UNITED
STATES
ENVIRONMENTAL
PROTECTION
AGENCY
WASHINGTON,
D.
C.
20460
OFFICE
OF
PREVENTION,
PESTICIDES
AND
TOXIC
SUBSTANCES
Memorandum
SUBJECT:
Benefits
Assessment
for
Disulfoton
Use
on
Potatoes
and
Radish
Seed
FROM:
Nikhil
Mallampalli,
Entomologist
Herbicide
and
Insecticide
Branch
Colwell
Cook,
Entomologist
Herbicide
and
Insecticide
Branch
Anthony
Gilbert,
Economist
Economic
Analysis
Branch
Biological
and
Economic
Analysis
Division
(
7503C)

THROUGH:
David
Brassard,
Senior
Scientist
Art
Grube,
Senior
Economist
Arnet
Jones,
Branch
Chief
Herbicide
and
Insecticide
Branch
David
Widawsky,
Branch
Chief
Economic
Analysis
Branch
Biological
and
Economic
Analysis
Division
(
7503C)

TO:
Christina
Scheltema,
Chemical
Review
Manager
Betty
Shackleford,
Branch
Chief
Reregistration
Branch
3
Special
Review
and
Reregistration
Division
(
7508C)

September
26,
2001
Summary
of
Analysis
This
assessment
investigates
the
pest
management
and
economic
benefits
of
the
use
of
liquid
disulfoton
in
potatoes
and
radishes,
in
the
context
of
mitigation
proposed
for
risks
faced
by
mixer/
loaders
and
applicators
of
this
insecticide.
Disulfoton
appears
to
have
very
different
benefits
in
the
production
of
each
of
these
crops.

In
potatoes,
while
disulfoton
has
historically
been
an
important
component
of
the
chemical
arsenal
used
against
aphid
pests,
its
use
in
the
past
two
years
or
so
has
declined
greatly.
It
is
now
used
on
a
small
proportion
of
the
total
US
crop,
though
in
some
areas,
particularly
Idaho,
it
remains
an
insecticide
of
some
importance.
This
reduction
in
use
is
largely
a
result
of
the
development
of
effective
alternative
insecticides.
As
long
as
the
currently
available
insecticide
options
exist,
however,
growers
should
still
be
able
to
achieve
adequate
control
of
pests,
though
perhaps
less
economically,
without
liquid
disulfoton.

In
radishes
grown
for
seed,
liquid
disulfoton
use
is
a
much
more
important
pest
management
tool
for
those
growers
operating
in
Washington
state.
Producers
in
this
region
face
aphid
pests
not
seen
in
other
areas,
and
have
many
fewer
chemical
alternatives
available
to
them,
as
compared
to
potato
growers.
The
economics
of
radish
seed
production
create
a
small
profit
margin
and
this
also
contributes
to
the
importance
of
disulfoton,
which
is
both
cheap
and
efficacious
in
its
liquid
form.
Thus,
in
this
crop,
and
for
this
region
in
particular,
liquid
disulfoton
use
has
critical
benefits
and
risk
mitigation
should
be
carefully
considered.

Background
Disulfoton
is
an
organophosphate
insecticide
used
on
a
wide
variety
of
crops
in
part
because
it
not
only
has
contact
toxicity
but
is
also
taken
up
by
plant
root
systems
and
remains
active
against
target
insects
for
a
relatively
long
time.
It
is
available
for
both
the
crops
addressed
here
in
both
liquid
and
granular
form.
Risk
modeling
by
the
Health
Effects
Division
indicates
that
this
chemical
may
pose
the
greatest
hazards
to
mixer/
loaders
and
applicators
if
the
liquid
form
is
applied
aerially
or
via
chemigation.
Furthermore,
the
liquid
form
is
more
hazardous
than
the
granular
form
(
regardless
of
application
method)
.
Therefore,
SRRD
has
asked
BEAD
to
investigate
the
importance
of
liquid
disulfoton
in
U.
S.
production
of
potatoes
and
radishes
grown
for
seed,
as
well
as
the
impacts
created
by
restrictions
on
these
pest
control
practices.

