UNITED
STATES
ENVIRONMENTAL
PROTECTION
AGENCY
WASHINGTON,
D.
C.
20460
OFFICE
OF
PREVENTION,
PESTICIDES
AND
TOXIC
SUBSTANCES
MEMORANDUM
SUBJECT:
Addendum
to
Chlorsulfuron
Benefits
Discussion
for
Aerial
Applications:
Alternatives
Analysis
for
Winter
Wheat;
D313380
FROM:
Nicole
Zinn,
Biologist
Biological
Analysis
Branch
Jin
Kim,
Economist
Economic
Analysis
Branch
Biological
and
Economic
Analysis
Division
(
7503C)

THRU:
Arnet
Jones,
Chief
Biological
Analysis
Branch
David
Widawsky,
Chief
Economic
Analysis
Branch
Biological
and
Economic
Analysis
Division
(
7503C)

TO:
Susan
Jennings,
Chemical
Review
Manager
Mike
Goodis,
Branch
Chief
Special
Review
and
Reregistration
Division
PEER
REVIEW
PANEL:
April
27,
2005
SUMMARY
SRRD
requested
that
BEAD
provide
an
alternatives
analysis
for
chlorsulfuron
use
on
major
crops
in
major
use
areas
as
part
of
the
RED
process
for
this
chemical.
As
agreed
upon
with
SRRD,
BEAD
focused
this
analysis
on
winter
wheat
grown
in
Kansas
and
Oklahoma.
BEAD
believes
that
plant
growth
regulators
and
sulfonylureas
are
likely
alternatives
for
chlorsulfuron,
among
which
BEAD
believes
that
2,4­
D
or
metsulfuron
are
the
most
likely
alternatives.
There
are
a
number
of
other
plant
growth
regulators
and
sulfonylurea
herbicides,
as
well
as
combination
products,
available
that
may
also
be
used.
The
treatment
cost
of
alternatives
does
not
appear
to
be
significantly
different
from
the
treatment
cost
of
chlorsulfuron
and
2
chlorsulfuron+
metsulfuron.
Therefore,
pesticide
choice
by
growers
to
control
weeds
would
also
depend
on
such
factors
as
the
product
efficacy,
method
of
application,
and
other
application
costs;
however,
we
did
not
quantify
them
in
this
analysis
due
to
data
and
time
constraint.

INTRODUCTION
Chlorsulfuron
is
a
sulfonylurea
herbicide
and
is
an
acetolactate
synthase
(
ALS)
inhibitor
(
inhibits
amino
acid
biosynthesis).
Chlorsulfuron
is
registered
to
control
broadleaf
weeds
on
cereal
grains,
pasture,
rangeland,
industrial
turf
and
non­
cropland.
Risks
of
concern
have
been
identified
for
non­
target
plant
species
for
the
following
sites:
barley,
oats,
wheat,
pasture,
rangeland,
and
fallow
land.
Additional
information
on
aerial
application
and
the
other
sites
is
included
in
Chlorsulfuron
Benefits
Discussion
for
Aerial
Applications;
D313383.
This
assessment
assumes
that
chlorsulfuron
is
no
longer
available
in
order
to
portray
a
"
worst­
case"
scenario.

ALTERNATIVE
ANALYSIS
As
discussed
in
the
Chlorsulfuron
Benefits
Discussion
for
Aerial
Applications,
chlorsulfuron
is
used
on
<
0.5
percent
of
barley
acreage,
2
percent
of
oats
acreage,
1
percent
of
spring
wheat
acreage,
and
10
percent
of
winter
wheat
acreage
(
Zinn
and
Kim,
2005).
Chlorsulfuron
is
applied
to
18
percent
of
the
winter
wheat
acreage
in
Oklahoma
and
Kansas,
which
have
6,000,000
and
9,600,000
planted
acres,
respectively.
This
analysis
will
focus
on
winter
wheat
in
Oklahoma
and
Kansas
since
it
is
the
crop
with
the
highest
proportion
of
treated
acreage.
Additional
data
on
other
use
sites
and
other
states
is
available
in
the
benefits
discussion
mentioned
above.

