April- June 2002
Paul Kassel , crops field specialist
The northern corn rootworm caused extensive damage to corn in northwest Iowa in 2001. Many cornfields had severe root lodging due to rootworm damage to their root systems. Wet, cool conditions in the spring, followed by warm dry conditions in the summer further complicated the root lodging conditions. Some corn hybrids appeared to be very susceptible to the rootworm damage, which added another level of complication to the problem.
Extension service personnel made farm visits to confirm the presence of rootworm damage to corn root systems. Farm visits ruled out other sources of root damage that may have caused root lodging.
Corn rootworm research on extended diapause was reviewed. Life cycle changes and rootworm biology information was reviewed. Research on the effectiveness of different corn rootworm insecticides was updated. The node-injury system of root rating was reviewed.
Information on extended diapause of the northern corn rootworm was presented at the following meetings:
A lot of farmers are going to use insecticide this year on corn that is rotated with soybeans. Seed companies and ag chemical companies have combined to offer some attractive programs for rootworm control. Typical insecticide costs are about $14 to $16.00 per acre, but some programs have reduced that cost to the farmer to about $6.00 to $8.00 per acre.
Iowa State University (ISU) research from 1987 to 1993 shows a 20% chance of a profitable yield response to insecticide use in fields with a history of extended diapause problems. Farmers who are willing to accept this risk have been reassured by this ISU information. These farmers will save about $6.00 to $16.00 per acre on their corn fields.
ISU will need to do additional research and demonstration work to continue to be a credible source of information on northern corn rootworm extended diapause.
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July 11, 2006
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