Large Black Cutworms vs. Emerging Corn Plants

Published: May 3, 2011

Late planting of many corn fields in the state raises the potential for damage from black cutworm larvae in some regions of Missouri. Moth data and intensive moth capture data reported through the Missouri IPM pest monitoring network is available at http://ppp.missouri.edu/pestmonitoring/bcw/index.cfm.

Listed below are the trap locations with intensive captures (as of 5/3/11) and predicted dates of first cutting of field corn by black cutworm larvae:

Northwest Region
Holt County (Forbes):

• Intensive capture date, 04/06/2011
  Predicted first cutting, 05/09/2011
• Intensive capture date, 04/18/2011
  Predicted first cutting, 05/18/2011

• Intensive capture date, 04/06/2011
  Predicted first cutting 05/09/2011
• Intensive capture date, 04/18/2011
  Predicted first cutting 05/18/2011

West Central Region
Vernon County (Nevada):

• Intensive capture date, 03/27/2011
  Predicted first cutting, 04/29/2007
• Intensive capture date, 04/01/2011
  Predicted first cutting, 04/29/2011
• Intensive capture date, 04/06/2011
  Predicted first cutting, 05/03/2011
• Intensive capture date, 04/22/2011
  Predicted first cutting, 05/17/2011

Central
Callaway County (Hatton):

• Intensive capture date, 04/08/2011
  Predicted first cutting, 05/06/2011

• Intensive capture date, 04/25/2011
  Predicted first cutting, 05/19/2011

• Intensive capture date, 04/25/2011
  Predicted first cutting, 05/19/2011

North East Region
Knox County (Novelty):

• Intensive capture date, 04/11/2011
  Predicted first cutting, 5/16/2011
• Intensive capture date, 04/14/2011
  Predicted first cutting 5/19/2011
• Intensive capture date, 04/18/2011
  Predicted first cutting 05/20/2011
• Intensive capture date, 04/25/2011
  Predicted first cutting, 05/22/2011
• Intensive capture date, 04/28/2011
  Predicted first cutting, 05/22/2011
• Intensive capture date, 04/29/2011
  Predicted first cutting, 05/23/2011
• Intensive capture date, 05/03/2011
  Predicted first cutting, 5/25/2011

East Central Region
Franklin County (Union):

• Intensive capture date, 04/05/2011
  Predicted first cutting, 04/29/2011

The potential for black cutworm damage increases in late planted corn. The preceding data indicate that although some cutting may now be occurring, the potential for heavy cutting exists for the latter half of May. Considering current field conditions where wet soils have delayed corn planting in much of the state, it is likely that situations will develop where seedling corn plants will be exposed to relatively large black cutworm larvae in those areas where intensive captures of black cutworm moths have been reported. Corn plants are susceptible to black cutworm damage up to the 5-leaf stage of plant growth. Be sure to scout all corn fields for the presence of black cutworm larvae on a weekly basis until this plant growth stage is reached, but especially those fields that are late planted. As previously published in the newsletter, the traditional economic threshold for black cutworm cutting in field corn is 4-6% cutting above ground and 2-3% cutting below ground. These thresholds are valid for Missouri although as the price of corn increases it becomes economically possible to protect the yield at a lower percent cutting than when corn prices are low. A couple of years ago entomologist at Iowa State developed a pest model for black cutworm which indicated that as the corn price exceeds $5-$6 per bushel, the economic threshold may be lowered to 2% for both above and below ground types of cutting. Bases on a review of the Iowa State calculations, Missouri pest management recommendations for cutting of seedling corn plants by black cutworm larvae were modified in 2011 to follow the economic threshold of 2% or more seedling cutting of either type. If the price of corn comes down in the future, then the percent cutting threshold may need to be increased back to the traditional economic thresholds used for this pest in the past. Remember that most feeding damage to corn by black cutworm larvae will typically occur within 7-10 days following plant emergence.