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What to do if you experience unexpected damage to corn rootworm resistant corn

Ken Ostlie, University of Minnesota

The development of either western or northern corn rootworm resistance to transgenic Bt-RW corn is a major concern. Resistance to Monsanto's trait by western corn rootworm has been detected in the Midwest but all single traits and their pyramids are “at-risk” for resistance. If you note unexpected levels of corn rootworm injury or lodging, or suspect performance problems with any Bt-RW hybrid, please take the following steps:

  • Consult your planting notes to determine the hybrids in the field and your placement of Bt-RW and refuge corn.
  • Verify where problems are occurring in the field. Look at lodging. Dig a few roots to verify corn rootworm damage. Note the corn rootworm species in the field and, if present, their abundance. Are there signs of corn rootworm activity (silk clipping, leaf feeding)?
  • After initial verification of the problem, contact your seed dealer to report unexpected corn rootworm injury. Arrange to have an independent ag professional familiar with corn rootworm present for the field visit(s) by the company. The dealer may also bring additional expertise to the field visit. Each company has its own internal reporting process … but expect these elements:
    • Verification of seed purchase.
    • Ground truth of planting information, including both Bt-RW and refuge corn, by testing of corn leaf / root tissue with gene check kits to verify their placement in the field and ensure Bt-RW expression.
    • Digging roots at representative locations throughout the Bt-RW field and the associated refuge to determine whether or not excessive corn rootworm feeding has taken place. Make sure to check both lodged and standing corn in representative areas of the field.
    • A quick examination of lodging patterns within the field and presence/abundance of corn rootworms, if reported early enough in the summer.
    • Field history information including cropping history and management practices.
  • If unexpected corn rootworm damage is verified, the company may go through additional steps to diagnose if resistance is occurring, including sampling the beetles, if present, and may request management steps for the field in the following corn crop.
  • Share information on your performance problem field with us.

Kenneth Ostlie
Professor and Extension Entomologist
University of Minnesota
Department of Entomology
1980 Folwell Ave., Rm. 219
St. Paul, MN 55108-6125
Cell: (612) 750-0993
Office: (612) 624-7436
Fax: (612) 625-5299
Email questions on corn rootworm