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Armyworms on Field Scouting List
Armyworm outbreaks in North Dakota can occur when large migrations of moths from southern states occur in late spring and early summer. Moths prefer to lay eggs in moist, shady areas where small grains or grasses have lodged or been damaged by hail or wind. Armyworms feed at night and hide under vegetation or in loose soil during the day.
We are at the time of year when armyworm moth flights could occur in the region.
Armyworms are olive-green or greenish-brown with dark stripes running the length of the back along with two orange stripes on each side of the body. Larvae range in size from 1/4 to � inch long. The eggs look like small white beads and are in masses. Eggs hatch in about eight to ten days.
During the day, armyworms can be found under plant trash, clods of soil and in soil cracks. They feed at night. Smaller worms will feed on lower leaves. As they increase in size, they tend to feed higher up on the plant. They feed for about three to four weeks.
Sampling for armyworms should include inspections at five locations using an X pattern to spread the sample sites out across the field. To scout for armyworms in grains, part the plants and inspect the soil for fecal pellets. If pellets or feeding damage are found, look for larvae under plant trash, soil clods or in soil cracks.
In small grains, treatment for armyworms is advised when four to five or more larvae are found per square foot. In corn, treatments should be applied when two or more larvae occur per plant on 25 to 30 percent of the stand.
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