Don't forget about corn rootworms

By Tom J. Bechman
The University of Illinois documented rootworm control failure to a specific rootworm GMO trait in 2013. It’s the same trait that has been under watch in Iowa and Minnesota. However, as far as anyone knows, it hasn’t shown up inside Indiana’s borders.
This month’s panel of Indiana Certified Crop Advisers discuss if you should adjust your rootworm control strategy.
Question: I’m getting nervous because rootworm failure in Bt corn seems to be getting closer. Should I use a soil insecticide and Bt rootworm corn?
Jeff Nagel, agronomist, Ceres Solutions, Lafayette: Fields in Illinois that suffered severe damage in rotation were planted with a traited hybrid that exhibited a single corn rootworm protein, Cry3Bb1. Larval damage and beetle populations were very high. Overall rootworm populations here have trended lower in recent years, including in western Indiana which is historically a high rootworm area. All traited hybrids have still been performing well.
Dave Taylor, agronomist, Harvest Land Co-op, eastern Indiana; Seed companies are taking rootworm resistance very seriously, trying to get out in front of it across the Corn Belt. Many are recommending using a soil insecticide along with traited corn. Some recommending rotating hybrids that exhibit different rootworm control proteins. Others promote traits that exhibit multiple rootworm controlling proteins. Refuge- in-a -Bag addresses not using the proper refuge strategy.
Darrell Shemwell, agronomist, Posey County Co-op: The best way to manage corn rootworm is by rotating to soybeans, unless you have the Western Corn Rootworm variant that lays eggs in soybeans. Another option is to select a hybrid with a different mode of action, or with multiple modes of action, such as a Genuity Smart Stax hybrid.

Specific strategies

Shemwell: Several soil applied insecticides are very effective. If I were going to use a soil insecticide, I would not plant a Bt rootworm hybrid. The soil insecticide should be enough.
Nagel: I would rely on five management guidelines. First, use crop rotation when possible. Second, control volunteer corn in soybeans if the previous crop contained a rootworm GMO trait. Third, always plant the required refuge if you’re not using a refuge in the bag system.
Fourth, Where rootworm pressure has been historically higher, plant hybrids that contain two Bt proteins that are effective for rootworm control, particularly if you plant corn after corn. Fifth, consider a soil insecticide. I would reserve it for continuous corn when planting a hybrid that only has a single BT rootworm control event.
Taylor: If you’re in a high rootworm population area and are using a hybrid with a single rootworm trait, a soil insecticide is recommended. If you’re using a multiple protein for rootworm control, the insecticide is optional. If you’re in an areas where rootworm populations are lower, a soil insecticide will normally not be needed, unless it’s corn after corn.

Key points

  • If you opt for a soil insecticide, know why you’re using it
  • There are still some areas in Indiana where rotation to soybeans controls rootworms
  • In high risk areas consider use hybrids with multiple proteins for rootworm control