University of Illinois

No. 10/May 30, 1997

Update on Heat Units for Stalk Borer Development

For those of you tracking stalk borer development and planning to manage these pests in areas where they are problematic almost every year, Figure 4 shows actual heat-unit accumulations (base 41F) from January 1 to May 26, 1997.

Figure 4. Actual heat-unit accumulation (base 41F) from January 1 to May 26, 1997, for estimating the development of stalk borers.

Remember the following:

  • Overwintering eggs hatch when approximately 575 to 750 heat units have accumulated since January 1.
  • Larvae first begin to move into corn when about 1,100 heat units have accumulated since January 1.
  • 50% movement occurs when about 1,400 to 1,700 degree days have accumulated.
  • Begin scouting when about 1,300 to 1,400 degree days have accumulated.

Also remember that very small stalk borer larvae could be causing damage to small corn seedlings now in fields that were infested with weedy host plants last fall. The presence of these larvae cannot be predicted based on the accumulated heat units associated with larval movement. You can find details about biology, identification, and management in issue No. 8 (May 16, 1997) of this Bulletin.

Kevin Steffey, Extension Entomology, (217)333-6652