HRGSA
BMP Project / Areawide II Handbook
The expectation that mating disruption will provide effective control
under all situations is not realistic. Attention
to detail is required for success with mating disruption programs. This section focuses on the execution of
mating disruption programs and highlights some of the potential pitfalls and
ways to avoid them.
What is
causing the recent increase in codling moth damage?
The trend towards increased codling moth populations and damage we have
been seeing in the last few years have coincided with an increase in the use of
pheromone mating disruption for codling moth control. It would be easy to conclude that there is a
direct cause and effect relationship here.
There are, however, many factors that may be contributing to this
situation. These include:
s
Changing
codling moth phenology
s
Climate
change
s
Increased
abandoned orchards
s
OP
resistant codling moth
s
Poor
execution of mating disruption programs
It should be pointed out that none of the factors
contributing to recent problems with mating disruption is unique to
Why use mating
disruption?
In many areas where mating disruption has been adopted
for codling moth control, this has occurred, not as a stand alone program, but
as one component of codling moth integrated pest management. This trend toward integrating mating
disruption into integrated pest management is being driven by several
factors. Primary among these factors
have been regulatory considerations such as loss of registrations and increased
restricted-entry and pre–harvest intervals for organophosphate and other
pesticides.
Perhaps of equal importance is the stability that mating
disruption brings to the overall program.
In the long run, there is a low likelihood that resistance will develop
to mating disruption. Of more immediate
consequence is that mating disruption does not disrupt natural enemies of
pests. In pear production a very
significant outcome is that by avoiding disruptive codling moth sprays, the
need for post-bloom pear psylla sprays is often eliminated because of increased
biological control.
How does mating
disruption work?
In a non-disruption orchard, the female codling moth
emits a chemical that the male senses, allowing him to locate her and complete
mating. She lays eggs that hatch into
worms. In an orchard that has been
sprayed with a conventional insecticide such as azinphos methyl (Guthion), the
worms contact the spray residue and are killed before entering the fruit. The sprays also have some effect on eggs and
adult codling moths as well.
In a mating disruption block, synthetic pheromone is
applied that creates a blanket of pheromone in the orchard. The conventional wisdom is that the male
cannot find and mate with the female.
Without mating, there would be no fertile eggs, and consequently no
worms to ruin fruit.
This explanation, however, is probably somewhat
simplistic. There is a different picture
emerging about how mating disruption may be affecting the codling moth
population growth rate that is a bit more complex. This is based on research done over the last
several years. It should be emphasized
that this picture is still emerging and not yet complete.
Some research trials have shown that many of the female
moths that are caught in mating disruption orchards are mated. But, in mating disruption orchards the
combined effect of reduced mating, delayed mating, reduced fecundity, and increased
potential for biological control results in a substantial reduction in the codling moth
population and damage. When combined
with supplemental controls, the desired level of control can be achieved.
Codling moth pheromone characteristics
Several characteristics of the pheromone are relevant to
how it should be applied. The pheromone is a volatile compound. When emitted from a pheromone dispenser, it
changes from a liquid to a gaseous form and can move with air currents. The release rate is primarily temperature
driven; warmer temperatures generally result in faster release.
The pheromone is heavier than air.
This means that it will tend to move downward in the atmosphere toward
the ground, and will seek low spots in the orchard.
The pheromone is subject to ultraviolet (UV)
degradation. If raw pheromone is exposed
to sunlight, it will degrade relatively quickly. Regardless of how it is formulated or
dispensed there needs to be some sort of UV protection integrated into the
method. This is particularly relevant to
sprayable formulations of pheromone.
Together, these characteristics mean that the pheromone is
transitory in the orchard. There is some
retention by and reemission from the tree foliage but it is necessary to have a
continuous source of pheromone in the orchard when moths are mating.
Codling moth
mating behavior
There are several factors about codling moth mating
behavior that are relevant to pheromone application. The moths mate in the tree canopy, near the
top of the tree. Females can mate more
than one time; the more times they mate, the more fertile eggs they lay. In the
Success with
mating disruption - grower controlled and block-specific factors
There are several methods for applying pheromone in mating disruption
programs including ties or clips, puffers, true sprayables, and
pheromone-containing fibers. Currently,
the ties and clips are the most common and perhaps the most reliable way to
apply codling moth pheromone. Although
the rest of this section pertains to the use of this type of pheromone
application, most of the principles apply to the others as well.
