Scientific name: Helicoverpa zea
Order: Lepidoptera
Family: Noctuidae

Info

Biological Description

• Moths: Sand-colored with many dark blotches. Forewings have a large dark spot halfway between the body and the wing tip, and a wide, dark band near the outer wing edge. Hindwings have dark veins and a wide dark band near outer wing edge.
• Larvae: Newly hatched larvae are creamy white with a black head. Larvae go through five to six instars, reaching up to two inches in length. Larger larvae vary in color and can be yellow, brown, red, and green. Three or four prominent bands along the length of either side of the larvae can be cream, pink, green or yellow in color. The head is usually dark yellow or orange.
• Eggs: Tiny, flattened spheres 1/32 inches in diameter, and ribbed. Eggs are white to light yellow at first, but turning a dusky brown before hatching.

Economic Importance

• Corn earworms primarily cause economic damage to fresh market and processing sweet corn and hybrid dent seed corn.
• Susceptible crops:
  • Other susceptible crops include field corn, tomatoes, lettuce, peppers, and snapbeans.

Life Cycle

• Most corn earworms in Wisconsin migrate north from the Gulf States.
• Adults appear in the state in June and July, with peak flight in August and September.
• Eggs are laid singly and are usually deposited on newly emerged silks, but they may also be laid on upper and lower leaf surfaces, stalks, tassels, and husks.
• Eggs hatch in 1 to 8 days
• Larvae are cannibalistic, so usually there is only one found per corn ear.
• Generations:
  • There are two generations per year in Wisconsin
  • The first generation adults usually arrive in late June and pose a problem in very early sweet corn.
  • Second generation appears in mid-August to early September and causes more damage.

Damage/Symptoms

• Damage is a result of larval feeding.
• Larvae feed on leaves, tassels, silks, and developing kernels.
• Small larvae can cause pinhole feeding injury on leaves.
• Large larvae can cause severe defoliation.
• Most of the economic damage is due to ear feeding. Larvae feed in the tips of ears.
• Secondary pests and microorganisms can cause damage to ears after initial corn earworm feeding.

Scouting Procedure and Economic Threshold

• Pheromone traps are the best technique for monitoring corn earworm populations. Pheromone trap catches of 5 to 10 moths per night for three consecutive nights indicate that moths are likely laying enough eggs to warrant treatment of fields, if corn is in the vulnerable stage between the brush stage and silk browning.
• Blacklight traps can also be used to monitor populations, though they collect fewer corn earworms. Consider treatment when blacklight traps catch 3 to 5 moths per night for three consecutive nights if nearby fields are in the vulnerable stage.

Integrated Control

• Biological Control: Several beneficial insects attack corn earworms. Trichogramma wasps as well as chalcid and braconid wasps parasitize earworm eggs. Minute pirate bugs feed on eggs.
• Chemical Control: Treatment timing is critical because once earworms get inside the corn ear, they are protected from insecticides. Insecticides must be present on corn silks when eggs hatch. For current Wisconsin recommendations, consult University of Wisconsin-Extension Bulletin #A3646, Pest Management in Wisconsin Field Crops.

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Site Links

Insect Images

• Corn pest images

Extension Publications

• Moth Identification Guide for Blacklight Trap Catch in Wisconsin
• The Corn Earworm

Wisconsin Crop Manager Articles

• Section 18 for Coragen, for Corn Earworm, Sweet Corn. Wisconsin Crop Manager, Vol.15 No.20, July 24, 2008. Cullen, E.

PowerPoint Presentations

• 2007 Pest Management Updates, Slides (34-35). 2007. Cullen, E.

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