Role
of
disulfoton
and
chemical
alternatives
available
in
potato
production
Disulfoton
has
historically
been
used
as
one
of
many
insecticides
in
this
crop
to
control
aphid
infestations
across
the
U.
S.
The
main
targets
of
this
use
are
the
green
peach
aphid,
Myzus
persicae
,
and
the
potato
aphid,
Macrosiphum
euphorbiae
.
During
the
period
from
1987­
1998,
an
average
of
4
%
of
the
nation
 
s
potato
acreage
was
treated
with
this
chemical,
and
in
1999,
the
National
Potato
Council
asserted
in
a
letter
to
EPA
that
it
was
an
important
component
of
aphid
pest
management,
in
both
its
granular
and
liquid
forms.
In
addition
to
suppression
of
pest
populations,
disulfoton
is
also
used
to
manage
resistance
to
organophosphate
insecticides,
a
phenomenon
common
in
the
targeted
aphid
species.
Granular
disulfoton
is
applied
at
planting
to
control
early
season
aphid
populations.
A
subsequent
application
of
liquid
disulfoton
may
also
be
made
during
the
growing
season,
either
aerially,
by
ground
sprayers,
or
chemigation.
However,
the
latest
USDA/
NASS
statistics
available
indicate
that
in
1999,
an
average
of
only
a
single
application
was
used
in
the
states
surveyed
(
including
Colorado,
all
Pacific
Northwest
growing
regions,
Indiana,
Maine,
Minnesota,
North
Dakota,
Pennsylvania,
and
Wisconsin)
.
Since
1999,
the
average
U.
S.
acreage
treated
with
disulfoton
has
declined
to
1
%
(
USDA/
NASS
statistics,
2000)
.
Indeed,
in
some
states
(
Delaware,
Florida,
North
Carolina)
growers
apparently
no
longer
apply
this
insecticide,
and
it
is
not
listed
as
an
insecticide
option
in
crop
profiles
published
by
extension
services
in
these
states,
despite
current
registration
(
USDA
Crop
Profiles
for
Delaware,
Florida,
Ohio,
North
Carolina,
and
Pennsylvania)
.

In
Idaho,
however,
disulfoton
use
is
higher
than
the
national
average.
The
latest
published
information
indicates
that
4
%
of
the
total
acres
grown
were
treated
with
disulfoton
(
USDA
Crop
Profile)
.
This
use
appears
to
be
predominantly
of
the
liquid
form.
In
some
areas
of
Idaho
the
systemic
uptake
of
disulfoton
by
plants
translates
into
less
harmful
effects
on
beneficial
insects
such
as
pollinators,
which
are
important
in
adjacent
crops
such
as
alfalfa
(
A.
Schreiber,
R.
Stoltz,
pers.
comm
.
)
.
Some
growers
in
Washington
state
also
use
disulfoton,
for
the
same
reason
(
A.
Schreiber,
pers.
comm
.
)
.
Disulfoton
is
applied
aerially
in
these
regions
so
as
not
to
damage
potato
vines
(
as
would
occur
if
ground
spray
equipment
were
used)
.
In
Washington
an
estimated
90
%
of
disulfoton
applications
are
of
the
liquid
form,
applied
aerially
(
A.
Schreiber,
pers.
comm
.
)
.
No
such
information
has
been
provided
for
Idaho.

Reduction
in
disulfoton
use
in
recent
years
has
apparently
occurred
largely
because
of
the
registration
and
adoption
(
by
growers)
in
the
past
two
years,
of
other
insecticides
for
similar
purposes
in
potato
(
A.
Schreiber,
R.
Stoltz,
M.
Aerts,
pers.
comm
.
)
.
These
include
imidacloprid,
pymetrozine,
and
thiamethoxam.
These
chemicals
join
a
set
of
other
insecticides
that
together
provide
adequate
control
of
the
target
pests
in
most
regions
of
production.
Information
provided
by
extension
service
contacts
in
Florida
suggest
that
the
insecticides
that
are
currently
used
most
commonly
against
the
aphid
pests
principally
targeted
by
disulfoton
are
methamidophos,
aldicarb,
and
imidacloprid
(
M.
Aerts,
pers.
comm
.
)
.
Like
disulfoton,
both
imidacloprid
and
methamidophos
have
good
systemic
activity
against
aphids
(
Crop
Profiles
for
Wisconsin,
Idaho)
.
Furthermore,
imidacloprid,
in
particular,
also
controls
other
pests,
such
as
the
Colorado
potato
beetle
and
whiteflies,
that
often
occur
at
the
same
time
as
aphids
and
are
not
as
well
managed
with
disulfoton
(
Crop
Profiles
for
Florida,
Wisconsin)
.
These
aspects
have
probably
2
contributed
to
the
adoption
of
these
insecticides
for
pest
control
in
potatoes.

