Black Cutworms Are Busy Reducing Stands in Cornfields

May 28, 1999
Doug Gucker, University of Illinois Extension, Piatt County, reported on May 25 that a number of cornfields in Piatt County had black cutworm infestations with cutting in the 4 to 6 percent range. Damage in some fields was severe enough to warrant replanting. Much farther north, Jim Blackburn, Terra Industries, reported that a cornfield in northeastern Lee County had 3 percent of the plants cut, with 30 percent of the plants displaying leaf feeding. For approximately a week, John Grandin, Spoon River FS, Inc., Knoxville, has observed economic levels of cutting in cornfields located in Fulton and Knox counties. Some producers who were required to apply rescue treatments for black cutworms are beginning to question the wisdom of the rescue approach. Don't forget the following facts: (1) rescue treatments typically offer superior control to that of planting-time soil insecticide applications, (2) black cutworms are occasional pests and infestations are very sporadic, and (3) the wait-and-see approach to black cutworm management makes economic and environmental sense.

A number of producers this week indicated that because they got busy with soybean planting, they neglected to monitor cornfields and suffered some economic levels of cutting. In some instances, replanting portions of cornfields will be necessary. A question frequently asked was, "Do I need to apply an insecticide spray to the area of the field that will be field cultivated or disked before I replant?" Research conducted by Dr. William Showers, USDA-ARS, Iowa State University, and published in 1985 indicated that when tillage operations or herbicide treatments were applied 8 or 14 days prior to planting, minimal cutting of corn seedlings occurred, presumably because cutworm larvae starved. If tillage operations and herbicide treatments were delayed until 2 days prior to planting or were made the same day of planting, more corn plants were cut. The researchers believed that corn plants emerged before significant numbers of black cutworms starved. These entomologists assumed that cutworm larvae survived on plant debris (at least 10 days) until corn emergence occurred. So, although tillage prior to replanting will likely increase the level of black cutworm mortality, these insects are resilient and may still inflict cutting to newly emerging corn seedlings. If an insecticide is not used prior to replanting, these fields should be monitored very carefully and a rescue treatment applied if needed.--Mike Gray

Author: Mike Gray