1
UNITED
STATES
ENVIRONMENTAL
PROTECTION
AGENCY
WASHINGTON,
D.
C.
20460
OFFICE
OF
PREVENTION,
PESTICIDES
AND
TOXIC
SUBSTANCES
Memorandum
SUBJECT:
Asparagus
Benefits
Assessment
for
Disulfoton
FROM:
Nikhil
Mallampalli,
Ph.
D,
Entomologist
Herbicide
and
Insecticide
Branch
Colwell
Cook,
Ph.
D,
Entomologist
Herbicide
and
Insecticide
Branch
Anthony
Gilbert,
Economist
Economic
Analysis
Branch
Biological
and
Economic
Analysis
Division
(7503C)

THROUGH:
David
Brassard,
Ph.
D.,
Senior
Scientist
Arnet
Jones,
Ph.
D.,
Branch
Chief
Herbicide
and
Insecticide
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)

PRP
review
date:
September
5,
2001
Summary
of
Analysis
Disulfoton
is
a
critical
pest
management
tool
for
asparagus
growers
in
the
primary
production
regions
of
the
country.
These
regions
lie
in
the
Pacific
northwest
and
California,
and
face
large
economic
losses
if
populations
of
the
European
asparagus
aphid
are
not
rigorously
and
immediately
controlled.
Management
of
this
insect
pest
is
the
primary
reason
for
disulfoton
use
in
this
crop.
Human
health
risk
modeling
suggests
that
the
liquid
form
of
disulfoton
may
pose
risks
to
mixers,
loaders,
and
applicators.
However,
all
the
disulfoton
used
in
the
U.
S.
asparagus
crop
is
applied
in
liquid
form,
either
aerially
or
by
ground
spray
rigs.
Thus,
eliminating
these
methods
of
application
is
likely
to
result
in
significant
negative
impacts
on
asparagus
production
in
the
western
U.
S.
The
following
analysis
provides
an
overview
of
U.
S.
asparagus
production,
the
role
of
disulfoton
in
asparagus
production,
a
description
of
2
available
alternatives
to
disulfoton,
and
estimates
of
the
impacts
of
eliminating
aerial
application
and/
or
the
liquid
forms
of
disulfoton
in
this
crop.
Overview
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.
HED
risk
modeling
indicates
that
the
liquid
form
of
this
chemical
may
pose
hazards
to
mixer/
loaders
and
applicators
(calculated
MOE
=
1­
35)
in
asparagus.
Therefore,
SRRD
has
asked
BEAD
to
investigate
the
importance
of
liquid
disulfoton
in
U.
S.
asparagus
production
and
the
impacts
created
by
restrictions
on
using
the
liquid
form
of
this
chemical.
Re­
entry
and
pre­
harvest
intervals
are
not
being
considered
for
regulatory
action
at
this
time.

Asparagus,
Asparagus
officinalis,
is
a
perennial
row
crop
grown
primarily
in
Washington
and
California,
which
together
account
for
about
83%
of
U.
S.
production
of
this
vegetable.
Michigan
accounts
for
approximately
13%,
while
the
rest
of
the
crop
is
grown
in
Arizona,
Idaho,
Illinois,
Maryland,
Minnesota,
New
Jersey,
and
Oregon
(7)
.
Asparagus
requires
well­
drained,
heavier
soil
with
a
relatively
alkaline
pH,
and
does
best
in
climates
where
periods
of
either
cold
or
drought
regularly
occur.
These
periods
stimulate
dormancy
in
the
plants,
and
this
in
turn
subsequently
produces
more
vigorous
vegetative
growth
of
the
plants,
and
thus
higher
yields.
These
conditions
are
best
provided
in
the
midwestern
and
northwestern
parts
of
the
U.
S.
A
total
of
approximately
76,000
acres
of
asparagus
were
grown
in
the
U.
S.
in
1999
(7)
.
While
asparagus
can
be
planted
either
with
seeds,
transplants,
or
crowns,
the
most
common
method
is
to
establish
fields
is
to
plant
one­
year
old
crowns.
Crops
are
harvested
no
earlier
than
the
second
year
after
planting,
so
as
to
allow
plants
to
undergo
more
vigorous
growth.
Harvesting
of
asparagus
spears
generally
begins
in
mid­
January
in
the
western
U.
S.
and
in
early
spring
in
the
mid­
west
and
east
coast
areas,
and
continues
through
June.
Virtually
all
harvesting
is
done
by
hand,
on
a
repetitive
basis,
every
one
to
five
days
during
the
early
part
of
each
growing
season.
This
harvesting
activity
lasts
one
to
two
months,
depending
on
the
size
and
productivity
of
fields.
After
harvest,
remaining
spears
are
allowed
to
grow
out
into
"ferns"
(vegetative
growth),
during
which
little
to
no
human
presence
is
required
in
fields
(1,
6)
.

