Looking for unexpected damage to rootworm Bt corn

A plea to report fields with unexpected damage to Bt rootworm corn.

The rest of July and early August is prime time to check and identify Bt fields with unexpected damage from corn rootworm. Continuous corn fields planted to Cry3Bb-type corn (VT Triple and Pro) are most at risk because this trait has been in use longer than other corn rootworm traits. However, unexpected damage in any type of Bt rootworm corn should be investigated. Areas in Michigan with a concentration of livestock production, thus a higher percent of corn-after-corn acres, should be a target.

If you find a field with unexpected damage or a huge number of beetles, and other causes are ruled out, please call both the seed dealer and me, Chris DiFonzo, at 517-353-5328. The seed dealer can assist in diagnosing the problem and has an obligation to report sites with suspected resistance. I can test the plants for Cry3Bb Bt and my lab is set up to raise beetles to collect eggs for resistance testing.

The important thing is to identify sites early and report them immediately so we can document the problem and collect enough beetles. The better job we do in diagnosis, the better recommendation we can provide for your farm or your clientele for 2014.

Learn more about the causes, identification, and management of Cry3Bb1 resistance:

  • Read the white paper written and signed by nine entomologists in the eastern Corn Belt.
  • Download a four-page bulletin that summarizes our recommendation for producers.
  • Listen to the NPR report from July 9, 2013, “As Biotech Seed Falters, Insecticide Use Surges in Corn Belt.”

Dr. DiFonzo's work is funded in part by MSU's AgBioResearch.

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