January 2021 - 21

GRAPES
Michigan State along with trials by other
IR-4 field researchers were instrumental
in EPA registering permethrin for use
on grapes, " he said. " The residue studies
for IR-4 were very extensive. These were
good laboratory practice (GLP) studies
that included large sample sizes. The trials
were performed at universities that have
research farms and extension centers like
Michigan State. "
Increasing need for additional
controls
Permethrin is classified as a Group 3
insecticide, which are sodium channel
inhibitors/modulators.
" Permethrin is an insecticide
with a unique mode of action, " said
VanWoerkom. " This compound does
not degrade as quickly as other Group
3 pyrethroids so it has a lower UVdegradation
rate. A lot of pyrethroids
have a very high degradation rate in the
sun from UV (ultraviolet radiation). This
is important because growers can apply
permethrin and it will last longer than
other Group 3 insecticides. "
Another reason it was important to
gain a U.S. tolerance for permethrin is
the increasing number of invasive pests
entering the United States.
" There are a number of insecticides
registered for use on grapes, but with new
invasive species coming into the country,
we want to keep the number of insecticides
Grape berry moth larvae continue to
be a problem on grapes because of the
development of resistance to labeled
insecticides. Photo: Steve VanTimmeren/
Michigan State University
labeled for use high, " VanWoerkom said.
" New invasive species including the brown
marmorated stink bug, spotted wing
drosophila, and spotted lanternfly are a
threat to small vine climbing fruit crops.
It is important that growers have access to
as many classes of insecticides as possible
to keep the diversity high in order to
prevent resistance. "
" There are also some grape pests that
continue to be a problem because of the
development of resistance. These pests
include the grape leaf hopper, grape berry
moth, and multicolored Asian lady beetle.
These are three major pests on grapes. "
Even with the number of insecticides
registered for use on grapes,
VanWoerkom said growers are facing
stricter restrictions on chemical residues.
" Because of stricter residue restrictions
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growers can't spray as close to harvest
as they used to, " he said. " Also, with
increasing international shipments of
grapes to Europe, the pesticide residue
levels have been reduced even more. This
can make it difficult for growers to keep
residue levels low while maintaining pest
control even though they have numerous
insecticide options. "
Limiting pest damage,
resistance
VanWoerkom said permethrin can be
rotated with other commercial insecticides
in other classes including neonicotinoids
and spinosyns.
" There is interest in biopesticides, but
right now with grapes not so much, " he
said. " There is a very low tolerance for
insect damage on grapes. Growers are
using more conventional insect control
products. There are more biopesticides
becoming available and they are being
used more in rotation with conventional
control products. Smaller farms may
have an opportunity to use some of the
biopesticides, but larger farms are using
more conventional products.
" With proper integrated pest
management and class rotation of
chemicals growers should be able to hold
resistance to a minimum. This is why the
number of chemical classes is so important. "
VanWoerkom said grape growers are
using degree day models to determine
when pests are going to show up on
their crops.
" There are degree day models for all
insect pests on grapes like with other
fruit pests, " he said. " Growers generally
have degree day models based on their
location. In Michigan, a base temperature
of 50˚ F is used for degree-day models
to predict when insects will arrive. It's
accurate almost to the week as to when
insects will show
up. I have been
working with
grape growers
for 13 years
and we have
developed pest
graphs called
trap lines that
we maintain
based on the
insects we trap.
The insects
show up at the
same time and
have the same
emergence
pattern.
" Growers are the best real-world
Grape berry moth
larvae continue to
be a problem on
grapes because of
the development of
resistance to labeled
insecticides. Photo:
Steve VanTimmeren/
Michigan State
University
entomologists and they know when the
insects are going to show up. They know
what the pests look like and how to
control them. "
David Kuack is a freelance technical
writer in Fort Worth, Texas. FGN
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FGN | JANUARY 2021 | 21
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January 2021

Table of Contents for the Digital Edition of January 2021
