One key to controlling corn borer and corn rootworm over the long-term is to make sure a few of them survive in the short-term. Pioneer Hi-Bred International, Inc., reminds growers planting Bt (Bacillus thuringiensis) corn this spring to comply with recommended refuge area guidelines.
A refuge is an effective way to allow susceptible insects to mate with any survivors from Bt fields. Resulting offspring will reduce the chance that resistance will continue.
There is no one-size-fits-all approach to refuge management, notes Murt McLeod, agronomy research scientist for Pioneer.
"We need to continue to do a good job, and the way to do that is for growers to find what is most efficient in their operation," he says. "The options that work best will vary among growers. Find the one that is most efficient in your operation and stick with it."
A successful refuge begins with a careful reading of the product use guide and stewardship agreement.
"Be very familiar with the product use guide that lays out all the possibilities," says McLeod. "There are many different configurations that can be used, from adjacent blocks to strips within the field or around the perimeter."
Lance Bailey, product stewardship manager for Pioneer, adds that as planting time approaches, now is a good time to brush up on the basics of good refuge management.
"Most corn growers already do a good job of developing refuges as part of stewardship compliance agreements," says Bailey. "We have a high level of compliance with all of our Bt technology in the marketplace."
To continue the high level of compliance, growers should keep the following refuge management tips in mind this growing season.
• Sizes. The size of the refuge, for both corn borer Bt and corn rootworm Bt products, must equal 20 percent of the corn acres planted. In cotton-growing regions the size of the refuge should equal 50 percent of a grower's corn acres.
• Location. 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.
• Hybrid selection. 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 also will allow growers to harvest both at the same time. It is especially important to match the hybrids in maturity, early vigor and plant height.
• Herculex insect protection. Planting hybrids with stacked Bt genes, Herculex RW rootworm protection and Herculex I insect protection, requires an extra management step, McLeod says.
• "If you plant corn hybrids with the Herculex XTRA trait, be sure you have a refuge block for both the corn rootworm component and for the lepidopteron aspect," he says. "Don't forget to do both."
• When planting corn hybrids with the Herculex XTRA trait, two refuge options exist. A common refuge is designed to address both corn borers and corn rootworms with one refuge, whereas a separate refuge is designed to control each insect independently. In non-cotton growing areas, a common refuge must equal 20 percent 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 percent corn borer refuge that cannot contain a Bt protein active against corn borer and a 20 percent rootworm refuge that can not contain a Bt protein active against rootworm. The corn borer refuge must be within one-half mile of the Bt field. The corn rootworm refuge must be in the same field or adjacent to the Bt hybrids.
• Crop management. 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.
• Monitor. 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.
• Stay up to date. "Different technologies have different requirements, which can lead to confusion," says Bailey. "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."