Corn Earworm

John Van Duyn, North Carolina State University, Entomology Extension Specialist

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Corn earworm moth,larva,and pupa
Corn earworm larva from corn whorl
Corn earworm larva and damage from sweet corn ear
Last stage corn earworm larva exiting ear on way to soil
Corn earworm prepupa in earthen cell
Corn earworm pupa in soil

The corn earworm (Helicoverpa zea) is a common insect in corn. First generation caterpillars attack the whorl stage while the second generation is largely found in corn ears. Since this caterpillar is highly cannibalistic it limits it's own populations and is unusual for more than one earworm larvae to be found in a whorl or ear.

Whorl stage infestation is common but seldom reduces grain or silage yield. Usually the highest infestation will be found within the largest corn (usually earliest planted) in an area, but populations seldom reach a threshold level. Economic damage does not occur when less than 50% of the plants are infested. If treatment is warranted, insecticides may be moderately effective if applied from a ground sprayer. However, when caterpillars are deep within the whorl, results may be marginal. Aerial application is not effective (see Scouting for whorl feeding insects and North Carolina Agricultural Chemicals Manual

Ear feeding is common in most corn fields, with 60% to 100% of the ears having a single caterpillar in years of high populations. Also, secondary ears may be infested. Yield loss in typical field corn, however, is low, ranging from 3% to 5%, although it may be somewhat higher in white corn, popcorn, and corn grown for hybrid seed. Chemical control of corn earworm in the ear is difficult, requiring multiple insecticide applications, and is not economically justified in field corn. The Yieldgard brand of Bt field corn will reduce corn earworms by about 75% and limit the feeding of those that do survive. Under some circumstances Bt corn will also reduct the amount of mycotoxins (e.g. fumonisins and aflatoxins) in the grain by limiting feeding damage to the ear. However, this relationship is weak and during conditions favorable to ear-infecting fungi the Bt corn often shows no advantage (see Transgentic Bt corn).

In it's third generation, corn earworm is the most economically important insect pest in North Carolina and attacks a variety of crops in late July and August (cotton, peanuts, sorghum, soybeans, vegetables, and others). Field corn plays a critical role in the seasonal history of this pest as the second generation, which infests corn ears, realizes a great population increase and, after turning into moths, these insects fly to other crops to deposit eggs.

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This page ( was created by John W. Van Duyn Ph D. Extension Entomologist, Wayne Modlin, Res. Tech. III, and Steven Roberson.

Date Created 1/30/01.
Last revised on 10/31/03.

Published by North Carolina Cooperative Extension Service

Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

Caution: The information and recommendations in these Notes were developed for North Carolina conditions and may not apply elsewhere.