Replanting Corn: How To Control Corn Plants From The Initial Planting
CHAMPAIGN, ILL.
Certain areas of Illinois received excessive
precipitation over the Memorial Day weekend,
and it appears likely that some corn
replanting will occur when field conditions improve.
Losses of the initial corn stand will likely
range from complete to partial, so farmers may
need to implement practices to control any remaining
corn plants before replanting. What options
are available to control emerged corn from
a first planting?
Tillage can effectively remove corn plants remaining
from the first planting, regardless of
their herbicide sensitivity or resistance characteristics.
This option introduces very little risk
of injury to the replanted corn, unlike some herbicide
alternatives described in the following
paragraphs. Tillage also can effectively control
any weeds that might have emerged in the first
planting, providing weed-free conditions into
which to replant. However, for myriad reasons
farmers may not want to disturb the soil prior to
replanting and thus look to herbicide alternatives.
If herbicides will be used, they should be
applied before the fields are replanted.
Glyphosate is very effective at controlling existing
stands of (sensitive) corn. There is no waiting
interval between application and replanting
specified on the label, but overall control may be
improved if at least 24 hours elapses between
application and replanting. Glyphosate would
also control most emerged weeds, allowing replanting
into weed-free conditions. However,
glyphosate obviously would not control existing
stands of glyphosate-resistant corn (or any
glyphosate-resistant weeds that might already
have emerged), so alternative herbicides would
be required.
Poast, Poast Plus, Fusion, Fusilade, Select,
and Assure II are effective for controlling volunteer
corn (including volunteer glyphosate-resistant
corn) in soybean, but each product label
includes an interval that must elapse between
application and rotation to or replanting with
grass crops, such as corn. These intervals range
in days from 30 (Poast, Poast Plus, Select) to 60
(Fusion, Fusilade) to as many as 120 (Assure II),
making these products unlikely choices for this
particular use.
We have evaluated several different herbicides
or herbicide combinations for control of an existing
stand of corn. Some results from this research,
conducted in 2006 and 2007, are
summarized in Table 1. Treatments that included
glufosinate, paraquat, or isoxaflutole
often appeared to be providing good control at 7
days after application, but corn frequently recovered
by the evaluation 14 days after application.
SelectMax has a supplemental label for control
of an existing stand of glyphosate-resistant corn
prior to replanting field corn. The label allows
applications of 6 fluid ounces per acre for control
of glyphosate-resistant field corn up to 12
inches tall. We have limited research experience
with this particular rate of SelectMax, but we
have observed good to excellent control of corn
with a 4-ounce rate of SelectMax. Applications
should include NIS and AMS (do not use a COC
or MSO in this particular use), and care must be
taken to avoid in-field overlaps, or excessive injury
to the replanted corn may occur. Do not replant
fields treated in this way sooner than 6
days after application. Previous research has
shown that clethodim, the active ingredient in
SelectMax, has some soil persistence and can
cause significant damage to corn when applied
at higher rates prior to planting. It is strongly
advised that rates not exceed the rate labeled for
this type of application, that in-field overlaps be
avoided, and that the 6-day waiting interval be
fully expired before treated fields are replanted.Δ