February 3, 2012

We conducted a survey of crop consultants attending the December 2011 Nebraska Independent Crop Consultants Association (NICCA) meeting in North Platte to get a better idea of their experience with rootworm-active trait Bt corn hybrids in 2011. The survey was a follow-up to reports we received during 2011 of unexpected damage by rootworm larvae on Bt hybrids expressing the Cry3Bb1 protein, (see Sept. 22, 2011 CW story). Twenty-eight consultants completed part or all of the survey, the results of which are reported below. All surveys were anonymous.

• Responding consultants worked in 47 Nebraska counties; each worked in an average of 4.4 counties
   
• Unexpected rootworm injury to rootworm Bt hybrids was observed.   Yes: 16     No: 12

• Unexpected damage was identified by:
  
  Root injury rating: 13
  Lodging: 16
  Yield: 8 (always coupled with the other criteria)

• Total corn acres consulted in 2011 (all corn, not just Bt hybrids)
  
  369,500 acres
   
• Estimated total Bt acres with unexpected rootworm injury
  
  10,030 acres (2.71%), all continuous corn

• Hybrid/event with unexpected rootworm damage
  
  YieldGard/Genuity (Cry3Bb1): 14
  Herculex RW or HXX (Cry34/35): 4
  Agrisure RW (mCry3A): 2
  SmartStax: 2
  Optimum AcreMax: 0

These results suggest Bt rootworm problem fields were localized in areas with continuous corn and relatively uncommon in Nebraska in 2011. Although Cry3Bb1-expressing hybrids were linked with unexpected damage more than other rootworm trait Bt hybrids, we do not have data on market share in Nebraska of the different hybrids/events. This market information would help us interpret the relative frequency of unexpected damage reported for different hybrids/events. Various factors can contribute to unexpected damage by rootworm larvae. Therefore, UNL is conducting research to assess the susceptibility of Nebraska rootworm populations to rootworm-active Bt corn traits to determine if resistance to one or more Bt traits is contributing to the unexpected damage observed in the field.

More Information

See the Sept. 22, 2011 Crop Watch article, Corn Rootworm Management Update:  Ensure Diversity When Selecting Seed for 2012, for a discussion of corn rootworm management options if you experienced unexpected rootworm damage to your Bt corn hybrids in 2011.

Bob Wright, Professor of Entomology and Extension Specialist
Lance Meinke, Professor of Entomology