Pest
insect
biology
In
asparagus,
disulfoton
is
used
primarily
to
control
the
European
asparagus
aphid,
Brachycorynella
(
=
Brachycolus)
asparagi,
an
insect
specialized
to
feed
only
on
this
plant.
B.
asparagi
was
accidentally
introduced
from
Europe
in
the
early
1920s
and
is
a
serious
pest
of
this
crop
in
Washington,
Oregon
and
California
(1,
6)
.
It
is
brought
into
fields
primarily
via
infested
crown
brought
in
from
nurseries.
Once
in
fields,
aphids
overwinter
as
eggs
in
old
fern
debris
and
cracks
in
the
soil.
All
life
stages
occur
on
edible
varieties
of
asparagus.
Eggs
hatch
in
the
spring
and
nymphs
crawl
onto
asparagus
spears
as
they
emerge
from
the
soil.
During
most
of
the
crop's
growing
season,
aphids
exist
as
nymphs,
feeding
and
reproducing
asexually.
Aphid
populations
tend
to
build
up
under
conditions
of
low
rainfall
or
humidity.
Major
damage
to
plants
occurs
from
a
toxin
injected
by
aphids
during
feeding.
This
toxin
causes
bushy,
stunted,
and
bluish­
green
growth.
This
in
turn
reduces
the
number
of
viable
spears,
due
to
dessication
of
the
developing
crowns.
The
toxin
itself
can
also
cause
a
delay
in
bud
break
and
a
profusion
of
small,
less
valuable
spears
(1,
6)
.
Even
low
populations
of
this
aphid
can
cause
total
losses
in
an
asparagus
field,
and
growers
often
have
no
choice
but
to
plow
out
the
field
and
plant
again
(1,
4,
5)
.
Other
aphid
species,
including
the
green
peach
aphid,
and
the
bean,
melon,
and
potato
aphids,
can
also
become
problems
on
asparagus
if
left
uncontrolled,
but
disulfoton
use
is
thought
to
keep
these
pests
rare
(1,
3)
.
3
Role
of
disulfoton
in
asparagus
production
During
1987­
1998,
a
weighted
average
of
37,000
lb
of
disulfoton
(active
ingredient)
were
applied
on
asparagus
nationwide;
of
this
96
%
was
used
in
California
and
Washington.
The
granular
form
of
disulfoton
is
currently
not
registered
for
use
on
asparagus,
(10)
so
all
of
these
applications
may
reasonably
be
considered
to
be
of
the
liquid
form.
Virtually
all
of
this
use
was
targeted
against
the
asparagus
aphid
(1,
3,
4)
.

In
California,
Washington,
and
Oregon,
disulfoton
is
applied
using
both
ground­
boom
or
aerial
methods.
However,
in
all
these
regions,
aerial
applications
are
by
far
the
more
common.
In
1999,
65
%
of
applications
in
California
were
aerial
(2)
.
In
California,
closed
mixing/
loading
systems
are
required,
but
this
is
not
the
case
in
other
states
where
disulfoton
is
registered
for
use
on
asparagus.
In
Washington
and
Oregon,
an
estimated
98
%
of
applications
are
aerial
(3)
.
As
a
result,
most
of
the
disulfoton
use
in
these
primary
asparagus
producing
areas
is
in
the
liquid
form.
The
chemical
is
applied
1­
2
times
per
year,
almost
always
during
the
"fern"
stage,
when
virtually
no
human
presence
in
fields
is
required.
Aerial
application
is
dictated
by
the
mat­
like
growth
of
asparagus
in
the
fern
stage,
which
must
be
optimized
to
ensure
good
harvests
the
following
season,
and
by
the
need
to
keep
the
crop
well
irrigated,
which
makes
the
soil
wet
and
unstable.
These
factors
often
make
the
use
of
ground
application
equipment
impossible,
due
to
the
difficulty
involved
in
moving
it
about
and
the
risk
of
significantly
damaging
ferns
(3,
4)
.

