One of the most potentially damaging problems facing sweet corn producers is controlling insects that feed on the ear. During the summer months, if you grow sweet corn, you need to watch for corn earworm.
Earworms are moderately hairy larvae that vary in color from yellow to green to red to brownishblack, but they all have a brown head without markings and numerous microscopic spines covering their body. You may find them feeding in the ear tips following silking. The larvae are cannibalistic, rarely is there more than one per
ear or whorl.
Corn earworm is potentially the greatest threat to sweet corn production in our state. Because it feeds directly on the ear, is difficult to control and is common in high numbers at the end of the season, most insecticides used on sweet corn target this pest. Once earworm becomes established within the ear, controlling it is impossible. Earworms spend a relatively short period of their life feeding in a site that can receive an adequate insecticide application. An effective program, especially for corn planted later in the season, is necessary to ensure a minimal amount of damaged ears.
Currently, the primary insecticides used for corn earworm control in sweet corn belong to the pyrethroid class. There is concern that corn earworm in some regions of the Midwest has developed resistance to this class of insecticides. Some field failures have been reported.
You can start a preventive program against corn earworms when 10 percent of the ears are silked. Repeat sprays at three-to-five-day intervals until 90 percent of the silks have wilted. This strategy should give a high percentage of worm-free ears during early and midseason. Control is more difficult late in the season. Even shortening spray intervals may produce only 90 percent clean ears.
For more information on sweet corn pest control, contact your local Cooperative Extension Service or check out the University of Kentucky Department of Entomology website about corn earworm control at http://entomology.ca.uky.edu/ef318.
Submitted by Ric Bessin , Extension Entomology Specialist, University of Kentucky, Department of Entomology