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Corn Rootworms Emerging (8/03/17)

Corn rootworm adults were reported emerging the last two weeks in southeastern and south central North Dakota.

Corn Rootworms Emerging

 Corn rootworm adults were reported emerging the last two weeks in southeastern and south central North Dakota. The northern corn rootworm usually emerges first; the western corn rootworm emerges one to two weeks later. Adult emergence typically is completed by mid-October.   

The potential for economic corn rootworm larval damage for the following year can be estimated by counting the number of rootworm adults on corn plants. Start scouting three weeks after pollination and continue once per week until silks are dry and brown.

Randomly select 10 nonconsecutive plants in 10 representative locations throughout the field for a total of 100 plants. During corn ear inspection, carefully cover the silk with one of your hands, then count the number of adults present by slowly allowing your hand to open. Gently disturb silks near the ear tip to dislodge and force beetles to exit.

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Also check the stalk, upper and lower leaves, leaf axils and tassel for corn rootworm beetles. Pull leaves down when inspecting the leaf axils because adults often hide in leaf axils. Count and record the number of adults of each species, then estimate the average number of adults per plant by species.

  • Threshold for first-year corn: Management in the following year’s corn crop is recommended if you find an average of two or more adults per plant for northern corn rootworm or one adult per plant for western corn rootworm.
  • Threshold for continuous corn: Management in the following year’s corn is recommended if you find an average of three or more adults per plant for northern corn rootworm or 1.5 adults per plant for western corn rootworm.

Please see the NDSU Extension Service publication “Integrated Pest Management of Corn Rootworms in North Dakota” E1852 for more information.

 

Veronica Calles-Torrez                                           Janet J. Knodel                                          Mark Boetel

Graduate Student                                                    Extension Entomologist                         Research & Extension Entomologist

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