What is IPM?
Integrated pest
management (IPM) is a philosophy of pest control founded on the
principles of ecology. In practice, it involves using several control
tactics based on a knowledge of the crop, pests and associated natural
enemies to avoid crop loss and minimize harmful effects on the
environment. Implementing IPM requires an understanding not only of
insect and mite biology and ecology but also of the entire orchard
system. This includes the plants and animals that comprise the orchard
community, as well as consideration of contributions from the
surrounding habitat. The orchard system also takes into account
financial, physical and human aspects of orchard operations.
IPM
requires a more tolerant approach to pest control than traditional
insecticide-based programs. Eliminating all insects and mites from the
orchard is not the objective of IPM. Natural enemies are to be conserved
as much as possible and some damage, especially to foliage, is
tolerated. For example, pests that attack the foliage can usually be
allowed to build to levels higher than those that attack the fruit.
There
are both positive and negative impacts associated with the reduced
insecticide use that usually accompanies the adoption of an IPM
approach. Benefits of IPM include greater survival of natural enemies,
slower development of resistance, less pest resurgence, fewer outbreaks
of secondary pests, less negative impact on the environment, and greater
worker safety. On the negative side, potential pests that are
coincidentally controlled by insecticides used to control key pests may
be released from all but natural controls. Natural controls will be
effective for some. For others, however, the release from insecticidal
control will result in population levels that are sometimes damaging.
The transition to more intensive IPM programs in orchards will require
knowledge and patience-knowledge of pest and natural enemy biology and
patience to allow natural enemy build-up. Selective controls will have
to be used for pests that are not maintained at acceptable levels by
natural controls.
An IPM program involves:
- Identifying pests, which requires knowledge of their biology and the damage they inflict.
- Identifying the natural enemies of pests.
- Understanding the biological and environmental factors that affect the abundance and distribution of pests and natural enemies.
- Monitoring both pests and natural enemies to determine potential for damage and biological control.
- Tolerating higher levels of pests, particularly foliage feeders.
- Using a treatment threshold to decide when control is needed.
- Knowing the efficacy of available control tactics, as well as their potential impact on non-target pests and natural enemies.
- Building flexibility into the control program to allow for variations from block to block or year to year.
- Follow-up to see how well control measures work and if further action is needed.
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History
The
advent of synthetic insecticides after World War II launched a new era
of pest control. The number of registered pesticides rose from about 30
in 1936 to more than 900 in 1972. The new chemicals were effective, easy
to use and inexpensive. For several years it appeared that
broad-spectrum pesticides could eliminate most pest problems. Sprays
were often used on a routine, preventive basis, providing protection for
the crop whether the insect was there in damaging numbers or not.
Soon,
however, insects began to develop resistance to insecticides, and new
problems arose because natural enemies were eliminated. Some insects
that previous to broad-spectrum insecticides had been kept in check by
their natural enemies now reached pest status. In the absence of natural
enemies, growers often applied more toxic products in an effort to
control these secondary pests, as well as resurging populations of the
insecticide-resistant target pest. Orchardists became trapped in a cycle
of using more insecticides to cure one pest problem, which resulted in
the worsening of another pest problem. The cost of control increased
while the degree of control often declined and the harmful effect on the
environment escalated.
The inability to control mites during the
1950s and 1960s was a major impetus in the development of integrated
mite control in apple orchards. Mites were quickly developing resistance
to miticides. Scientists found that predatory mites had developed
resistance to some organophosphate insecticides and, if these were used
at selective rates and properly timed, biological control of mites could
be integrated with chemical control of other insects. It meant
tolerating some mites in the orchard until predators gained control and
at first was a difficult concept for growers to accept. But integrated
mite control became so successful that many orchardists in the Pacific
Northwest have not had to apply chemicals to control mites since the
1960s.
