Corn Rootworm Protection: 4 Considerations For 2012

University of Illinois Extension entomologist Mike Gray says severe root damage has been confirmed in Bt corn in northwestern Illinois which follows a similar discovery in Iowa. Here is an excerpt from his observations:

“On August 16, I traveled to Henry and Whiteside counties in northwestern Illinois, responding to a request to verify severe corn rootworm pruning on some Bt hybrids that express the Cry3Bb1 protein. The fields have been in continuous corn production for many years, and the producers have relied on Bt hybrids that express the Cry3Bb1 protein as their primary protection against western corn rootworm injury. Lodged plants were common in many areas of the fields, and western corn rootworm adults were numerous and easy to collect. It was also easy to find plants with two to three nodes of roots completely destroyed. A shovel was not required for removing the plants from the soil.

Unfortunately, yield losses will be significant in these fields…In issue 18 of the Bulletin (August 5), I reported that field-evolved resistance by western corn rootworm to the Cry3Bb1 protein has been confirmed by Dr. Aaron Gassmann of Iowa State University. He collected resistant western corn rootworm adults from continuous cornfields in northeastern Iowa where significant root damage had occurred in producers’ fields. The Iowa fields had been planted with Bt hybrids expressing the Cry3Bb1 protein. The situations in Iowa and Illinois share some common features. Adults were collected from the Illinois fields in question and will be further evaluated for potential resistance.”

In light of the developments in Iowa and northwestern Illinois, Gray urges great caution in choosing hybrids offering corn rootworm protection when making seed selections for 2012. He says growers and retailers who have encountered less-than-satisfactory root protection this season with their Bt hybrid, consider the following alternatives for 2011:

  1. Rotation to soybeans or another nonhost crop.
  2. A corn rootworm soil insecticide at planting.
  3. A Bt hybrid expressing a different corn rootworm Cry protein than one that may have performed poorly in your fields in 2011.
  4. A pyramided Bt hybrid that expresses multiple Cry proteins targeted against corn rootworms.

“Most important, though, for effective corn rootworm management is to consider a long-term, integrated approach that includes multiple tactics, such as adult suppression programs, use of soil insecticides at planting, rotation of Bt hybrids that express different Cry proteins, and rotation to nonhost crops,” Gray said. “Many producers have relied on a single tactic for too many years, and unfortunate consequences are beginning to emerge.”

(Source: The Bulletin, University of Illinois Extension)

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