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Issue No. 7, Article 1/May 18, 2012

Corn Rootworm Larval Hatch: Earliest in at Least 35 Years

Long-time Purdue University entomologist Larry Bledsoe has reported observing corn rootworm larvae (1st instars) on May 8 in Tippecanoe County, Indiana, north and west of Indianapolis. He says this is the earliest he has found corn rootworm larvae in 35 years! His estimate is that hatch occurred between May 4 and May 6.

Before this observation, May 16 (2001) was the earliest early-season larval hatch in the past 17 years. Generally, the initial hatch occurs near the end of May and into early June. In fact, in the past four years, Larry’s first reports of larvae were in early June.

A review of Bulletin articles since 1996 reveals the following estimates of hatch (for central Illinois and Indiana), based on Purdue University observations provided by Larry Bledsoe.

  • 1996--June 12
  • 1997--June 13
  • 1998--late May (no precise date reported)
  • 1999--June 1
  • 2000--May 22
  • 2001--May 16
  • 2002--May 31
  • 2003--May 29
  • 2004--May 28
  • 2005--May 31
  • 2006--May 29
  • 2007--May 18
  • 2008--June 4
  • 2009--June 1
  • 2010--June 3 (second instars observed)
  • 2011--June 6
  • 2012--May 4–6

What are the potential implications for corn producers this season? By May 7, 89% percent of corn acres were planted across Illinois, as reported by the USDA NASS Illinois field office in Springfield. Unlike in previous recent years, corn rootworm larvae this spring will be feeding on small-rooted corn plants in drier soil conditions. We have had wet springs in recent years, and corn rootworm larvae struggled to survive in saturated soils at the time of hatch.

This will not be the case in many fields this spring. As of May 7, moisture conditions in topsoil across the state were 6% short, 68% adequate, and 26% surplus (USDA, NASS, Springfield). I anticipate good larval establishment this season, and where densities are high, significant pressure will be exerted on the root systems of corn plants throughout May and into mid-June. With a larval hatch some 3 to 4 weeks early, anticipate the early arrival of adults this year as well, possibly by mid-June.

If you encounter significant rootworm injury on Bt plants this spring, please let me know. I would like to share these observations with readers. Thanks.--Mike Gray

Author:
Mike Gray

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