Iowa Fields at Risk for Corn Earworm

It’s that time of year again — when corn earworm moths are taking flight throughout the state. Here’s a little information on what to look for as you scout your fields for ear feeding pests like corn earworm.

What to look for

Corn earworms come in a variety of colors: light green, tan, brown, pink or nearly black. The caterpillar’s body is marked with light and dark stripes running lengthwise and the skin texture is coarse due to microscopic spines that cover the surface. Earworms are only in the ear for three to four weeks, but during that short time, they grow to nearly 1.5 inches in length.

Corn earworm can’t live through Iowa’s extreme winters, rather, the moths that lived and grew in southern states on either corn or cotton the year before are blown here during May and June each year to re-infest our state.

Because of the tightness of the husk around the ear, feeding is limited to the ear tip, resulting in small larvae or larvae that leave the ear before completing development. The presence of large numbers of eggs on fresh corn silks indicates the potential for damaging populations; eggs hatch in 5 to 7 days following egg laying.

Managing Corn Earworm

The first step to managing corn earworm is choosing a hybrid with built-in control against the pest to limit damage to both the leaf and ear. Early-planted crops are also most likely to escape peak populations of the egg-laying moths. Once larvae enter the corn ears, control with insecticides is difficult but can be effective with exact timing. One should direct insecticidal control towards young larvae that are feeding on the exposed eartips. Since larvae move down the silk channels as soon as they hatch, insecticides become ineffective once they move down from the eartip under the husk.