Insecticide Resistance Management (IRM)

Insecticide resistance management practices include implementing a plan that reduces the chances of insects becoming resistant to the insecticide. When transgenic crops, such as corn containing Bt, are planted the intent is to prevent insects from causing yield-reducing damage. However, if a farmer always plants all acres to Bt corn, insects within this area are only exposed to corn containing Bacillus thuringiensis. This can become a problem if the insects become resistant to this type of “all Bt” environment resulting in significant damage.

In order to prevent insecticide resistance from happening, a management plan should be put into place. Current IRM requirements call for planting a portion of the farmable acreage to non-Bt corn. Having this percentage (20%) of all planted acres in non-Bt corn may prevent insecticide resistance. The acres planted to non-Bt corn are referred to as the field refuge. There are five different refuge designs, 1) Linear Block, 2) Bracket, 3) Border or Perimeter, 4) Block, and 5) Strip. Click on the following animation or go to the interactive Refuge Designs animation to see the five designs.

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The EPA (Environmental Protection Agency) has created a list of IRM requirements. These requirements help to maintain an insecticide resistance management plan, which will prevent resistance to Bt crops. IRM requirements help maintain the integrity of transgenic Bt crops. The following list outlines these requirements (Pilcher, 2003; Wright and Hunt, 2004).

  1. Plant no more than 80% of corn acres to YieldGard Rootworm corn
  2. Refuge needs to be a minimum of 20% of corn acres
  3. Refuge must be adjacent to or within YieldGard Rootworm corn field
  4. Refuge options include: YieldGard Corn Borer, Roundup Ready® corn, or a conventional hybrid
  5. Refuge may be treated for CRW with soil-, seed-, or foliar-applied insecticides
  6. If a strip design refuge is used, the strips should be no fewer than six rows
  7. YieldGard Rootworm corn and refuge must be in the same rotation and managed by the same grower
  8. If refuge is treated for other late-season insect pests such as corn borer, then YieldGard Rootworm field must also be treated