Winter
Wheat
Chlorsulfuron
is
one
of
the
most
commonly
applied
herbicides
in
winter
wheat
(
See
Table
1).
Harvested
acres
for
the
surveyed
states
were
22.2
million
acres
(
NASS,
2003).

Table
1.
Percent
of
Winter
Wheat
Treated
with
Herbicides
in
U.
S.,
Oklahoma,
and
Kansas,
2002
Herbicide
%
Acres
Treated
(
U.
S.)
%
Acres
Treated
(
OK)
%
Acres
Treated
(
KS)
2,4­
D
13
8
6
Metsulfuron­
methyl
13
19
16
Chlorsulfuron
10
18
18
Sulfosulfuron
6
13
3
Tribenuron­
methyl
5
N/
A
N/
A
NASS
Agricultural
Chemical
Usage,
Field
Crop
Summary
2002,
May
2003
Chlorsulfuron
(
Glean
®
)
is
registered
for
control
of
broadleaf
weeds.
In
addition,
a
few
grass
weeds
are
included
on
the
label.
Although
there
are
many
weeds
controlled
or
suppressed
with
chlorsulfuron,
some
of
the
most
commonly
targeted
weed
species
by
chlorsulfuron
products
in
Oklahoma
and
Kansas
are
wild
mustard,
wild
buckwheat,
redroot
pigweed,
kochia
and
henbit
3
(
EPA
proprietary
data).
These
weeds
are
all
on
the
chlorsulfuron
label.
However,
of
these
weeds,
the
chlorsulfuron
label
only
claims
partial
control
of
kochia
and
wild
buckwheat.
The
Crop
Profile
for
Winter
Wheat
in
Kansas
mentions
henbit,
wild
buckwheat,
and
kochia
as
common
weeds
in
wheat
fields
(
Crop
Profile
for
Winter
Wheat
in
Kansas,
1999).

Chlorsulfuron
is
often
applied
in
combination
with
metsulfuron­
methyl
as
the
product,
Finesse
®
.
In
addition,
the
product
chlorsulfuron
+
flucarbazone­
sodium
(
Finesse
®
Grass
and
Broadleaf)
is
registered
in
several
states.
This
herbicide
controls
grass
and
broadleaf
weeds
on
wheat
(
Medlin,
2005).
According
to
Dallas
Peterson,
Extension
Weed
Scientist,
Kansas
State
University,
growers
will
continue
to
use
ALS
inhibitor
herbicides
if
chlorsulfuron
is
not
available
(
Peterson,
2005).

Using
proprietary
data,
BEAD
determined
which
herbicides
are
used
to
control
those
weeds
most
commonly
targeted
by
chorsulfuron
in
Kansas
and
Oklahoma.
For
each
weed,
Finesse
®
(
the
combination
product
containing
chlorsulfuron
and
metsulfuron)
was
most
frequently
used
to
target
these
weeds.
The
other
herbicides
used
to
control
these
weeds
were
other
sulfonylureas
and
plant
growth
regulators,
as
indicated
in
Table
2
below.
Although
there
are
many
alternatives
for
these
weeds,
only
the
most
common
alternatives
are
included
in
Table
2.
Table
2
also
shows
the
average
treatment
cost
per
acre
for
these
herbicides.

Based
on
this
list,
comments
received
during
the
RED
process,
and
discussions
with
extension
specialists,
BEAD
believes
that
growth
regulators
and
sulfonylureas
are
likely
alternatives
for
chlorsulfuron
on
winter
wheat,
among
which
BEAD
particularly
believes
that
2,4­
D
or
metsulfuron
are
most
likely
alternatives.
There
are
a
number
of
other
growth
regulators
and
sulfonylurea
herbicides,
as
well
as
combination
products,
available
that
may
also
be
used.
The
treatment
cost
of
alternatives
does
not
appear
to
be
significantly
different
from
the
treatment
cost
of
chlorsulfuron
and
chlorsulfuron+
metsulfuron.
Therefore,
pesticide
choice
by
growers
to
control
weeds
would
also
depend
on
such
factors
as
the
product
efficacy,
method
of
application,
and
other
application
costs;
however,
we
did
not
quantify
them
in
this
analysis
due
to
data
and
time
constraint.

