Feeding damage during the early flowering stage can be extensive. Extensive feeding on the flowers will delay plant maturity, cause the crop to develop unevenly and significantly reduce seed yields. When plants are fully podded and leaves begin to wilt or die in late July or early August, larvae will remove the surface tissue from the stems and seed pods. The seeds within a damaged pod will not fill completely and pods may shatter. Larvae may also chew into seed pods and eat the developing seeds.
Crop damage is usually first evident on plants growing on ridges and knolls in the field.
Damage can only be prevented by early field monitoring and the application of insecticides, if larval numbers exceed the action threshold. The presence and relative abundance of the diamondback moth can be determined by using pheromone traps. These traps cannot predict the potential for crop damage, but trap counts can provide an early warning of a possible infestation. Environmental conditions will determine how many eggs are laid and whether the larvae emerge and survive. To obtain an accurate count, repeat this procedure in at least five locations in the field.