Although integrated mite management was widely adopted in
the early 1970s, growers have continued to rely almost exclusively on
insecticides for control of other pests. Insecticides have been
effective and in the absence of any crisis, as was experienced with
mites, IPM was a less attractive alternative. Recently, however, the
pace toward widespread implementation of IPM for the entire complement
of orchard pests has been quickening. A number of factors are
responsible for the renewed interest in IPM. Those most evident are:
- A decline in the number of insecticides available because of the EPA's re-registration of old pesticides;
- A lack of new registrations because of development costs and regulatory requirements; and
- reduction in the effectiveness of registered products because of pest resistance.
The
public's concern over insecticide residues on food, contamination of
the environment, and exposure of farm workers to insecticide residues
during thinning, tree training, and harvesting operations are issues of
increasing importance. IPM addresses each of these concerns. Moreover,
IPM has the capacity to evolve to accommodate new pests and control
techniques.
Integrating Management Tactics
A
successful IPM program incorporates a variety of compatible tactics
such as biological control, cultural control, judicious use of
insecticides, and autocidal techniques such as mating disruption. It
does not preclude the use of insecticides but attempts to use them as a
last line of defense against pests, not as the first option for control.
IPM recognizes that insecticides are one of many tools available for
managing pests and the more tools that are included in a management
program, the stronger it will be.
For example, where mating
disruption is used to control codling moth, supplemental treatment with
insecticides may be needed to reduce pest pressure on orchard borders to
prevent damage resulting from mated moths immigrating from adjacent
sources.
Conflicts often arise when attempting to integrate
insecticidal and biological controls. However, these problems can be
reduced by using insecticides that are selective, that is, those that
control the pest but are less toxic to natural enemies. Applying
insecticides only where needed and timing applications when the pest is
most vulnerable will maximize benefits of the chemical control while
reducing the impact on natural enemies. Delaying treatments as long as
possible to allow predator and parasitoid populations to build up or
using chemical controls during the dormant period before natural enemies
are active are strategies that will help to encourage biological
controls.
In an IPM program, pests are not treated in isolation.
It is important to consider their relationships with other insects and
with their environment. The distribution and abundance of pests are
influenced by their natural enemies, weather, orchard practices
including pruning, fertilization and cover crop management, and by
habitats surrounding the orchard that may provide alternate hosts for
pests and their natural enemies. Understanding that these factors
influence pest populations is a key to successful pest management.
Similarly,
decisions that affect the biological components of the orchard system
are not made without considering the larger social system of which they
are a part. The tree fruit industry is well aware of how pesticide laws
and the concerns of consumers can dramatically impact production and
marketing programs. IPM should provide the platform for developing a
more harmonious relationship between the agricultural community and
social and environmental action groups.
Components of an IPM programPest identification
The
use of broad-spectrum insecticides reduces the need to know
specifically what pest is causing what damage. Treatment decisions are
often prevention-based, and several target pests are killed with the
same treatment. As more selective controls are incorporated into a
management program, it becomes increasingly important to know more about
the target pest in order to achieve control. The effectiveness of
selective controls often depends on very accurate timing of
applications.
Damage in an orchard may not necessarily be due to
the most abundant insect present at the time observations are made. An
incorrect diagnosis can lead to unnecessary sprays. Many insects found
in the orchard are not pests, but only incidental visitors, while others
are beneficial, acting as biological controls for pests. Some pest and
beneficial species look similar. For example, many stink bugs are
potential pests, but a
Brochymena species is predaceous and a natural enemy of soft-bodied pests in orchards.
Several
kinds of information are helpful when identifying an insect in the
field. Physical appearance (including color, size and shape) is usually
of primary importance. However, since many pests restrict their feeding
to only certain plant parts, knowing where they are most likely to be
found helps narrow the possibilities when making field identifications.
Similarly, many insects leave characteristic feeding damage that
provides a clue to their identity. Descriptions and pictures of the most
common insect and mite pests, their natural enemies, and typical damage
caused by pests are presented in this manual.
