August 1, 2022
Corn earworm is a common pest of field corn. It is the larva of the corn earworm that causes damage and it has one of the widest host ranges of any insect pest with over 15 cultivated plant hosts. Other common names include cotton bollworm, soybean podworm, sorghum headworm, tomato fruitworm, and vetchworm.
While they can cause damage during corn vegetative growth stages, it is rarely enough to warrant an insecticide application. Using general preventative pest management tactics, such as corn products containing Bacillus thuringiensis (Bt) proteins that target earworm, can protect the plant in both the vegetative and reproductive growth stages.1
Trecepta® corn can help to protect corn from a wide range of above-ground pests including corn earworm. If corn earworms have been a problem in your area, Trecepta® corn products are an option to consider.2
Identification
The larval stage can occur in a rainbow of colors, from green to dark brown (Figure 1). Other insect species, such as the larvae of fall armyworm, true armyworm, European corn borer, southwestern corn borer, and western bean cutworm, can also be feeding on corn. Each has distinct characteristics and feeding habits which can be used to help identify the pest.
Figure 1. Corn earworm larvae showing wide variety of pigmentation. Image courtesy of John Obermeyer, Purdue Extension Entomology.
Life Cycle
The female moth deposits eggs silks on developing ears and sometimes on the leaves. There may be more than one egg deposited on an individual plant; however, the larvae are cannibalistic. Therefore, it is common to only find one larva on an ear.
Midwestern Corn
Generally, most corn earworm moths migrate to the Midwest from southern states in early summer. Two full generations per year are common in the Central and Northern Corn Belt. The second generation usually coincides with the reproductive stages of corn. In the Southern Corn Belt, overwintering moths usually emerge in late April and migrating adults begin to arrive in June. There are three full generations in the Southern Corn Belt, with both the second and third generations occurring during the reproductive stages of corn.
South
The corn earworm is the most common lepidopteran corn pest in the southern United States.4 There can be seven generations in South Texas and four in North Carolina. Generally, the first and second generation larvae attack whorl-stage corn in the Mid-South and later generations are found in the ear, usually the tip.1 A multi-state study conducted in the Cotton Belt indicated that corn was the major host plant during July, but other hosts became favorable in August.3 In mid to late September, corn was again the favorite plant.3
Plant Injury and Scouting
With the first generation usually coinciding with the vegetative corn stages of growth, the larvae feed in the whorl and as the leaf emerges, the leaves are ragged-edged holes that expand in size as the leaf expands. Frass or insect waste can be found on the leaves. Second and later generation moths lay eggs on the silks where they hatch, and the larvae begin clipping silks and attacking each other. Late instar larva can be easily found on the ear tip. Yield loss attributed to direct ear tip feeding is generally not economic. However, the feeding might provide an avenue for dangerous pathogens such Aspergillus flavus that is poisonous to humans and livestock.4
Management
The use of foliar insecticide applications to control CEW in corn is often impractical and rarely results in a yield benefit.4 Products containing the Vip3Aa20 protein, such as Trecepta® corn, provide excellent control of corn earworm larvae.
For additional corn earworm information and descriptions of similar pests, please see Channel® Advice, Corn Earworm in Corn.
Sources
1 Reisig, D. 2015. Corn earworm. Entomology-Insect Biology and Management. North Carolina State University Extension. https://entomology.ces.ncsu.edu/field-corn-insect-corn-earworm/.
2 Trecepta® Technology. Bayer Crop Science. https://traits.bayer.com/corn/Pages/Trecepta.aspx.
3 Reay-Jones, F. 2019. Pest status and management of corn earworm (Lepidoptera: Noctuidae) in field corn in the United States. Journal of Integrated Pest Management. 10(1):1-9. https://academic.oup.com/jipm/article/10/1/19/5512991.
4 Boyd, M.L. and Bailey, W.C. 2001. Corn earworm in Missouri. University of Missouri Extension. https://extension2.missouri.edu/g7110.
Web sources verified 6/27/22.