Department of Entomology

College of Agriculture and Life Sciences

Corn Earworm

Biology. The corn earworm (Helicoverpa zea Boddie) is a common insect in corn. First generation caterpillars attack the whorl stage while the second generation is largely found in corn ears. Corn earworm larvae generally infest the ear through the silk and in years with heavy insect pressure, there can be multiple penetration sites. In this case, more than one larva may be found in an ear. However, since this caterpillar regulates its abundance through cannibalism (Barber 1936) it is unusual for more than one earworm larvae to be found in a whorl or ear.

Injury and damage. 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, is generally 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. There are now several events that have been incorporated into corn which target corn earworm and other lepidopteran pests, such as fall armyworm. These include the brands Genuity VT Triple Pro, Genuity SmartStax, and Agrisure Viptera. A list of the different Bt corn products and their efficacy for corn earworm, as well as other corn insect pests, can be found in Table 3 (pp. 7-8) of the Alabama Cooperative Extension corn IPM guide (Flanders 2010).

Under some circumstances Bt corn will also reduce 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 transgenic Bt corn and a 2010 result). Stress at the time of pollination probably has the greatest effect and this is an area of intense research.

In its 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 because this is where second generation of larvae, which infests corn ears, builds up population abundances. As moths, these insects fly to other crops to deposit eggs.

Barber, G. W. 1936. The cannibalistic habits of the corn earworm. U.S. Dep. Agric. Technical Bulletin No. 499: 1-19.

Flanders, K. L. 2010. Insect Pest Management, pp. 1-32. In IPM corn insect, disease, nematode, and weed control recommendations for 2010. Alabama Cooperative Extension System. 2010 IPM-0428.

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Current research and updates are performed by Dr. Dominic Reisig (Extension Entomologist) and Steven Roberson (Research Specialist). Based on original material of Dr. John Van Duyn (Extension Entomologist, Emeritus).
Information may be used with proper citation