Monitoring
Monitoring
is the most fundamental yet the most often neglected activity in an IPM
program. Both the need for control and the effectiveness of any action
taken are determined by monitoring pest and natural enemy populations.
Since it is impossible to count all the insects, only a portion, a
sample, is counted. Information obtained from the sample is used to make
inferences about an insect's density in the entire orchard. To decide
if a control is required, pest density must be related to the potential
damage and balanced against how likely it is that the pest's natural
enemies will be able to keep it below damaging levels. Even if treatment
thresholds are unknown, sampling provides information on the insect's
stage of development, population densities and the ratio of pests to
natural enemies, all of which form a sound basis for decision making.
Management in the absence of sampling usually leads to an overuse of
insecticides. It is important to know how a pest develops, i.e., its
life history, because different life stages may be monitored and managed
in different ways. For example, you would sample foliage to look for
leafroller larvae, which feed on leaves and fruit, but use pheromone
traps to monitor adults. Control decisions may be based on either of
these monitoring methods at different times during the season (see
Leafrollers, Direct Pests).
Different sampling methods are used, depending on the type of pest and
monitoring objective. Since all methods only estimate the number of
individuals in the actual population, there is always variation from one
sample to the next. This variation is kept within acceptable limits by
guidelines that specify how, when, and where to sample. Detailed
sampling guidelines for many orchard pests are presented in this manual.
Some general methods of monitoring orchard pests and their natural
enemies are outlined here.
Visual counts Caterpillars,
leafminers, leafhoppers, aphids, mites and many of their natural enemies
can be sampled simply by counting them on leaves, shoots or fruit. A
10-power hand lens is an essential tool. It makes sampling smaller
insects easier and is necessary when evaluating parasitism of
leafminers.
Leaf brushing Leaf brushing is the standard
method for counting mites and can be used to estimate psylla densities.
A machine is used to brush mites or immature pear psylla off leaves and
onto a glass plate placed over a grid (Appendix 4) to make counting
easier. See the appropriate pest section for the kind and number of
leaves to be sampled and subsequently brushed.
IPMF3
Beating tray
Insects such as adult pear psylla, plant bugs, older caterpillars, and
predators of pear psylla and aphids can be monitored by jarring them
from limbs onto a cloth tray. A white cloth provides a good background
for counting most insects. However, light colored pests such as
campylomma are more easily detected against a black cloth. The tray is
held under an almost horizontal section of limb that is 3/4 inch to
1-1/2 inches in diameter with an average complement of branches and
spurs. The limb is firmly tapped three times with a l-foot length of
stiff rubber hose. Old spray hose works well. Insects jarred from the
tree cling to the cloth and can easily be counted. Insects and debris
are removed from the tray by turning it upright and tapping it lightly
with the hose.
Beating tray counts should be taken at random
throughout a block. The number of tray samples required to make a
management decision varies and is discussed in the specific pest
sections. When sampling for parasitic wasps or other minute insects, an
aspirator can be used to collect the specimens for later identification.
Traps Pheromone traps
are a quick and convenient way to monitor many moth species, San Jose
scale and campylomma. When used in conjunction with phenology models,
they enable growers to apply controls at precise times in an insect's
life history rather than according to a calendar-based schedule.
Pheromones are volatile chemical attractants produced by insects to
communicate with their own species. Most pheromones used in traps are
synthetic compounds that mimic those released by females to attract
males for mating (see section on Mating Disruption and Degree-day Models
in Part I). The main limitation of pheromone traps is that only the
adult males can be monitored, and activity of males may not always be
representative of female activity. Pheromone traps can be used to help:
CM_f8
- monitor when adult flight begins (biofix), as well as peak flight and its duration;
- track seasonal development;
- determine when populations reach treatment thresholds;
- assess how well control programs are working;
- synchronize degree-day models with actual pest development;
- monitor the presence of exotic or introduced pests.
