Use a 4 foot X 4 foot square to sample each site. You will want to record the number of armyworms present in each 4 X 4 area and the average length of the armyworms. When observing larvae check for parasitic eggs just behind the head. These small, oval, yellow eggs are of a fly parasite that will kill the larva. Avoid treating with insecticides when large numbers of larvae are parasitized.
Pheromone traps are available for monitoring adult armyworm activity.