Asparagus
farm
sizes
tend
to
be
larger
in
California
as
compared
to
other
regions
of
the
western
U.
S.
production
areas.
In
1997,
48
%
of
asparagus
farms
in
California
had
100
acres
or
more
of
the
crop;
on
average,
these
farms
had
431
acres
grown.
Overall
average
farm
size
was
219
acres
(8)
.
In
Washington,
no
farms
are
greater
than
300
acres;
average
size
was
62
acres
(
9)
.
The
maximum
area
treated
in
a
day
by
an
aerial
applicator
has
been
estimated
to
be
about
75
to
150
acres
in
Washington,
and
150
to
200
acres
in
California
(3,
4)
.
These
estimates
were
based
(by
the
crop
experts
contacted)
on
discussions
with
aerial
applicators
in
their
respective
states.
This
is
partly
a
result
of
the
fact
that,
even
on
larger
farms,
asparagus
fields
are
interspersed
with
other
crops,
and
applicators
do
not
typically
treat
all
the
acreage
of
a
given
grower
at
any
one
time
(3,
4)
.

Chemical
alternatives
For
aphid
control
in
asparagus,
chlorpyrifos
is
the
only
currently
registered
chemical
control
alternative
available
in
California.
It
is
also
available
in
Washington,
and
Oregon,
where
dimethoate
is
also
an
option
in
this
context.
Both
these
insecticides
have
significant
drawbacks
in
this
cropping
system,
however.
Chlorpyrifos
is
not
as
effective
as
disulfoton
in
eliminating
asparagus
aphids
from
fields
due
to
a
short
residual
effect,
and
may
cause
outbreaks
of
other
aphid
species
(1,
3)
.
Dimethoate
also
has
a
very
short
residual
effect
(1
day)
and
thus
is
also
not
as
good
as
disulfoton
(3)
.
Biological
control
agents
such
as
ladybeetles
and
parasitic
wasps
occur,
but
cannot
usually
keep
up
with
aphid
infestations
in
the
western
growing
regions
(3,
4)
.

Impact
of
restricting
disulfoton
use
in
asparagus
Curtailing
aerial
or
liquid
application
of
disulfoton
will
be
effectively
equivalent
to
eliminating
this
pesticide
in
asparagus,
since
ground
application
is
so
difficult
and
the
granular
form
is
not
an
option
4
for
control
of
the
target
pest.
Given
the
damage
inflicted
by
the
asparagus
aphid,
this
can
be
expected
to
result
in
substantial
economic
losses
to
growers
in
Washington
and
California.
Yearly
per
acre
economic
losses
in
Washington
could
exceed
$700
if
disulfoton
were
eliminated
and
growers
were
forced
to
rely
on
the
other
available
chemical
alternatives
(chlorpyrifos
and
dimethoate).
This
would
translate
into
aggregate
losses
to
asparagus
growers
of
about
$273,000
per
year.
In
California,
per
acre
economic
losses
could
exceed
$1000
per
season
with
an
aggregate
loss
to
growers
of
approximately
$166,000
per
year.
This
analysis
corroborates
the
results
of
an
earlier
study,
conducted
by
Washington
State
University
in
1997.
It
estimated
aggregate
losses
to
the
asparagus
industry
in
these
states
of
about
$38,000,000
per
year,
about
40%
of
gross
farm­
level
(preprocessing
level)
revenue
(1)
.
That
study
was
based
on
chlorpyrifos
and
malathion
as
the
chemical
alternatives
available.
The
authors
estimated
that
this
would
end
west
coast
asparagus
production
in
four
years
at
most.

Sources
and
References
1.
Eskelson,
S.,
A.
Schreiber,
S.
E.
Crawford,
and
R.
J.
Folwell.
1997.
Biological
and
Economic
Assessment
of
the
Impact
of
Pesticide
Use
on
Asparagus.
Washington
State
University
Publication
No.
MISCO193.

2.
California
Dept
of
Pesticide
Regulation
data,
courtesy
of
Linda
Herbst,
University
of
California,
Davis.

3.
Dr.
Alan
Schreiber,
Agriculture
Development
Group,
Pasco,
WA.

4.
Dr.
Robert
Mullen,
University
of
California
Cooperative
Extension
Service,
Stockton,
CA.

5.
Ms.
Cherie
Watte,
California
Asparagus
Commission,
Stockton,
CA.

6.
USDA
Crop
Profile
for
Asparagus
in
California,
Feb.
2000.

7.
USDA/
NASS
Agricultural
Statistics
2000.

8.
USDA/
NASS
Census
of
Agriculture,
California
State
and
County
Data.
1997.
Vol.
1,
part
5.

9.
USDA/
NASS
Census
of
Agriculture,
Washington
State
and
County
Data.
1997.
Vol.
1,
part
47.

10.
Crop
Data
Management
Systems
Pesticide
database,
http://
www.
cdms.
net/.
