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Adult Corn Rootworm Emerging (07/30/20)

The first emergence of adult northern corn rootworm are being observed in corn fields near Sheldon, Ransom County and Barney, Richland County.

The first emergence of adult northern corn rootworm are being observed in corn fields near Sheldon, Ransom County and Barney, Richland County. Other counties scouted that had no corn rootworms are Barnes, Cass and Sargent. Adult corn rootworm beetles can easily be identified in the field. Northern corn rootworm adults are tan to pale green, 1/4 inch long beetles (see picture).

No western corn rootworms were observed yet. Western corn rootworm adults emerge one to two weeks later than northern corn rootworms in North Dakota. They are from 3/16 to 5/16 inch long and yellowish-green with three black longitudinal stripes on the female’s forewings and nearly solid black marking on the male’s forewings.

Begin field monitoring for corn rootworm adults a few days before the silking stage. Monitor corn plants by walking down corn rows and searching for adult beetles on the corn ear. Adults are most active during midmorning or late afternoon, so scouting within these time periods is preferable. If no adults are found, then no further scouting is needed for three days. Continue to scout the field twice per week until pollination ends. If rootworm beetles are detected in the field, randomly select five nonconsecutive plants in 10 different locations throughout the field. Count and record the number of rootworm adults while keeping track of the number of plants sampled, and then calculate the average number of beetles per plant. Weekly scouting maps are posted weekly on the NDSU Extension IPM website. For more information on corn rootworms, please see the NDSU Extension publication Integrated Pest Management of Corn Rootworms in North Dakota E1852.

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Janet J. Knodel

Extension Entomologist

 

Veronica Calles-Torrez

Post-doctoral Scientist

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