Pioneer Hi-Bred International is reminding growers about planting Bt refuges as part of the effort to control corn borer and corn rootworm over the long term. The best way to do that, the company notes, is to make sure a few of the pests survive in the short term. But, there is no one-size-fits-all approach to refuge management, according to Murt McLeod, agronomy research scientist for Pioneer. He offers some tips for getting the most from your Bt refuges.
Refuges protect the technology by allowing susceptible insects to mate with any survivors from Bt fields. The resulting offspring will reduce the chance that resistance will continue.
"The options that work best will vary among growers. Find the one that is most efficient in your operation and stick with it," McLeod says. "There are many different configurations that can be used, from adjacent blocks to strips within the field or around the perimeter."
Pioneer recommends the following refuge management guidelines for growers:
Sizes. The size of the refuge, for both corn borer Bt and corn rootworm Bt products, must equal 20% of the corn acres planted. In cotton-growing regions the size of the refuge should equal 50% 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.
McLeod notes that planting hybrids with stacked Bt genes, Herculex RW rootworm protection and Herculex I insect protection for example, requires an extra management step.
"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% 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.