Source: Janet Knodel, Extension Entomologist, North Dakota State University
There has been a few reports of true armyworm (Pseudaletia unipuncta) feeding in wheat in the northeast region near Grand Forks and south central region near Wishek. There has been a lot of southerly wind flows, which can blow large numbers of armyworm moths into North Dakota from the southern states. Moths prefer to lay eggs in moist, shady areas and in small grains or grasses that have lodged or been damaged by hail or wind. Armyworms feed at night and hide under vegetation or in loose soil during the day.
The adult moth has a wingspan of about 1½ inch long. Forewings are brown with dull luster, and a white spot near the center.
Larvae are about 1¼ inches long when mature and prefer cool, wet weather. Larvae vary in color from green to brown with a dark stripe pattern running down the length of the abdomen on each side of the insect. There are three pairs of true legs near the head and five pairs of fleshy prolegs with a black band on the prolegs.
Larvae defoliate host plants. Young leaves will be completely eaten, and older leaves may be skeletonized leaving only the leaf veins uneaten. Often damage in a field may be spotty with field margins being the most prone to armyworm damage. In wheat, heads can be clipped. Outbreaks tend to occur following cool wet springs.
To scout for armyworm larvae in grains, part the plants and inspect the soil for fecal pellets. If pellets or feeding damage is found, look for larvae under plant trash, soil clods or in soil cracks.
The action threshold for armyworms in wheat is: Treat when 4 to 5 or more worms per square foot are present.
For insecticides registered in North Dakota for cutworm control, consult the 2010 Field Crop Insect Management Guide here.