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By
Jim Griffin
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A major
component of our weed research program in the LSU AgCenter involves
the evaluation of new herbicides in development by chemical
companies. Envoke,
common name trifloxysulfuron-sodium, is in
the sulfonylurea chemical family and has a unique mode of action
unlike any other herbicide currently used in sugarcane.
Research in
Louisiana
with Envoke (formerly CGA 362622) was first initiated in
1999. Provided in this
article is information related to Envoke, which was labeled for use
in sugarcane in 2004.
General
Information on the Envoke Label
Envoke can be applied postemergence overtop to plant or ratoon
cane up to 24 inches tall at a rate on a broadcast basis of 0.3 oz
product/A or as a directed application at 0.3 to 0.6 oz product/A to
sugarcane 18 inches tall up through layby.
As a directed application spray should be directed away from
the upper plant parts (whorl) so as to minimize contact with the
crop, yet to maximize contact with the target weeds.
Add to the finished spray solution a high quality nonionic
surfactant with a minimum of 80% surface-active agent at 0.25%
volume/volume (1 qt/100 gallons) if applied overtop of cane and
either a nonionic surfactant or a nonphytotoxic crop oil concentrate
containing 15 to 20% approved emulsifier at 0.5 to 1.0%
volume/volume (2 to 4 qt/100 gallons) if directed underneath the
crop. For ground
application use a minimum of 10 gallons of water per acre (broadcast
basis). Higher volumes
(at least 20 gallons per acre) should be used for severe weed
infestations to ensure adequate spray coverage.
Envoke can not be applied aerially.
Envoke gets into the plant very quickly and is rain-fast
within 3 hours after application.
Based on the label, Envoke at 0.3 oz/A will control seedling
johnsongrass up to 6 inches, rhizome johnsongrass up to 10 inches
(partial control), itchgrass up to 4 inches, morningglories
(tie-vines) up to
4 to 5
inches, and
purple and yellow nutsedge up to 6 inches.
Leaves of susceptible plants normally turn yellow, red, or
purple after several days followed by necrosis and death of the
growing point. Weed
death generally occurs 1 to 3 weeks after application depending on
species and growing conditions.
Our research shows that Envoke even at 0.6 oz/A is not
effective on large rhizome johnsongrass (more than 18 inches).
We have seen, however, that combinations of Envoke with
Asulox/Asulam can provide complementary broadleaf and grass weed
control. Specifically, Envoke
at 0.3 oz/A applied with Asulox/Asulam at 2 qt/A (half rate) has
provided control of large rhizome johnsongrass equal to or better
than Asulox/Asulam applied alone at the full rate, with the added
advantage of controlling other weeds.
Envoke applied overtop
of sugarcane can cause some yellowing and white banding on leaves
present in the whorl at application as well as slight stunting but
recovery is rapid and no negative effect on sugarcane yield has been
observed.
General Precautions
or Restrictions Specified on the Envoke Label
Do not exceed a maximum of 3 applications or a total of 1.5
oz/A per season.
Do not apply
Envoke within 100 days of sugarcane harvest.
Make sequential
applications at least 14 days apart.
Do not apply to
sugarcane under stress due to drought, standing water, heavy insect
and/or disease pressure, low soil fertility, etc.
For the time being you should follow the same guidelines as
specified for Asulox/Asulam and
DO NOT cultivate, fertilize or otherwise disturb the johnsongrass
root system 7 days before or after Envoke application.
Based on research conducted from 1999 to 2003 Envoke would have a
fit in
Louisiana
sugarcane when
applied:
1)
Overtop in combination with Asulox (April/May or Fall application) for
control of large rhizome johnsongrass and other weeds
2)
Overtop alone if weeds are small
3)
After layby as a directed application for morningglory, small johnsongrass,
itchgrass, and nutsedge control
4)
Overtop after planting for johnsongrass, itchgrass, morningglory, and
nutsedge control
Envoke is not a stand alone herbicide where large rhizome
johnsongrass is a problem and a combination with Asulox/Asulam would
be needed. Sugarcane
injury is not of concern with single applications made overtop in
March through May. Even
though Envoke is labeled for postemergence application it does have
some soil activity. The
level of soil activity with Envoke will be evaluated this year.
Based on what we know at this time, other herbicides should
be used either in combination or as separate applications if
residual weed control is desired.
It is my understanding that Envoke will sell for around $7
per 0.1 oz product.
We will be looking closely at
weed control programs with Envoke this year and should have more
research-based recommendations after this season.
If you have questions concerning Envoke please feel free to
contact me.
________________________________________________________
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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