Traps
of various designs and sizes are available commercially. Some are
cylinder shaped, while others are referred to as wing or tent types.
Most are made of cardboard and have an adhesive on the inside (Figure
29). A lure containing the pheromone is placed inside the trap.
Pheromone is slowly released and insects are attracted to and caught in
the trap's adhesive surface. The number of insects that can be caught in
a trap depends on the size of the sticky surface.
Choosing a trap system:
The size and shape of the trap can make a difference in how efficiently
it catches the target insect. The trap should be easy to assemble and
efficient, and the lure should release pheromone at a constant rate. The
trap system also should allow easy maintenance, such as removing
trapped insects, replacing the adhesive catch surface or installing a
new pheromone lure. A permanent trap with a replaceable adhesive liner
can be used for several seasons and may be cheaper in the long run than a
disposable trap used for one season. Permanent traps should be cleaned
periodically to remove contaminants such as spray residues, which could
make the traps repellent to the pest.
Placement:
Place traps in the orchard before the pest starts to emerge. Hang them
within the tree canopy as recommended for the pest being monitored. The
number of traps needed depends on why they are being used. A few
strategically placed traps are all that is needed to establish biofix
for degree-day models. More traps are needed if the objective is to
assess a pest's distribution and density. To assess pest density, traps
should be placed in a grid pattern. Usually the number of moths caught
per trap will increase as the number of traps within an area decreases.
This relationship should be taken into account when comparing data from
different orchards using different trapping densities. It also can be
useful to place traps on the border of the orchard to monitor movement
of insects into the orchard. If the number of insects captured in border
traps is higher than interior traps, it usually signals problems from
an external source. When using the number of insects captured in
pheromone traps as a treatment threshold, always use the trap density
specified.
Maintenance: Traps should be checked at
regular intervals, at least weekly. As the season progresses, the sticky
surface inside the trap can become contaminated with moth scales,
debris, dust or nontarget insects. Any deterioration of the trap's
adhesive surface will reduce its efficiency. Contaminated adhesive
surfaces should be changed as needed. For example, the efficiency of the
wing-type trap declines after an accumulated catch of about 30 moths.
When trapping in blocks where pest densities are low, as is often the
case with codling moth, the adhesive should be stirred after removing
insects to maintain the efficiency of the trap.
Interpreting data: Though the pheromone trap is easy to use, it may not be as easy to interpret the results. Moth capture can be influenced by:
- Density of the male insect population.
- Age of the male insects.
- The effect of wind and slope on male movement.
- Competition from calling females.
- Trap design and size.
- Condition of the pheromone lure.
- Trap maintenance, placement and density.
For
these reasons, moth capture in a pheromone trap provides only a rough
estimate of pest density. However, if pheromone traps are used properly
throughout the season and from one year to the next, they can provide
useful comparative data.
Other types of traps can
be used to monitor insects, including sticky traps (with or without
attractants), light traps and bait traps. Two kinds of sticky traps are
used to monitor flies. They are a yellow panel baited with ammonium
acetate and casein hydrolysate or ammonium carbonate, and a red sphere.
The cherry fruit fly, a relative of the apple maggot, is usually
monitored with a baited yellow panel. Pails containing an ammonia-,
molasses- or terpinyl acetate-based liquid bait can be used to trap
several species of moths. Moths are also attracted to light sources
placed in the orchard. Little is known about the effectiveness of most
bait or light traps so their use in estimating pest density has limited
value.
Degree-day models
Degree-day
models, when coupled with monitoring, enable you to determine the most
effective time for treatment applications. Insect development is
influenced by temperature, and treatments applied on a calendar basis
can often be poorly timed due to fluctuations in weather from season to
season. Many selective controls, such as insect growth regulators and
microbial insecticides, must be applied at a precise time in the pest's
life cycle to be effective.