There are
several factors that are important to the success of just about any mating
disruption program. Grower controlled
factors include:
s
time of pheromone application
s
pheromone placement height
s
pheromone dispenser density
s
pheromone dispenser quality
s
use of supplemental controls
A second group includes factors that are more or less block
specific. That is, they should be
considered on a block-by-block basis.
Careful evaluation of these factors may very likely impact the decisions
you make about the factors listed above.
Block specific factors include:
s
block configuration/border effect
s
gaps in orchard
s
non-uniform canopy
s
prevailing wind
s
topography
s
cultivar
s
codling moth pressure
Each of these factors can be considered in light of what
we know about the mechanism of mating disruption, characteristics of codling
moth pheromone, and mating behavior of codling moth.
Time of pheromone application –
Apply before pear
bloom; apple pink. If the pheromone has
not been applied by the time mating has begun it will not be effective. When used in the
Pheromone placement height –
Place in the top one-third of the canopy.
Not only is this where mating activity of codling moth takes place, but
the pheromone has a tendency to move downward toward the ground.
Pheromone dispenser density – Full
label rate? This is largely dependent on many
of the block specific factors, but much of the work that has demonstrated
success with mating disruption was done at full label rates. It is, however, common to apply the pheromone
dispensers at a rate lower than the full label rate. In general, this practice increases your risk
for failure but may result in satisfactory control if pressure is low. Reducing the rate is usually not advisable
during the first year of implementing a mating disruption program. It is also not advisable on the borders of
orchard blocks where migration from outside the orchard may reduce the
effectiveness of mating disruption.
Pheromone dispenser quality –
Work done by Jay Brunner and Rick Hilton has shown that different dispenser
products have different release rates.
Some dispensers release a greater proportion of their total load early
in the season with less released later on.
Others dispenser products release less product up front. Additionally, some dispensers are not very efficient in
releasing pheromone over the season.
They retain a relatively high proportion of the total pheromone load. Some products also have a high degree of
dispenser-to-dispenser variation in pheromone release.
Use of supplemental
controls – Stand-alone
pheromone may not result in satisfactory control. It is essential to monitor the situation and
evaluate the results based on the total program being implemented. Be prepared to apply supplemental controls if
control is breaking down. Handbook
Section 5 provides a detailed discussion of supplemental control materials.
Block configuration/Borders
Effects – Block configuration
or layout is important because it affects the amount of border in a given block
relative to the orchard interior. This
is illustrated in the diagram below. The
higher the proportion of border to interior area there is in a given block the
higher the risk that mating disruption will fail inside the block. Small blocks have a higher inherent risk
because they consist of greater proportion of border. It is often recommended to increase dispenser
density and/or use supplemental sprays along orchard borders because they are
vulnerable to mated females coming in from outside the orchard.
Gaps in orchard - Both gaps in the orchard due to missing trees and non-uniform
canopy due to uneven tree age or growth will result in discontinuous emission
of pheromone and can effectively create an internal border that may be more
vulnerable to damage.
Prevailing wind - The pheromone is emitted in a gaseous form and moves
with air currents, i.e. wind. In the
Mid-Columbia where wind is a given, this can result in non-uniform distribution
of pheromone in the orchard. One
strategy to deal with this is to load up the upwind side of the orchard (in
Topography - because the
pheromone is heavier than air it will tend to drain off of high spots and
collect in low spots. In an area like
the
Cultivar - Among different
pear cultivars, there are distinct differences in susceptibility to codling
moth damage. For example,
Codling moth pressure – several factors may
contribute to the overall codling moth pressure for a given orchard block. It may seem obvious, but it must be stated
that lack of control in previous seasons will generally carry over and may increase
from one year to the next. Also, close
proximity to bin piles, pulled orchard blocks, and unmanaged trees can all
contribute to higher pressure as moths move out of these areas into adjacent
orchards.
Both internal pressure and external pressure contribute to the overall
level of codling moth pressure for a given block. The response to each may, however, be
different. Generally, in response to
high internal pressure, higher rates of pheromone and supplemental sprays may
be needed over the entire orchard or block.
In response to high external pressure, intensified control may only be
necessary in localized areas such as orchard borders.
Monitoring for codling moth
Orchard monitoring for pest populations or damage is a critical part of
most IPM programs. For codling moth, the
main monitoring technique is trapping with pheromone-baited traps. Traps should be checked weekly. Trap catch results are used in conjunction
with established treatment thresholds to make treatment decisions.