Role
of
disulfoton
and
chemical
alternatives
available
in
the
production
of
radishes
grown
for
seed
In
this
crop,
disulfoton
is
used
only
by
growers
in
the
Columbia
basin
area
of
Washington
state,
on
a
 
special
local
needs
 
(
(
24c)
label.
Radish
seed
is
a
minor,
but
economically
important
crop
for
producers
in
the
Columbia
Basin
of
Washington.
Production
from
here
is
utilized
domestically
and
internationally
for
growing
fresh
radishes
for
consumers.
Radish
seed
is
grown
in
regions
where
cool,
wet
seasons
consistently
predominate,
and
in
the
U.
S.
the
crop
has
historically
been
grown
in
the
Pacific
northwest
and
California
(
McGregor,
1976)
.
Further
information
on
the
current
extent
of
the
total
U.
S.
crop
are
not
available,
however,
as
it
does
not
appear
to
be
tracked
by
USDA
 
s
agricultural
surveys.
The
crop
is
an
annual
one,
and,
in
Washington,
it
is
planted
in
March
and
harvested
in
August
(
G.
Pelter,
pers.
comm
)
.
Disulfoton
use
is
targeted
toward
two
aphid
species,
the
cabbage
aphid
(
Brevicoryne
brassicae
)
and
the
turnip
aphid
(
Rhopalosiphum
pseudobrassicae
)
.
They
cause
premature
crop
senescence,
which
results
in
yield
loss
and/
or
loss
of
seed
quality.
They
also
make
harvesting
very
difficult
when
their
sticky
 
honeydew
 
(
(
excreta)
coats
machines.

Growers
operate
with
a
slim
profit
margin
and
produce
a
relatively
small
acreage
of
this
crop
­
635
acres
total
in
this
area
in
2000
(
G.
Pelter,
pers.
comm
.
)
.
As
a
result,
aphid
damage,
if
not
rigorously
controlled,
could
easily
be
catastrophic
for
individual
farmers.
Disulfoton
is
applied
in
both
granular
and
liquid
form
on
radishes
in
this
region,
and
virtually
all
acreage
receives
one
application,
early
in
the
growing
season
after
seed
stalks
form
on
plants.
Growers
usually
apply
the
insecticide
themselves
(
G.
Pelter,
pers.
comm
)
.
Liquid
disulfoton
is
applied
as
a
soil
injection
in
combination
with
a
fertilizer.
The
application
to
an
average
field
(
typically
20
to
25
acres
in
size)
takes
an
estimated
four
hours
at
most.
Thus,
a
grower
would
be
typically
exposed
to
disulfoton
only
once
annually,
and
only
during
mixing­
loading
operations
(
G.
Pelter,
pers.
comm
.
)
.

Pirimicarb,
chlorpyrifos,
pymetrozine
are
the
only
registered
chemical
control
alternatives
available
to
growers
for
these
insect
pests.
Pirimicarb
is
already
used
once
to
control
late­
season
infestations
of
these
aphids,
if
at
all.
Chlorpyrifos
cannot
be
used
during
bloom,
when
aphids
can
occur,
due
to
toxicity
to
honey
bees
that
pollinate
this
and
other
nearby
crops.
Pymetrozine
is
relatively
expensive
and
does
not
provide
good
lower
canopy
control.
Disulfoton
is
also
advantageous
in
that
it
allows
predatory
and
parasitic
insects
to
develop
in
seed
radish
fields,
since
other
insecticides
are
not
utilized
until
later
in
the
growing
season
(
if
at
all)
.
As
a
result
disulfoton
is
considered
an
important
part
of
the
industry'
s
IPM
program
(
G.
Pelter,
pers
.
comm
.
)
.

