Fall armyworms are a risk to sweet corn and turf.
Fall armyworm caterpillars can be green, brown, or black with white to yellowish lines running along its back from head to tail with an inverted “Y” between the eyes. Another identifiable characteristic is four black spots in a square on the top of the segment near the back end of the caterpillar. Caterpillars are small at first (less than 1/8”); however, after feeding for about two to three weeks, they grow to be about 1" to 1.5” long.
The adult moths are grayish, with grayish, white hind wings and a 1-1/2-inch wingspan.
Damage Caused by Fall Armyworms
- Corn: Fall armyworm caterpillars feed in the whorl of late sweet corn crops but do not burrow into the stalk as does European corn borer. Damage to corn can appear as ragged-edged holes on leaves, tassels, or ears.
- They also feed on the kernels of the ear, commonly attacking the side of the ear through the shucks. The external entry point into the shucks can easily be missed, but the damage to the kernels and associated frass (fecal material) are obvious once the ear is shucked.
- They also feed on the kernels of the ear, commonly attacking the side of the ear through the shucks. The external entry point into the shucks can easily be missed, but the damage to the kernels and associated frass (fecal material) are obvious once the ear is shucked.
- Fields: In turf, hayfields, or pasture, the damage often appears as brown or burned-out patches and can often be confused with drought damage.
Life Cycle of the Fall Armyworm
Fall armyworms do not overwinter in Illinois but rather fly north each year. They most often arrive in southern Illinois in July and northern Illinois in August, though immigration can occur by June throughout the state.
Moths are more active at night feeding on nectar and depositing eggs. A female moth can deposit up to 2,000 eggs. After feeding, caterpillars tunnel about an inch into the soil and enter the pupal stage from which a moth emerges after about 10 days. From there, it will repeat its lifecycle.
Management of Fall Armyworms
Scouting in the cool part of the day when the caterpillars are actively feeding will allow you to determine the size and number of fall armyworm which will help decide control strategies. If you are not scouting when caterpillars are actively feeding, you will need to look deeper into the canopy either by parting grass or using a sweep net.
Turf: Insecticide applications are not usually economical for control of fall armyworm; however, infestations of three or more caterpillars per square foot may justify an insecticide application. Fall armyworm is best controlled when caterpillars are 1/2” or smaller. It is best to make applications early in the morning or later in the evening when larvae are most active.
Corn: Control fall armyworm during the late whorl stage and into the tasseling stage. Insecticide applications after silking has begun are not completely effective in preventing ear damage.
Contact your county Extension office for current pesticide controls.
Read more about armyworms at Good Growing: Fall armyworm numbers highest in 30 years in Illinois.