Issue No. 14, Article 7/June 24, 2005
European Corn Borer Larvae Found in Whorls
Keep an eye out for first-generation European corn borer larvae. Scouts in several areas have found European corn borer larvae feeding in corn whorls. Fall surveys of second-generation European corn borer larvae revealed record statewide lows of corn borer densities. We've yet to determine how the first generation has fared this spring.
Scouting for first-generation corn borers should begin when corn plants have reached an extended leaf height of 18 inches. First-generation larvae are found feeding on the leaves of corn in mid- to late-whorl stages. They chew small holes in the leaves, creating a "buckshot" effect. As corn borers mature, they leave the whorl and begin tunneling in leaf midribs and sheaths. After reaching approximately 1/2 inch in length (third instar), borers tunnel into the stalk and feed until fully grown.
Whorl-feeding injury caused by first-generation European corn borer larvae (University of Illinois).
First-generation European corn borer larvae (University of Illinois).
If possible, 25 consecutive plants should be examined in each of five random locations for every 80 acres within a field. Walk at least 100 feet into a field before checking plants for corn borer larvae. If more than one corn variety is being grown or if differing planting dates occurred in the same field, it is important to consider each section as a separate field. Plants should be checked for fresh whorl feeding, and the percentage of infested plants calculated. For every 20 to 25 plants examined, pull the whorls of two plants and check for live borers. This will allow you to estimate the average number of borers per infested plant. After scouting the field, you can use the First-Generation Management Worksheet (http://www.ipm.uiuc.edu/decision/corn_borer_first.html) to make the appropriate management decision.
For more information on European corn borer, please visit the fact sheet on the IPM Web site (Adobe PDF), and stay tuned for more information on European corn borers.--Kelly Cook