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Scouting for corn rootworm

Scouting beetles
Scouting beetles reveals building populations before performance issues occur, and identifies where to change management strategies to avoid this situation. Photo: Dave Baird

With the introduction rootworm-resistant Bt corn (Bt-RW corn), growers could simplify management by focusing on corn hybrids and insecticides, rather than field-by-field corn rootworm scouting. Because the Bt-RW trait was initially so effective, growers could ignore corn rootworms and drop scouting.

However, when western corn rootworm developed resistance to Bt-RW corn, it changed the game. Bt resistance added risk and the need to bring management skills back into corn production. Unfortunately, many crop producers don’t know their fields’ corn rootworm status, if they have Bt resistance and what management they’d need.

On this webpage, we’ll describe the factors affecting corn rootworm populations, two methods for scouting for them and how to decipher what these counts mean for your fields.

Why scout

By scouting for corn rootworm, crop producers can strategically reduce input costs while avoiding unacceptable rootworm risk.

Scouting rootworms provides critical information on population status, prospective injury threat and Bt resistance. Plus, it generates much-needed information for management decisions, answering critical questions such as:

  • Do I need to manage corn rootworm?

  • Do I need Bt traits?

  • Is Bt resistance developing?

  • Should I switch traits? Add a soil insecticide? Control adult beetles? Rotate crops?

Five reasons to scout

  1. Corn rootworm populations vary greatly from field to field.
  2. Heavy corn rootworm pressure can challenge performance of all management tactics.
  3. Scouting tailors management inputs to corn rootworm risk, eliminates unnecessary inputs and removes uncertainties.
  4. Scouting slows the development of resistance to Bt-RW traits and soil insecticides, when crop producers use these inputs as needed.
  5. Crop producers can detect beetle immigration into late-silking fields, and adapt management practices to the increased threat.

Understanding corn rootworm

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Whole plant count scouting technique

scouting technique
scouting technique
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Yellow sticky trap scouting technique

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Ken Ostlie, Extension entomologist and Trisha Leaf, research scientist, Minnesota Department of Agriculture

Acknowledgements

This publication is based on research funded by the farm families of Minnesota through their corn checkoff and a Monsanto Corn Rootworm Knowledge Grant. Thank you!

Reviewed in 2018

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