IRM Calculator Helps Growers Plant the Right Refuge for the Right Bt Corn Hybrid

IRM Calculator Helps Growers Plant the Right Refuge for the Right Bt Corn Hybrid

Eileen Cullen, Extension Entomologist

In 2011, more corn hybrids contain multiple Bt traits for insect control or suppression. Refuge requirements have changed for multi-trait corn hybrids with pyramided traits (two or more Bt traits for the same insect pest complex above and/or below ground) and seed blend refuge-in-the-bag products.  Some product refuges remain at 20% and ‘structured’ in blocks in or near the field, or rows within the field. Others are reduced to 5% structured refuge, while others are ‘in the bag’ at a 10% refuge seed blend for corn rootworm mixed in with the Bt seed.

The National Corn Growers Association has an excellent user-friendly IRM Refuge Calculator available for free download and use on your computer. To download the program visit: 

From the NCGA website above: “This IRM refuge calculator is a tool intended to illustrate the appropriate refuge calculation, the quantity of standard seed bags to purchase for both trait and refuge, and illustrate possible planting configurations for planting certain corn products in the U.S.  This refuge calculator does not replace or supplement the applicable manufacturer’s IRM Grower Guide in any way. As a grower using this information, you are still obligated to understand and abide by the applicable IRM Grower Guide on planting and Insect Resistance Management.”

I have used the IRM Calculator twice this week as growers make plans for spring planting – Once on a phone call with a UW-Extension county agent and his grower calling in to my office, and yesterday while teaching Entomology 351 field and forage crops module at UW Madison entomology department.  I found the program very easy to download and use on PC.  I was not able to download the Mac version successfully and have contacted the NCGA site about this. You may have better luck with the PC download.

In six easy steps, you enter the type of Bt corn hybrid (classified on the IRM Calculator as: Corn Borer Only Traits, Corn Rootworm Only Traits, or Stacked Traits) particular seed product trade name, field size, and seeding rate.  The IRM Calculator will calculate for you how many acres of Bt trait and refuge corn you need to plant, respectively, and how many bags of each you need to plant the field. You can calculate this for a single field or a farm. At the end of the six steps you get a color graphic illustrating options for how to configure the refuge in the field.  (The program also allows an option for pivot irrigation setups).

For more information and to review current Bt corn hybrid trait choices and insect resistance management (IRM) refuge requirements please visit the following Wisconsin Crop Manager newsletter links and UW Extension entomology resources:

Keeping up with Bt Corn Insect Traits and Refuge Requirements

Wisconsin Crop Manager 17(9): 36-38.

Handy Bt Trait Table

Michigan State University and UW Extension Fact Sheet

Corn Insect Traits 2011

UW Madison Nutrient and Pest Management Fact Sheet