Corn Earworm on Corn

The corn earworm is the most common pest of corn in South Carolina. It can be found in virtually every field, and probably as high as 90% of all ears may show signs of feeding.

When plants are small, eggs are laid on the leaves. Early season worms move down into the whorl of the plant and feed on the foliage. At this stage the worms cover themselves with a plug of frass that generally protects them from predators, parasites, and insecticides. However, application of a recommended insecticide in a coarse spray may give adequate control of whorl-feeding insects. Proper timing is essential. Although the corn may take on a ragged appearance, the plant can usually grow out of this early season foliage damage. However, late-planted corn may suffer much more severe damage.

As the season progresses, the moths lay their eggs on fresh corn silk. Several eggs may be laid on a single silk. However, generally only one will mature as a result of predators, parasites, or cannibalism. The larvae then feed upon the ear, though damage is usually limited to the tip of the ear. An important factor in this later damage is that the earworm injury may expose the ear to diseases or other insects that otherwise could not gain entry into the ear.

Chemical control of the corn earworm, as well as other whorl-feeding caterpillars, may be accomplished through the use of any one of several insecticides. However, control is usually  not economically feasible unless there is danger of losing more than 10% of the buds before tasseling. These products should be applied as a coarse spray in at least 15 gallons of total spray per acre, or as granules. Either formulation should be applied directly into the whorl of the plant. Since the list of labeled products is constantly changing, and since available products varies from state to state, there will be no mention of specific products. With all insecticides, read and follow label instructions carefully.

Prepared by Donald G. Manley, Extension Entomologist/Professor, Department of Entomology, Soils, and Plant Sciences, Clemson University.

This information is supplied with the understanding that no discrimination is intended and no endorsement by the Clemson University Cooperative Extension Service is implied. Brand names of pesticides are given as a convenience and are neither an endorsement nor guarantee of the product nor a suggestion that similar products are not effective. Use pesticides only according to the directions on the label. Follow all directions, precautions and restrictions that are listed.

The Clemson University Cooperative Extension Service offers its programs to people of all ages, regardless of race, color, sex, religion, national origin, disability, political beliefs, sexual orientation, marital or family status and is an equal opportunity employer. Clemson University Cooperating with U.S. Department of Agriculture and South Carolina Counties. Issued in Furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of May 8 and June 30, 1914.