Economic
impact
of
mitigation
of
disulfoton
risks
in
potato
Curtailing
liquid
application
of
disulfoton
could
motivate
growers
to
switch
to
other
registered
alternatives,
such
as
imidacloprid,
or
increase
the
applications
of
methamidophos
in
addition
to
the
current
pesticide
control
regime.
In
order
to
estimate
the
economic
impact
to
the
potato
industry,
disulfoton
was
compared
with
methamidophos
and
imidacloprid
using
a
five
year
historical
range
of
production
costs
and
grower
revenues.
Washington
State,
Idaho
and
Wisconsin
were
selected
for
this
analysis.
In
2000,
these
three
states
together
harvested
over
60
%
of
the
total
US
market
supply
of
potatoes
and
generated
a
combined
total
of
$
1.3
billion
of
revenue.
Washington
State
and
Idaho
applied
an
average
of
11,000
lbs
of
disulfoton
in
2000.
Using
the
worst
case
scenario
for
this
analysis,
an
additional
application
of
methamidophos
could
result
in
an
$
11
increase
in
the
cost
of
chemical
inputs
per
season.
Applying
the
maximum
label
rate
for
imidacloprid
could
increase
grower
costs
approximately
$
45
per
season.
Replacing
disulfoton
with
methamidophos
or
imidacloprid
in
Washington
State
could
result
in
economic
losses
for
the
local
potato
industry
of
approximately
0.3­
1.6%
per
year.
The
Wisconsin
potato
industry
could
potentially
lose
0.5­
2.3
%
as
a
result
of
mitigation.
The
most
severe
impact
of
mitigation
could
occur
in
Idaho,
where
economic
losses
to
the
potato
industry
are
0.7­
2.9
%
per
year,
at
most.
Thus,
the
potential
economic
loss
resulting
from
substituting
either
methamidophos
or
imidacloprid
for
disulfoton
would
appear
to
cause
a
negligible
economic
impact
given
the
potato
industry
 
s
overall
gross
earnings.

Economic
impact
of
mitigation
of
disulfoton
risks
in
radishes
grown
for
seed
3
Economic
data
for
radish
seed
are
scarce
and
information
could
be
found
for
only
635
acres
in
Washington
State.
Based
on
information
from
Washington
state,
break­
even
analysis
shows
that
growers
are
currently
operating
under
very
narrow
profit
margins.
Given
a
$
0.93
break­
even
price
per
pound
of
radish
seed
and
average
prices
for
radish
seed
at
$
0.93
per
lb,
an
increase
in
production
costs
could
negatively
impact
grower
operations
significantly.
Washington
State
University
agricultural
extension
agent
Gary
Pelter
claims
that
without
liquid
disulfoton,
growers
would
have
to
purchase
new
equipment
in
order
to
apply
a
granular
form
of
the
chemical.
The
cost
to
purchase
this
equipment
and
switch
to
a
new
formulation,
Mr.
Pelter
states,
would
be
in
excess
of
$
9,000
per
grower.
He
also
estimates
that
the
cost
of
applying
liquid
fertilizer
separately
would
add
about
$
40
per
acre
to
a
grower
 
s
production
costs.
Therefore,
impact
of
mitigation
could
create
a
severe
economic
burden
to
an
apparently
fragile
radish
seed
industry.

Sources
and
references
Mr.
Michael
Aerts,
Florida
Fruit
and
Vegetable
Association,
Orlando,
FL.

Mr.
Gary
Q.
Pelter,
Washington
State
university
Cooperative
Extension
Service,
Ephrata,
WA.
Dr.
Alan
Schreiber,
Agriculture
Development
Group,
Pasco,
WA.

Dr.
Robert
Stoltz,
University
of
Idaho,
Twin
falls,
Idaho.

Potato
Association
of
America
Handbook
­
Marketing
and
Economics
web
site
at:
www.
css.
orst.
edu/
classes/
CSS322/
marketing.
html
.

USDA
Crop
Profile
for
Potatoes
in
Delaware,
June
2000.

USDA
Crop
Profile
for
Potatoes
in
Idaho,
June
2000.

USDA
Crop
Profile
for
Potatoes
in
Idaho,
June
2000.

USDA
Crop
Profile
for
Potatoes
in
Florida,
December
2000.

USDA
Crop
Profile
for
Potatoes
in
Idaho,
June
2000.

USDA
Crop
Profile
for
Irish
Potatoes
in
North
Carolina,
November
1999.

USDA
Crop
Profile
for
Potatoes
in
Wisconsin,
September
2000.

USDA/
NASS
Agricultural
Statistics
1999,
2000
and
2001.

1997
Enterprise
Budgets:
Carrot
Seed,
Radish
Seed,
and
Onion
Seed;
Columbia
Basin,
Washington.
Gary
Pelter
and
Herbert
Hinman.
Washington
State
University.

USDA/
NASS
Agricultural
Chemical
Usage,
1999
Vegetable
Crop
Summary.

USDA
1997
Census
of
Agriculture;
Volume
1
Geographic
Area
Series;
Part
12:
Idaho.

USDA
1997
Census
of
Agriculture;
Volume
1
Geographic
Area
Series;
Part
47:
Washington.

4
