Wooster, Ohio
November 1, 2007
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. |
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