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By
Jim Griffin
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Weed
pressure in sugarcane fields right now in mid-January ranges from
nothing to a mat of green vegetation completely covering the rows.
In most cases weed pressure is greatest in fields where
sugarcane residue was burned early in the season and in plant cane
where herbicides just ran out. In
fields where sugarcane residue is still present it is doing a good
job of suppressing weed emergence.
This positive attribute of crop residue, however, also can be
negative when considering the crop.
Research conducted by USDA researchers in
Houma
over several years clearly shows that a sugarcane yield reduction of
4 to 5 tons per acre can occur if crop residue is not removed.
If you have fields right now that can be burned then do so as
soon as possible, preferably by mid February.
In fields where winter weeds are present take a close look to
see exactly what you have. Generally
the winter weeds present in fields will include some combination of
the following: buttercups, chickweeds, clovers/medics, common
dandelion, cressleaf groundsel (yellow top), curly dock, cutleaf
eveningprimrose, geranium, henbit, marestail, purslane speedwell,
shepherdspurse, smallflower bittercress, sowthistle, swine cress,
Virginia pepperweed, geranium, annual bluegrass, rescuegrass,
ryegrass, and timothygrass.
In general winter broadleaf weeds are easier to control than
grasses. It is important
not so much to know what specific weed you have but rather how much
winter grass is present.
This is because a significant presence of grasses in the mix
will require that paraquat (Gramoxone Extra, Gramoxone Max, or Boa)
be applied. For
broadleaf weeds 2,4-D, Weedmaster, Brash, or Kambamaster are
generally very effective. Winter
weeds if not removed can slow warming and drying of sugarcane beds,
interfere with tillage operations, and hinder emergence and early
season growth of sugarcane. Winter
weeds need to be removed to maximize yield potential of the crop.
Consideration also should be given right now to bermudagrass.
Although not a winter weed, bermudagrass can be an aggressive
competitor with sugarcane as the crop is emerging in the spring.
I have heard complaints that herbicides applied at planting
last year just gave out after about eight weeks and bermudagrass
reinfested some planted cane. The
“breaking” of the herbicide was not just restricted to a single
herbicide. The reality
is that for any herbicide to control bermudagrass longer than eight
weeks in moist soil when soil temperatures are high is asking a lot.
In the sugarcane weed control guide provided through the LSU
AgCenter we are careful in using the word “control” with any
herbicide for bermudagrass. Suppression
is a better term although we have seen excellent suppression/control
in some cases. It
appears that the most displeasure with herbicides applied at
planting last year in regard to bermudagrass control was where a
good fallow program combining glyphosate (Roundup products) and
tillage was not used. Bermudagrass
control in sugarcane involves a program approach that starts in the
fallow year. This topic
will be discussed at a later date.
The jury is still out as to what will be the long term consequence
in those plant cane fields where bermudgrass was present going into
the winter. The
herbicide applied at planting may not have controlled bermudagrass
but there is no way of knowing if bermudagrass root systems and
rhizomes (underground stems) were developed enough for plants to
survive the winter dormant period.
The cold weather and wet soil conditions have definitely put
a hurt on bermudagrass and we might be surprised as to how well the
herbicides performed when conditions are conducive to weed regrowth
in the spring.
One thing is for certain, once bermudagrass has emerged from the
winter dormant period it is impossible to control with herbicides
that we have available. The
good news is that we have a second opportunity to suppress or even
control bermudagrass if we apply certain herbicides early enough.
Contrary to what you are accustomed to, you might want to
consider a January or early February application of Dupont K4 or
Command plus Direx. The
purpose for the early application is get the chemical in the soil
and around the root system of bermudgrass before it begins to regrow.
The question is often asked if this early application will
result in the herbicide running out of gas before layby.
This should not be a problem especially with the shift in
recent years toward earlier layby.
Cool soil temperatures in late winter will prolong the life
of a herbicide and herbicide applied in January or February will
last much longer than when applied in August.
The bottom line here is simple – the only option that you
have to effectively manage bermudagrass is to apply herbicide in
January or early February before the weed initiates new
growth. A later
application in March may slow bermudagrass growth but it will
recover quickly.
Provided below are specific weed control recommendations for three
scenarios.
Scenario #1 - Fields with crop residue present and sparse
winter weeds – Remove the crop residue as soon as possible either
by burning or by using an implement (Broussard, Lawson, Orthman, or
Sunco or brush). Keep in
mind that use of a “trash removing” implement will clean the row
top but will move the residue into the row middles.
This additional residue in the row middles could interfere
with tillage operations in the spring but also could offer benefits
in non-rutted fields if you plan to reduce or eliminate spring
tillage operations. Research
is underway to evaluate mechanical removal of crop residue versus
burning and how this might fit in reduced tillage programs.
Scenario #2 - Fields with broadleaf and/or grass winter weeds
and where you suspect that bermudagrass will not be a problem
– It is not critical that you get into those fields right now.
Herbicides can be applied in late February or early March but
don’t delay too long. Smaller
weeds are easier to control and die faster than larger weeds.
If you have only broadleaf weeds 2,4-D at 2 qt/A or
Weedmaster/Brash/Kambamaster at 1 qt/A can be applied broadcast when
air temperature is above 65°
F. These rates could be
adjusted downward somewhat depending on the size of the weeds and
whether or not another herbicide is added.
Aatrex/Atrazine, Direx/Karmex, or Spartan may be added to
improve weed control and to provide soil residual activity.
You could also choose to apply the herbicides on a band and
use tillage to control weeds in the middles.
Scenario #3 - Fields with broadleaf and/or grass winter weeds
and where you suspect that bermudagrass will be a problem.
You should apply Dupont K4 at 4 lb/A or Command at 3 pt/A
plus Direx in January or early February.
It is better to be too early than too late.
Whether to apply the herbicide on a band or broadcast is a
decision that will depend on how much you are willing to spend and
your specific management program.
If you plan to eliminate spring tillage in plant cane and in
non-rutted stubble fields it would be advisable to broadcast
herbicide. If winter
broadleaf weeds are present, 2,4-D, Weedmaster, Brash, or
Kambamaster can be applied with Dupont K4 or Command/Direx.
If ryegrass or other grass weeds are present, Gramoxone
Extra, Gramoxone Max, or Boa should be included as described for
Scenario #2.
The intent of this article is to provide you with a starting point
to think about planning your weed control program.
A meeting with your county agent or consultant may help to
develop or to fine tune a weed control program specific to your
needs.
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Dr. Jim
Griffin is with the LSU AgCenter in the Department of Agronomy and
Environmental Management and has research and extension
responsibilities in the area of sugarcane weed management.
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