Fall armyworms are making themselves known in many late-planted cornfields in southern Illinois. Approximately 1-1/4 inches long, these larvae vary in color from light brown to green and have three yellow stripes down their side. The fall armyworm can be distinguished from the true armyworm by a white or yellow inverted "Y" on the head of the fall armyworm.
Fall armyworm larva.
Inverted "Y" found on the head of the fall armyworm.
The fall armyworm is a migratory insect; moths overwinter in the southern states and migrate northward during the summer months and early fall. Moths lay eggs on corn leaves at night. Each egg mass may contain as many as 150 eggs. Larvae feed during the day in the whorl tissue or ears. Damage to the ear by the fall armyworm resembles injury caused by the corn earworm, except that an entry hole will be visible with fall armyworm injury.
Treatment for the fall armyworm is often questionable. Injury caused by the fall armyworm is predominantly cosmetic and rarely economic. Recommended thresholds for fall armyworm vary; a general recommendation found in the Illinois Agricultural Pest Management Handbook is to treat when 75% of the plants have whorl damage and the armyworms are still present. It's important to remember that treating for fall armyworms is difficult because of their placement in the whorl. Insecticide just broadcasted onto the foliage has little hope of controlling the worms, as they do not leave the whorl of the plant. To be more effective, insecticide needs to be directed into the whorl. Also, once the fall armyworm has entered the ear tip, treatment is ineffective. Insecticides labeled for control of fall armyworm are Ambush*, Capture 2EC*, Lorsban 4E*, Mustang Max*, Pounce 3.2EC*, and Tracer 4SC. Insecticides followed by an asterisk are restricted use pesticides. Please follow all label instructions.--Kelly Cook