January
6,
2005
Ms.
Debbie
Edwards
Director,
Reregistration
Division
Environmental
Protection
Division
1101.
A
USEPA
Headquarters
Ariel
Rios
Building
1200
Pennsylvania,
NW
Washington,
D.
C.
20460
Dear
Debbie:

The
NPC
has
previously
supplied
input
on
the
critical
role
of
Guthion
in
the
U.
S.
potato
industry.
Recent
developments
in
the
potato
industry
have
only
added
to
the
importance
of
this
product
to
growers.
This
document
includes
previously
submitted
information
and
new
material
on
the
product.
The
NPC
believes
that
Guthion
should
be
continued
for
use
on
potatoes
where
it
serves
as
an
important
IPM
tool,
particularly
where
the
use
of
alternatives
can
trigger
problems
with
other
pests
such
as
mites.
The
need
for
Guthion
has
taken
on
new
urgency
with
the
outbreak
of
a
devastating
insect
pest
of
potatoes
in
the
Pacific
Northwest,
the
potato
tuberworm.

Guthion
has
a
long
history
of
use
on
potatoes
and,
at
one
time,
was
one
of
the
most
widely
used
insecticides
on
the
crop
and
is
almost
exclusively
used
for
control
of
the
Colorado
potato
beetle.
In
the
near
term,
the
development
of
resistance
of
the
target
pest
to
the
insecticide
and
also
the
registration
of
alternative
products,
the
use
of
Guthion
declined
in
many
regions.
However,
due
to
the
combination
of
the
product's
low
cost,
high
effectiveness,
non­
flaring
of
mites,
and
its
value
for
resistance
management,
the
use
of
Guthion
on
potatoes
in
the
Columbia
Basin
has
increased.
In
2001,
Guthion
was
applied
to
approximately
26,000
acres
in
Washington,
with
a
smaller
amount
used
in
Oregon,
making
it
one
of
the
most
important
insecticides
for
foliar
applications
against
CPB
in
the
region.
In
2003,
the
state
with
the
greatest
use
was
Wisconsin
with
26%
of
acres
treated
an
average
of
two
times.
These
estimates
are
based
on
USDA
NASS
statistics
for
2004.
Other
states
expect
to
increase
their
reliance
on
Guthion
in
the
near
future,
assuming
the
product
remains
available.
These
states
include
Colorado,
Oregon,
and
North
Dakota.

Resistance.
CPB
resistance
to
Guthion
is
often
mentioned
as
one
of
the
reasons
for
the
reduced
benefits
associated
with
Guthion.
It
is
important
to
remember
that
states
which
represent
approximately
two­
thirds
of
potato
production
do
not
have
Guthion
resistant
CPB.
Also,
these
states
and
states
with
resistant
CPB
have
other
pests
for
which
Guthion
can
be
used.
Development
of
resistance
by
the
CPB
is
an
important
concern
to
Columbia
Basin
potato
growers.
Growers
are
applying
different
classes
of
insecticides
to
prevent
or
delay
the
onset
of
resistance
in
CPB.
CPB
is
thought
to
have
already
developed
resistance
to
pyrethroid
Ms.
Debbie
Edwards
January
6,
2005
Page
2
insecticides
in
Idaho.
Now
that
resistance
to
neonicotinoid
insecticides
in
the
Mid
West
and
Eastern
United
States
has
been
widely
documented,
it
is
expected
that
growers
will
increase
their
reliance
on
Guthion.
Due
to
resistance
issues
alone,
the
retention
of
Guthion
is
very
important
to
potato
growers.
As
neonicotinoid
resistance
spreads,
reliance
on
Guthion
is
expected
to
increase
further.

Integrated
Pest
Management.
In
addition
to
CPB
resistance
issues,
the
Columbia
Basin
of
Washington
and
Oregon
has
a
second
unique
feature
which
warrants
retention
of
Guthion.
It
is
the
only
location
in
North
America
that
mites
(
two­
spotted
spider
mite)
are
a
routine
pest
of
the
potato.
On
average,
about
20
to
25%
of
potato
acres
in
this
region
are
treated
for
mites.
It
is
unclear
why
mites
are
such
a
severe
pest
of
potatoes
only
in
the
Columbia
Basin.
Research
by
Dr.
Alan
Schreiber
(
Washington)
and
Dr.
Gary
Reed
(
Oregon)
has
demonstrated
that
applications
of
pyrethroid
insecticides
for
CPB
control
can
cause
mite
outbreaks.
Mite
outbreaks
also
occur
in
fields
that
are
not
subjected
to
pyrethroid
insecticide
applications.
Guthion
does
not
share
this
characteristic
with
the
pyrethroid
insecticides.

Growers
can
apply
Guthion
for
control
of
the
first
and
second
generations
of
CPB
and
not
have
a
mite
outbreak
that
would
then
require
an
application
of
a
miticide.
Use
of
Guthion
for
CPB
control
to
avoid
a
mite
outbreak
is
considered
to
be
a
critical
potato
IPM
tactic
in
the
Columbia
Basin.

Cost.
Guthion
is
approximately
equal
in
cost
to
the
lowest
cost
alternatives
on
the
market,
the
pyrethroid
insecticides.
However,
application
of
pyrethroid
insecticides
in
some
situations,
as
mentioned
above,
can
result
in
mite
outbreaks.
In
this
case,
the
cost
of
application
of
a
pyrethroid
insecticide
and
the
resulting
application
of
a
miticide
is
very
expensive
in
comparison
to
the
single
application
of
Guthion.

Effectiveness.
Guthion
is
well
known
to
be
a
very
effective
material
for
control
of
CPB
in
areas
where
resistance
to
the
product
does
not
occur.

Potato
Tuberworm.
The
Columbia
Basin
of
Washington
and
Oregon
has
recently
suffered
from
a
severe
outbreak
of
potato
tuberworm.
Historically,
this
pest
has
been
a
tropical/
subtropical
pest
and
has
not
been
a
problem
at
this
latitude
in
either
the
Northern
or
Southern
Hemispheres.
Apparently,
this
pest
has
mutated
and
adapted
to
this
climatic
region
as
it
has
successfully
overwintered
during
the
2003­
2004
winter,
which
was
expected
to
wipe
out
the
population.
Potato
tuberworm
can
be
a
production­
ending
pest
of
potatoes.
Complete
control
of
this
new
pest
is
essential
to
the
continued
production
of
potatoes
in
Washington
and
Oregon.

In
California,
where
tuberworm
has
been
the
most
serious
pest
of
potatoes
for
decades,
the
standard
insecticide
for
control
of
the
pest
was
Guthion.
There
is
ample
anecdotal
and
published
data
that
Guthion
is
an
effective
means
for
controlling
potato
tuberworm.
Guthion
will
likely
be
a
primary
recommended
product
for
control
of
potato
tuberworm
in
the
Columbia
Basin.
Ms.
Debbie
Edwards
January
6,
2005
Page
3
Conclusion.
The
NPC
supports
the
continued
registration
for
Guthion
on
potatoes
for
the
U.
S.
This
request
is
based
due
to
the
development
of
resistance
in
key
alternatives,
its
role
in
IPM
and
resistance
management
programs,
the
product's
significant
cost­
effectiveness,
and
for
management
of
a
devastating
new
insect
pest,
the
potato
tuberworm.

Sincerely,

John
Keeling
Executive
Vice
President/
CEO
WDC99
1025274­
1.027357.0010