Mesosulfuron­
methyl,
registered
in
2004
for
use
on
wheat,
has
some
limited
overlap
with
chlorsulfuron.
This
herbicide
is
registered
for
control
of
grass
weeds,
but
the
label
does
include
some
broadleaf
weeds,
including
control
of
wild
mustard
and
suppression
of
henbit
and
redroot
pigweed.
4
Table
2.
Herbicides
Commonly
Used
for
Certain
Weed
Species
in
Oklahoma
and
Kansas
Winter
Wheat
and
Treatment
Costs
per
Acre*
Pest
Species
Herbicides
Commonly
Used
Average
Treatment
Cost
per
Acre**
Wild
Mustard
Chlorsulfuron
Chlorsulfuron+
metsulfuron
2,4­
D
Metsulfuron
Dicamba
Dicamba+
traisulfuron
$
2.1
­
$
5.6
$
2.3
­
$
5.0
$
0.8
­
$
2.6
$
1.3
­
$
5.0
$
1.3
­
$
4.1
$
2.5
­
$
5.1
Wild
Buckwheat
Chlorsulfuron
Chlorsulfuron+
metsulfuron
2,4­
D
Glyphosate+
2,4­
D
Dicamba
Metsulfuron
$
2.1
­
$
5.6
$
2.3
­
$
5.0
$
0.8
­
$
2.6
$
7.1
$
1.3
­
$
4.1
$
1.3
­
$
5.1
Redroot
Pigweed
Chlorsulfuron
Chlorsulfuron+
metsulfuron
2,4­
D
Metsulfuron
Dicamba
$
2.1
­
$
5.6
$
2.3
­
$
5.0
$
0.8
­
$
2.6
$
1.3
­
$
5.0
$
1.3
­
$
4.1
Kochia
Chlorsulfuron
Chlorsulfuron+
metsulfuron
2,4­
D
Metsulfuron
Dicamba
$
2.1
­
$
5.6
$
2.3
­
$
5.0
$
0.8
­
$
2.6
$
1.3
­
$
5.0
$
1.3
­
$
4.1
Henbit
Chlorsulfuron
Chlorsulfuron+
metsulfuron
2,4­
D
Sulfosulfuron
Dicamba+
triasulfuron
$
2.1
­
$
5.6
$
2.3
­
$
5.0
$
0.8
­
$
2.6
$
6.7
­
$
8.0
$
2.5
­
$
5.1
*
This
is
not
the
complete
list
of
herbicides
used
to
control
the
target
weed
species
but
a
subset
of
the
more
commonly
use
herbicides.
**
EPA
Data
from
2001
to
2003
5
REFERENCES
EPA
proprietary
data.

Medlin,
Case,
Extension
Weed
Specialist,
Oklahoma
State
University,
February
15,
2005,
Personal
communication
with
Nicole
Zinn.

NASS
Agricultural
Chemical
Usage,
Field
Crop
Summary
2002,
May
2003
Peterson,
Dallas,
Extension
Weed
Science,
Kansas
State
University,
February
15,
2005,
Personal
communication
with
Nicole
Zinn.

USDA
Crop
Profile
for
Wheat
in
Kansas,
1999,
Web
address:
http://
www.
ipmcenters.
org/
cropprofiles/
docs/
KSwheat.
html
Zinn,
Nicole
and
Jin
Kim,
2005,
Chlorsulfuron
Benefits
Discussion
for
Aerial
Applications,
D313383.
