Corn Earworm
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The corn earworm (Heliocoverpa zea) is the most serious sweet corn pest because it feeds directly on the tip of the ear. Once worms are inside the ear, control is impossible. Earworms are variable in color, but they have a brown head without markings and numerous microscopic spines covering their body, giving it a sandpaper-like feel. Female moths search out fresh silks on which to lay single eggs. Egg laying ceases when silks dry. Following hatch, the small larvae often eat the eggshell before beginning to feed on the silk and entering the ear. Corn earworms generally complete their development in 14 to 16 days. Full-grown worms leave the ear and pupate in the soil. Later-planted sweet corn is subject to intense earworm egg laying.
Corn earworm damage
(Photo: UK Vegetable IPM Team, University of Kentucky)
Color variation among larvae
(Photo: UK Vegetable IPM Team, University of Kentucky)
Corn earworm adult moth
(Photo: UK Vegetable IPM Team, University of Kentucky)
Management:
- Select sweet corn hybrids with good tip coverage and tight husks to limit earworm damage to the ear.
- Bt sweet corn can provide up to 90% control of corn earworm.
- To protect ears while the silks are fresh, use pheromone traps to monitor moth activity and determine frequency of sprays. Initial sprays for corn earworm should be timed to protect the ear when most ears show silk emergence.
- Later plantings will require more intensive earworm management.
- Corn earworm resistance to pyrethroid sprays may be an issue in certain areas/ times of the year.
- Planting early can help organic growers avoid corn earworm.
