Columbus, Ohio
March 1, 2007
Planting continuous corn may
promote greater weed control problems, but growers can stave off
any serious issues as long as they follow the best management
strategies for their situation.
“Rotation of crops has historically resulted in greater
diversity in herbicide use. Planting a monoculture of corn, or
even soybeans, can result in greater weed problems over the long
term, due to the propensity for overuse of certain herbicides
that weeds can become resistant to,” said Mark Loux, an
Ohio State University Extension
weed specialist. “However, we are not convinced that the
planting of continuous corn really poses more serious issues for
weed management, compared with a crop rotation, as long as
appropriate weed management strategies are used.”
Loux offers the following considerations for weed management in
a continuous corn system to most effectively control tough weeds
and minimize selection for herbicide resistance.
- Use tillage or pre-plant
burndown herbicides to ensure that corn is planted into a
weed-free seedbed. Loux said doing so may help growers avoid
issues of glyphosate resistance that have impacted other
crop systems. “Planting soybeans into weedy fields, and
delaying the first glyphosate application until sometime
after soybeans emerge, contributed to the development of
glyphosate resistance in giant ragweed and marestail, and
also the general increase in winter annual weeds and
dandelions,” said Loux, who also holds an Ohio Agricultural
Research and Development Center appointment.
- Select an herbicide
program that is appropriate for the weeds in the field. “A
total pre-emergence herbicide program can control many
annual weeds, but frequently fails to provide season-long
control of weeds that can emerge in mid-season, such as
dense annual grass infestations, giant ragweed, burcucumber,
and perennial weeds,” said Loux. “A combination of
pre-emergence and post-emergence herbicide applications is
more effective for these type of weeds, and in any field
with a history of poor weed control.”
- Use a diversity of
herbicide sites of action to reduce the risk of herbicide
resistance. “This is more easily accomplished where a
combination of pre-emergence and post-emergence herbicides
are used, compared with a total pre-emergence or
post-emergence approach,” said Loux. “For example, avoid
using atrazine as the sole broadleaf herbicide in continuous
corn, and avoid continued use of ALS inhibitors for control
of the same weeds every year.”
- Use other herbicides in
conjunction with glyphosate programs to reduce the chance of
glyphosate resistance. “Some examples: apply pre-emergence
herbicides at the time of planting to reduce the weed
population that will need to be controlled with
post-emergence glyphosate applications; in a tilled field
where a total post-emergence program is planned, mix
glyphosate with other herbicides that can help control
emerged weeds and provide residual weed control; and where
glyphosate is applied late post-emergence following
pre-emergence herbicides, mix it with low rates of other
post-emergence herbicides,” said Loux.
- Manage post-emergence
glyphosate applications appropriately, and apply when weeds
are small.
- Consider using Liberty
Link herbicide in post-emergence applications instead of
glyphosate when planting corn hybrids with the BT Herculex
trait, or when planting stacked hybrids that are resistant
to both glyphosate and BT Herculex. “There is about a $6 per
acre difference in cost between glyphosate and Liberty, but
use of Liberty breaks the cycle of continuous glyphosate
use, and this can have long-term benefits,” said Loux.
- Consideration should be
given to the type of corn that is used each year in a
continuous corn system. “From a herbicide use standpoint,
growers have a choice of conventional hybrids;
glyphosate-resistant hybrids; Liberty Link hybrids; and
stacked-trait hybrids,” said Loux. “Rotation of these types
of corn from year to year, and corresponding rotation of
herbicides, should reduce the risk of resistance to
glyphosate and other herbicides.”
- Consideration should be
given to the rotation of corn hybrids to minimize the risk
from volunteer corn, which could be herbicide-resistant and
pose a weed problem.
For more information on managing
weeds in continuous corn systems, or to learn more about
continuous corn production, log on the OSU Extension Agronomy
Crops Team Web site at
http://agcrops.osu.edu. |
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