Fruit sampling done at the end of the first codling moth
generation (end-June to early-July) and at harvest can also provide valuable
information. Cullage reports may be
another source of useful information in making decisions about control
practices for the following season.
Important considerations for monitoring in mating
disruption orchards include:
Trap body type - Most traps currently used for codling moth
monitoring in codling moth orchards are delta traps with removable traps
bottoms. This style of trap actually catches
more moths (50% more) than the wing traps when used at the same codling moth
density. So trap type can affect how
catch relates to thresholds.
Lure type
- Pheromone lures come with different amounts of pheromone, and
consequently, will have different levels of attractancy to male moths. This has very important implications for
monitoring programs. Most of the early
work that was done with monitoring in mating disruption blocks was done with
the full rate of dispensers and 10x lures.
One of the challenges in monitoring when using a lower
than full rate of pheromone dispensers is that there is an interaction between
dispenser density and lure strength that affects the attractancy of a
trap. In a non-disruption orchard the
standard 1x lure is sufficiently attractive to males to make them effective for
monitoring. In a mating disruption block
with the pheromone dispensers applied at full rate, the 1x lures are not
effective because they are masked by the pheromone emitted from the
dispensers. The 10x lures are, however,
sufficiently attractive to males to make them effective for monitoring in
mating disruption blocks with a full rate of pheromone dispensers. Conversely, in a non-disruption orchard the
10x lure actually repels male moths. It
seems logical that when monitoring in mating disruption blocks with the
pheromone dispensers applied at half rate that the pheromone load of and
effective lure would be intermediate between 1x and 10x.
Now, there is also a non-pheromone based lure, which is known as the DA
lure, food lure, or kairomone lure. The
attractive compound of this lure is a pear volatile compound. The advantage of this lure is that it is
attractive to both female and male codling moths. Research is being conducted to establish
treatment thresholds for monitoring programs using this lure. Preliminary results indicate that usefulness
of the DA lure in pear orchards will be limited. It may have a better fit for monitoring in
apple and walnut orchards.
Trap placement – Traps need to be in place early, about the time that
pheromone dispensers are put out, located inside and in the upper one-third of
the tree canopy, and at least six feet from the nearest pheromone dispenser to
avoid interference from the pheromone emitted by dispensers.
Trap density and location - The standard density for traps is
one trap per 2.5 to 3 acres. Hot spots,
areas with known high populations, should be monitored separately because
results may not reflect those of the rest of the orchard.
Trap maintenance
- In order to generate consistently reliable information from traps, it
is important to maintain them. It is
necessary to change trap bottoms when they fill up with flies or other insects
or otherwise lose adhesiveness.
Removable trap bottoms make this convenient to do on a regular basis.
It is also necessary to replace the pheromone lure on a
regular interval. This may vary from
Thresholds – Trap catch results are used in conjunction with treatment
thresholds to make treatment decisions.
If catches exceed the threshold, it is likely that damage will result
unless a supplemental treatment is applied.
It should be noted that treatment thresholds in mating disruption
orchards are more conservative than for conventionally managed blocks. Also, note that the treatment threshold for
the second generation is lower than for the first.
Treatment threshold matrix for mating disruption in pears
orchards with pheromone at full label rate and monitoring with 10x pheromone
lure:
|
Codling moth |
|
Cumulative |
|
|
|
generation |
|
trap catch |
|
Action |
|
1st |
|
0 to 5 |
|
treatment not necessary |
|
1st |
|
6 to 10 |
|
|
|
1st |
|
> 10 |
|
treat |
|
|
|
|
|
|
|
2nd |
|
0 to 3 |
|
treatment not necessary |
|
2nd |
|
4 to 5 |
|
|
|
2nd |
|
> 6 |
|
treat |
Impact of unmanaged orchards and backyard trees
One factor that can contribute to
external codling moth pressure and have a severe negative impact on the level
of control achieved in mating disruption orchards is the presence of unmanaged
trees nearby. These may be in an
abandoned or under-managed orchard, in a neighbor’s yard, or located on
unmanaged land. Mated female moths can move into
mating disruption orchards from these areas and wreak havoc.
Hood
River County Ordinance 149 requires that fruit diseases and pests be controlled
on host plants, including fruit trees and non-commercial hosts. If pests are not
controlled, the County may require destruction of the crop and/or trees at the
owner’s expense. The Ordinance is
administered by the Weed and Pest Division of the
If you have any additional questions or are interested in more
information about implementing mating disruption, contact Steve Castagnoli at
OSU Extension Service (541) 386-3343.