Corn growers can now choose between Agrisure Bt corn hybrids for corn borer control and YieldGard or Herculex Bt corn-trait families for corn rootworm control, corn borer control or both. However, with the increased choices between Bt corn brands and products, a little more confusion may creep in when farmers seek to comply with Environmental Protection Agency (EPA) planting regulations.
“Different technologies have different requirements, which can lead to confusion,” says Lance Bailey, product stewardship manager for Pioneer Hi-Bred International, Inc. “Be sure to read the product use guide provided by the company and understand the regulations. Things change all the time. The best thing farmers can do is stay in contact with their local seed company representative to develop a refuge plan that meets regulation requirements.”
The EPA requires farmers who plant Bt corn to follow specific, insect resistance management (IRM) practices that include planting a refuge area for insects that are being targeted by Bt technology. (See “Refuge Rules Roadmap,” Jan. 2004, for an earlier discussion on this topic.) The size of the refuge area should be at least 20% of the area planted to Bt corn, except in southern corn and cotton growing areas, where the minimum refuge area is 50%.
“There are some important differences among the Bt corn products, which insects they control, and their refuge requirements,” says Bob Wright, University of Nebraska Extension entomologist. “It's probably best to check with a seed salesman for the technical literature that describes the specific refuge requirements involved.”
The most recent Bt corn products to become available to farmers are Herculex RW Bt corn hybrids for corn rootworm control and Herculex XTRA, which combines the Bt proteins in Herculex I (for corn borer control) with Herculex RW, says Wright. The two main target pests for Bt corn products are either corn borer or corn rootworm, he explains. The refuge requirements are different, depending on whether one or both pests are being targeted, he adds.
“A corn borer refuge could be up to a half-mile away from the Bt cornfield, but the rootworm refuge has to be either within the same field as the Bt corn rootworm hybrid or adjacent to it,” points out Wright. “The refuge requirements are based on the different behavioral aspects of the two different insects.”
Both Bt cornfields and their refuge areas need nearly identical management to be effective for IRM purposes, says Wright. “Some people in the western Corn Belt are tempted to plant the non-irrigated pivot corners as the refuge,” he explains. “This is not recommended, as the non-irrigated area may not grow similarly to the irrigated part of the field.”
Farmers should also learn the difference between common and separate refuge areas. A common refuge serves to address the requirements for both corn borers and corn rootworms. A separate refuge serves to address the requirement of only one primary insect, either corn borer or corn rootworm, but not both. (Note the potential configurations in the graphic below.)
For example, a separate refuge area for a Bt corn rootworm hybrid must be planted to either a conventional corn hybrid or a Bt hybrid that controls corn borer but not corn rootworm. Farmers would be breaking the EPA's IRM requirements if they planted a Herculex RW hybrid as a refuge for YieldGard RW hybrid, or vice versa, says Ken Ostlie, a University of Minnesota Extension entomologist.
“The purpose of the refuge is to dilute genes of beetles that might otherwise develop resistance,” he says. “However, refuge management plans also recognize the farmers' need to protect that field with a soil insecticide or a seed treatment.”
Most corn growers do a good job following stewardship compliance agreements for growing Bt corn hybrids, says Bailey, “We have a high level of compliance with all of our Bt technology in the marketplace.”
To help growers stay in compliance this growing season, Pioneer has developed the following refuge management tips:
Most farmers prefer to plant a refuge within the Bt field. This can be done several ways — as a block, as a perimeter or border or with a split planter. However, mixing Bt and non-Bt seed in the planter is not an approved option.
A refuge for corn borer Bt products can be planted within one-half mile (one-quarter mile is better) of each Bt cornfield. For corn rootworm Bt products, refuges must be planted within or adjacent to Bt fields. Be sure to mark each Bt field at planting to make it easier to monitor throughout the season.
Select a hybrid for the refuge that has similar agronomic traits to the Bt hybrid so the refuge will be as attractive to adult insects as the Bt field. This will also allow growers to harvest both at the same time. It's especially important to match the hybrids in maturity, early vigor and plant height.
Use the same management practices in both the Bt field and the refuge. Begin by planting both fields at the same time, and follow through with identical fertility programs, including starter and sidedress fertilizers.
Also be sure to use the same tillage practices. Variations in soil residue levels create different soil temperatures, which in turn can lead to critical differences in early insect development. Don't cut corners. It may be tempting to plant the refuge on less productive land or cut back on inputs, but both practices can reduce its effectiveness. Paying attention to small details can go a long way toward getting the best return on investment.
Common or separate refuges
In non-cotton growing areas, a common refuge must equal 20% of the corn acres planted, in the same field as or adjacent to Bt hybrids. The common refuge cannot contain Bt proteins active against rootworm or corn borer.
A separate refuge in non-cotton growing areas must contain both a 20% corn borer refuge that cannot contain a Bt protein active against corn borer and a 20% rootworm refuge that cannot contain a Bt protein active against rootworm. The corn borer refuge must be within 1/2 mile of the Bt field. The corn rootworm refuge must be in the same field or adjacent to the Bt hybrids.
Even with modern technology, there is no substitute for walking fields regularly to stay on top of what is happening. Any unexpected insect feeding damage should be reported to your seed sales representative.
For more information on Bt corn refuge rules, visit:
Bt Corn Refuge Rules: Too Much ‘Hassle?’
A 2004 Purdue University survey of about 1,000 Indiana farmers found that as corn growers approach late middle age, they are less likely to plant corn that produces Bacillus thuringiensis (Bt), a protein that kills corn rootworms and European corn borer insects that feed on plant tissues.
The survey also found that farmers who are experienced with other biotech crops are more likely to plant Bt corn hybrids, while some growers are less inclined to use Bt varieties, because they find planting parts of their fields in non-Bt “refuge” corn a “hassle.”
Older farmers who have never planted Bt hybrids aren't likely to start, says Corinne Alexander, a Purdue agricultural economist and the study's lead researcher. “Once they reach about age 48,” she says, “they become less likely to adopt the technology.”
The reasons include time and profit potential, adds Alexander. “Farmers who are very concerned about pollen drift contaminating adjacent fields were significantly less likely to adopt Bt corn,” she points out. “There's a small group that dislikes the refuge requirement and, because of that, they are not planting Bt crops. But by and large, producers said refuges were not that big a deal — just follow the rules, plant them and it doesn't take much extra time.”
Among other findings in the Purdue study:
Growers who have planted genetically modified corn to control other corn pests would plant corn rootworm Bt hybrids, if given the opportunity. “We found that producers who had planted Bt corn that controls European corn borer in 2003 were significantly more likely to plant corn rootworm corn,” says Alexander.
Europe's refusal to purchase many biotech grains — and the influence that decision has had on corn buyers within the U.S. — leaves some Indiana corn growers hesitant to plant corn rootworm-resistant hybrids. “If producers are thinking about planting corn rootworm-resistant corn, they'll first want to make sure their buyer is willing to buy that corn,” says Alexander. “You wouldn't want to plant corn rootworm corn without checking with them, because it doesn't so much matter what the European Union wants, what really matters is what your buyer wants.”The Purdue study, “Determinants of Corn Rootworm Resistant Corn Adoption in Indiana,” can be read online at www.agbioforum.org/v8n4/v8n4a01-alexander.htm.
Purdue University Department of Agricultural Communication