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Refuge in a Bag Protects Corn Traits


Refuge in a Bag Protects Corn Traits

by Bill Mahanna and Ev Thomas

Being good stewards of corn genetics that contain insect-killing proteins from the bacterium Bacillus thuringiensis (Bt) is a topic all seed companies are thinking about. When Bt hybrids entered the market, the U.S. Environmental Protection Agency (EPA) required growers to plant "refuge" acres with corn hybrids that did not produce Bt proteins. However, research tells us that this wasn't taking place on all farms.

Refuge acres with non-Bt corn ensures the survival of some susceptible insects feeding on non-Bt crops. This reduces the chance ofinsects that may evolve resistance to the Bt proteins by mating only with other resistant insects and producing resistant offspring.

Why does this matter? Large populations of resistant insects would reduce the economic value of Btcorn, that value being higher yields under insect pressure, less need to rotate acres and a significant reduction in the use of insecticides.

Simplifying refuge management benefits growers by offering convenience and ensuring the longevity of the trait is maintained in the growing environment. For seed companies, it helps guarantee compliance with the insect resistance management (IRM) requirements overseen by the EPA and supports its ability to continue to commercialize future biotechnology traits.

When Bt hybrids first entered the market in 1996, a 20 percent structured refuge was standard throughout the Corn Belt. Structured refuge means a defined portion of the field (blocked area, four-row perimeter or four-row split planter strips) has to be planted with a hybrid that does not contain Bt genes for the control of corn borer. This creates an inconvenient seeding patchwork and planter box roulette which complicates the IRM compliance assurance programs overseen by seed companies. Failure of growers to comply with signed technology agreements dictating IRM requirements could result in denying them future access to Bt corn.

In 2003, Bt hybrids for corn rootworm were released and a similar 20 percent structured refuge was implemented. The mating characteristics and dispersal patterns are much different for corn rootworms compared to European corn borers, yet a 20 percent refuge was mandated for consistency and the hope it would reinforce the 20 percent refuge required for corn borer hybrids.

Growers today have greater flexibility in meeting refuge requirements at planting. This is a result

of the seed industry commercializing integrated refuge by blending refuge seed in the same bag as the traited corn. In 2010, EPA approved the seed industry's first corn product (Optimum AcreMax 1) with corn rootworm refuge blended in the bag and reduced the refuge requirement to a 10 percent level. This advanced in refuge strategies satisfied all corn rootworm refuge requirements in one bag of seed and allowed growers to plant required corn borer refuge up to one-half a mile away.

The latest development is using pyramided Bt hybrids. This term applies to the use of Bt corn hybrids that produce a combination of Bt toxins. This is commonly referred to as separate modes of action for above-ground (corn borer) control and separate modes of action for below-ground (corn rootworm) control. For example, the EPA currently requires 20 percent of the total acreage being set aside as refuges for corn producing one Bt protein (Cry3Bb1), and a 5 percent refuge portion for corn that simultaneously produces two different Bt proteins.

Greater grower acceptance

A survey among 608 Illinois corn growers attending the January 2012 Corn and Soybean Classic meetings indicated that over 90 percent intended to plant Bt corn. About 53 percent of growers were still using the traditional 20 percent Bt refuge approach. However, as more pyramided Bt hybrids enter the marketplace, 37 percent indicated they would a use integrated refuge as a hedge against insect resistance development for this crop year. About 60 percent of producers intending to plant integrated refuge hybrids indicated they would use a 5 percent seed blend. The other 40 percent intended to plant a 10 percent seed blend. The organizers of these meetings indicated the grower response represented a significant shift away from the structured refuge. They also believe that the trend would likely intensify as more pyramided hybrids become available.

The seed industry is continuing to bring forth innovative solutions to help growers conveniently meet refuge requirements. The goal is grower simplicity, protecting high yields and technology. However, there is still a fair amount of complexity in sorting through all the insect protection products in the marketplace which differ in the amount of refuge hybrid contained in the bag and their specific use. This is especially true for refuge requirements in Southern cotton growing areas which are much more stringent. As recommended in previous columns, the single best person to help guide dairy producers through the growing product offerings is your seed sales professional.


Used by permission from the November 2012 issue of Hoard's Dairyman.
Copyright 2012 by W.D. Hoard & Sons Company, Fort Atkinson, Wisconsin.