WOOSTER, Ohio -- As the number of Ohio growers planting transgenic corn hybrids increases, Ohio State University Extension entomologists are reiterating the importance of following required Insect Resistant Management (IRM) guidelines.
Ron Hammond, an OSU Extension entomologist with the Ohio Agricultural Research and Development Center, anticipates increased acres of Bt hybrids next season to help control such insects as Western corn rootworm and European corn borer. But such hybrids need to be carefully managed with non-transgenic areas.
"Knowing that Ohio growers will, in all likelihood, plant more Bt corn hybrids next spring, we continue to remind growers about IRM requirements. The purpose of employing these practices is to help prevent insects from developing resistance to the Bt gene," said Hammond. "These are government regulations that must be followed. Growers who fail to follow IRM requirements risk losing access to corn biotechnology."
Transgenics is the science of introducing a gene from one organism or plant into the genome of another organism or plant. In crop production, Bt corn to control European corn borer and rootworm, and Round-Up Ready corn and soybeans for enhanced weed control would be examples of transgenics.
The most important requirement when using Bt corn hybrids is to plant a 20 percent refuge of non-transgenic corn.
"A refuge is simply a block or strip of corn planted with a hybrid that does not have the Bt gene. The primary purpose is to maintain a pest population that is not exposed to the Bt toxin, allowing susceptible insects to remain within the population and mate with any resistant insects that survive in the transgenic area," said Hammond. "This allows any offspring to remain susceptible to the Bt hybrid."
When managing the refuge, growers are urged to adhere to the following guidelines:
• In terms of distance of the refuge from the Bt corn for corn borer, the non-Bt refuge can be within, adjacent, or near the Bt field, but it has to be within a half-mile -- preferably within a quarter mile. For corn rootworm, the non-Bt refuge has to be within the same field as the Bt corn, or adjacent to it.
• There are several planting options, including a separate field refuge, mainly used to control corn borer; an adjacent field; a separate, but adjacent block next to the Bt corn; a block refuge within the Bt field; a refuge planted along the perimeter; or a split-planter refuge. "If planting the refuge using a split planter, the strip width must be at least four rows, preferably six rows," said Hammond.
• Both transgenic and non-transgenic areas should be managed in a similar manner. Growers should plant both hybrid types close to or at the same time, and select Bt and non-Bt hybrids that have similar growth and development characteristics. "If planting a refuge for corn rootworm, for example, the cropping history must be the same. That is, if Bt corn is planted following corn, then the refuge must be planted following corn," said Hammond.
• When using insecticides, there are procedures for controlling the target insect and secondary insects. When controlling for European corn borer, the non-Bt corn refuge may be treated with conventional insecticides only if the target pest reaches economic threshold. "A foliar Bt-based insecticide cannot be used within the refuge," said Hammond. When controlling for Western corn rootworm, a soil-, seed-, or foliar-applied insecticide is allowed for the refuge. If an aerial insecticide is applied to the refuge for control of rootworm adults, the same treatment must be applied at the same time to Bt corn.
• If a refuge is planted in a rotated field, the Bt field must also be planted on rotated ground. However, if the refuge is corn following corn, the Bt field can be planted on either a continuous or rotated field.
Guidelines also exist when planting a hybrid with stacked traits that contain both Bt types.
"Growers have two management approaches. The first choice is to plant separate refuges for each target pest," said Hammond. "We recommend the second choice -- the common refuge approach where corn without any Bt technology is planted. In this case, a 20 percent refuge must be planted within or adjacent to the transgenic field."
Hammond said that growers should consult their seed dealers for information regarding properly managing for transgenic corn hybrids, or for any additional IRM requirements related to single and stacked-trait corn hybrids.
According to the U.S. Department of Agriculture, over 40 percent of Ohio's 2007 corn crop consisted of biotech varieties, 15 percent more than last year. Of the three main biotechnology types -- insect resistant, herbicide resistant, and stacked genes -- farmers grew more stacked gene varieties, increasing their acreage by 15 percent over last year. Transgenic corn production has been slowly increasing in Ohio since 2003.