Codling Moth
Insecticide Resistance Management
James F. Walgenbach,
Extension Entomologist, NCSU/Entomology
Insecticide resistance management refers
to using pest management practices that
prevent or delay the development of resistance
by an insect population. In the past
two years there has been an increased
incidence of codling moth resistance
to a diversity of insecticides. With
the recent registration of two new insecticides
for codling moth control (Delegate and
Altacor), now is the time to implement
insecticide resistance management to
preserve the long-term utility of these
new products.
Insecticide resistance management practices
revolve around the concept of minimizing
exposure of an insect population to insecticides,
because the less often a population is
exposed to a chemical the lower the selection
pressure for resistance to develop. Unfortunately,
insecticides are an essential component
to insect control in apples, and it is
not practical to eliminate their use.
However, there are alternative management
options that can be used to help suppress,
and in some instances control, codling
moth populations so that fewer insecticide
applications are required to achieve
the required level of control.
Alternative Management Options
Mating Disruption. The use of
pheromone-mediated mating disruption
is gaining more popularity around the
world for management of codling moth,
and there is a dramatic increase in use
in NC this year. While mating disruption
is an effective strategy for controlling
low population densities of codling moth,
by itself it cannot be relied upon to
control high populations. However, mating
disruption does help to suppress damage
by high populations, and superior levels
of control can achieved when mating disruption
and insecticides are used in combination.
After several years of using mating disruption,
population densities can be lowered to
the point where the number of insecticide
applications targeting codling moth is
reduced. In areas where mating disruption
has been used continuously for multiple
years, growers have observed a more stable
low level population density and do not
experience large year-to-year fluctuations.
In order to monitor the success of mating
disruption over time, it is essential
that moth populations are monitored with
pheromone traps. There is no substitute
for monitoring to determine population
density and the need for supplement applications
of insecticides. Because codling moth
densities can vary considerable from
one area of an orchard to another, and
because the effective area of a trap
is about 3 acres, ideally one trap should
be used for every 3 acres of orchard,
with one trap per 4 to 5 acres being
the minimum. Finally, traps should be
placed in this portion of trees where
moth activity is greatest.
Codling
Moth Virus. Commercial
formulations of a naturally occurring
virus of the codling moth (Cydia
pomonella granulovirus) are now
available and have been used with good
results in both small and large plot
trials in North Carolina. Cyd-X (1-3
oz per acre) and Carpovirusine (6 to
13 oz per acre) are two commercial products
that contain the same virus. Virus particles
are broken down by UV light, so the residual
activity of these products is only about
7 days. In addition, because the virus
must be ingested by larvae and death
does not occur until at least 3 days
later, under higher population densities
there is likely to be stings on apples
(small holes where the larva began feeding),
but larvae will die before tunneling
into fruit. Use of the codling moth virus
is similar to inflicting a disease on
the population, and represents an alternative
mode of action completely different from
any chemical insecticide. Incorporating
these products into your spray program
when codling moth egg hatch is occurring
is another option for reducing exposure
of populations to insecticides, and thus
minimizing resistance development.
Insecticide Use Patterns
Although the goal of a codling moth
insecticide resistance management program
is to minimize insecticide use, insecticides
are an essential component to controlling
this insect, and under high population
densities multiple applications per generation
are necessary. Three rules to following
when using insecticides are:
Application
Timing. Poor control
failure is often times associated with
mistiming an application. This is particularly
important with many of the new insecticides
that have narrow spectrum of pest activity
and that are most effective against eggs
or larvae.
Dosage. Exposing an insect population
to a sublethal dose, or a does not kill
a high percentage of individuals, greatly
accelerates the rate of resistance development.
Insecticides should not be applied at
rates below those listed on the label.
Rotation. For those insects that
complete two or more generations per
year, it is important that insecticides
with different modes of action are used
against different generations. For instance,
if Intrepid, Rimon, and/or Delegate are
used against the first generation in
May and June, do not apply any of these
materials during the second generation
in July and August. Hence, decisions
should be made at the beginning of the
year as to which insecticide(s) will
be used against the first and second
codling moth generations.
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