Multiple generations of fall armyworms occur each year. The damaging life stage, larvae, live for about two weeks but this can change based on temperature. Small larvae do not each much for the first ten days of their life; the larger life stage causes almost all of the damage during the last couple of days before pupation. Smaller larvae are easier to control than larger ones.
Fall armyworms are notorious for having a broad host range, and you may find populations in home lawns, turf, field crops, and pastures. Infestations are especially common in well-managed bermudagrass. Two distinct features identify fall armyworms. The head has light markings that form an upside-down “Y” (Figure 1) while the opposite end has four black dots that form a square (Figure 2).
Scouting is the best way to determine if and how many fall armyworms you have. Grasses can be inspected by getting on your knees and looking at the top of the grass blades during cooler parts of the day and down near the soil surface during the hotter parts of the day. A soap flush in turf may also be used to detect infestations. For row crops and forages, a sweep net is an easy method to sample for armyworms.
—Managing Fall Armyworms in 2021, Katelyn Kesheimer and Scott Graham, Alabama Cooperative Extension System
Information below has been gathered from Ohio State University State, Field, and Extension Specialists.