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Issue No. 8, Article 3/May 19, 2006

Corn Rootworm Hatch: A Memorial Day Event in Many Years

As we progress through May, interest in the annual hatch of corn rootworm larvae increases. A quick review of the last 10 years reveals that hatch very often coincides with the Memorial Day weekend celebration:

  • 2005--May 31
  • 2004--May 28-29
  • 2003--May 29
  • 2002--May 31
  • 2001--May 16
  • 2000--May 22
  • 1999--June 1
  • 1998--late May (no precise date reported)
  • 1997--June 13
  • 1996--June 12

These dates were arrived at by reviewing articles in the Bulletin and are largely based on observations by Larry Bledsoe, an entomologist at Purdue University. Larry spends time each spring looking for first-instar larvae that have tunneled into corn roots. Most of his root samples are collected from central Indiana. Although corn rootworm hatch occurs very often in late May, there have been exceptions. In 2001, hatch was very early (mid-May). In 1996 and 1997, hatch was delayed until mid-June. So we have a potential one-month range in which larval hatch may occur.

What do the soil heat-unit accumulations suggest this spring? From January 1 to May 16, 223 soil heat units (base 52°F, 4 inches) had accumulated in Champaign. During the past 11 years, an average of 279 heat units had accumulated by May 16. So we are slightly behind this average, which is not surprising in light of the very cool and wet conditions that have dominated our weather pattern for the last several weeks. We typically expect about 50% of corn rootworm larval hatch to have occurred when 684 to 767 soil heat units (base 52°F, 4 inches) have accumulated. Unless we see a return of much warmer weather over the next few weeks, we may observe a later (early June) corn rootworm larval hatch than we've experienced in recent years. For more information about current and projected heat-unit accumulations for a variety of insect pests, take a look at the Degree-Day web site.

Corn Rootworm eggs on a penny.

Please pass along any confirmations of the corn rootworm larval hatch when it occurs in your area of the state.--Mike Gray

Mike Gray

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