By Mike Gray, Professor and Extension Entomologist
On June 8, I received a report from Stephanie Porter, Burrus Sales Agronomist, concerning a severe infestation of armyworms in McHenry County. Significant damage had been inflicted to a field of no-till corn in which rye had been used as a cover crop. Throughout my career, the most common reports of damaging infestations of armyworms have occurred in corn when rye has been used as a cover crop. For more information on the biology, life cycle and management of this pest, please refer to the Department of Crop Sciences fact sheet regarding this insect.
No-till corn planted into a rye cover crop, McHenry County, Illinois, June 8, 2015 (Courtesy of Stephanie Porter, Burrus Sales Agronomist).
Armyworm defoliation in no-till cornfield following a rye cover crop, McHenry County, Illinois, June 8, 2015 (Courtesy of Stephanie Porter, Burrus Sales Agronomist).
Armyworms in no-till cornfield following a rye cover crop, McHenry County, Illinois, June 8, 2015 (Courtesy of Stephanie Porter, Burrus Sales Agronomist).
According to the Entomological Society of America (ESA) Handbook of Corn Insects page 50 —
“Armyworm larvae may feed only on leaf margins, or they may strip the plants, leaving only the stalks and leaf midribs. A corn plant recovers from this injury when feeding activity is moderate, as long as the growing point of the plant has not been injured. However, entire cornfields can be defoliated when an armyworm infestation is heavy and feeding damage is severe.”