New Bt stacks require review of IRM guidelines

Growers considering new corn hybrids with stacked Bt technologies should take a close look at insect-resistance management (IRM) requirements for 2005. Regulations accompanying these products, such as newly available Pioneer brand hybrids with the YieldGard1 Plus trait, incorporate compounded guidelines in the United States.

For example, the YieldGard Plus technology is a stack containing both the YieldGard1 Corn Borer gene and the YieldGard1 Rootworm gene. The refuge acreage requirements differ for these two technologies.

“Pioneer brand hybrids with the YieldGard Plus trait have two separate insect-protection genes,” Alex Woodall, product stewardship manager for Pioneer Hi-Bred International, Inc. “Managing two genes can be complex in regard to refuge acreage and location requirements, but it's essential to preserving their effectiveness now and in the future.”

Growers can meet IRM requirements through common or separate refuges. In a common refuge, the YieldGard Corn Borer and YieldGard Rootworm traits in YieldGard Plus hybrids are managed as one component. The refuge must be within or adjacent to fields containing the YieldGard Plus traits.

Separate refuges are designed to work independently for each Bt trait. The corn borer and rootworm components of hybrids with the YieldGard Plus traits are managed separately for refuge purposes to allow flexible refuge design. The corn rootworm refuge must be within or adjacent to the YieldGard Plus field. However, the corn borer refuge can be up to a half mile from the YieldGard Plus field.

A more complex issue is the various refuge percentages in non-cotton growing areas versus cotton growing areas.

In non-cotton growing areas, up to 80 percent of corn acres in each field can be planted with hybrids that contain Bt corn borer protection or rootworm protection. A minimum of 20 percent of corn acres must be planted with hybrids that do not contain a Bt gene for corn borer protection or rootworm protection.

In cotton growing regions, hybrids with the corn rootworm trait require only a 20 percent refuge. However, hybrids with a corn borer trait require a 50 percent refuge. Thus, using a separate refuge configuration for YieldGard Plus in these areas allows a grower to plant up to 50 percent of a field to hybrids with YieldGard Plus. They can plant another 30 percent of the same field to hybrids containing YieldGard Rootworm technology. At least 20 percent of the field must contain a refuge without either technology.

Although the new regulations may be complex, Pioneer will assist customers to help them be good stewards of available technologies.

“Working with customers to insure the highest possible level of compliance with IRM requirements is a Pioneer mission,” Woodall said.

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