successful control and to prevent extensive damage, start treatment when you find five to seven small worms per square foot of surface area. The larval stage of the alfalfa weevil can be one of the most destructive insects to alfalfa stands. You can find larvae feeding on stem tips, on upper leaves as they unfold, and eventually on lower leaves. Severe losses of dry matter and a decrease in forage quality can result if you don't control this insect. Effective control requires a timely application of an approved insecticide based on number of larvae per stem.