A degree-day model predicts insect
development by accumulating heat units (degree-days) and associating
these with critical events in its life cycle. Models are usually
initiated at some easily monitored event (biofix), such as first capture
of males in pheromone traps. Thereafter, daily temperatures are used to
calculate degree-days specific to that insect. Degree-day tables for
some key tree fruit pests are available on this web site. The primary
benefit of degree-day models is their ability to predict critical events
in the insect's life history that would be difficult to observe
directly.
Decision making
The
presence of an insect in the orchard is not sufficient justification,
in most cases, to initiate control measures. If an insect is a potential
pest, the severity of the problem depends on the type of damage it
causes and how much damage the grower is willing or able to accept. For
example, indirect (foliage-feeding) pests such as western tentiform
leafminer and white apple leafhopper can be tolerated in higher numbers
than direct pests such as codling moth, which attack fruit. In addition,
it may pay long-term dividends to accept a small amount of fruit injury
from a pest such as pear psylla to allow natural enemy populations to
increase, achieving biological control and thus minimizing the effects
of pest control activities on the environment.
The
economic injury level
is defined as the pest density that causes damage equal in value to the
cost of control. In other words, it is the lowest pest level at which
control becomes economically feasible by weighing the cost of potential
losses due to crop damage against the cost of control. The economic
injury level will be different for different cultivars and will vary
with tree vigor, crop load and the time of year. In addition to
biological components, growers must also factor in the costs and
profitability of their own orchard operations.
Economic injury
levels for direct pests (where a damaged fruit is culled) are usually
easier to establish than those for indirect pests. In reality, economic
injury levels have been determined for very few fruit pests.
The
treatment (or action) threshold
is the density at which control measures must be applied to prevent
pest densities from exceeding the economic injury level. The treatment
threshold is lower than the economic injury level, allowing time for
control measures to take effect. The treatment threshold can vary
depending on the abundance of a pest's natural enemies. Higher densities
can be tolerated when populations of natural enemies are also high. For
example, the treatment threshold for an insect might be 3 per leaf if
there are no natural enemies but 6 per leaf if predators or parasites
are abundant.
IPMf5
Management tactics
A
variety of management tactics can be used to prevent a pest population
from exceeding the economic injury level. Integrated pest management
stresses reliance on control methods that will be the least disruptive
of natural enemies while still providing adequate control of pests.
Synthetic organic insecticides
have been the dominant pest control tactic used in orchards since their
introduction soon after World War II. There are four main groups:
organophosphates, organochlorines, carbamates and pyrethroids. They have
been relatively inexpensive, highly effective and fast acting, often
providing almost complete control. They affect a wide range of organisms
and often kill natural enemies as well as pests. In addition, many
pests have developed resistance to them. These powerful pest control
tools should be used only as a last line of defense against pests.
Natural enemies, selective insecticides and other nondisruptive control
tactics should be given every opportunity to work before broad-spectrum
insecticide are used.
Insect growth regulators are synthetic chemicals that mimic or inhibit natural hormones that govern an insect's development (see
section on Insect Growth Regulators).
When exposed to these chemicals, the insect develops abnormally and
dies. Insect growth regulators have been an important component of IPM
programs in Europe since the 1980s, but none has been registered in the
United States for use on fruit crops.
IPMf4
Botanical insecticides
are derived directly from plant or plant products. The three botanicals
most frequently used to control orchard pests are ryania, pyrethrum and
rotenone. Ryania is extracted from the roots of Ryania speciosa, a
shrub grown in tropical America. Its use in orchards has been primarily
against lepidopteran larvae, particularly codling moth. Pyrethrum is
extracted from flower petals of certain Chrysanthemum species and has a
fairly wide spectrum of activity against insects. Rotenone is obtained
from the roots of certain species of leguminous shrubs grown in
Malaysia, the East Indies, and South America. This insecticide can be
used to control some chewing and sucking insects. Since botanicals are
fairly expensive and generally less effective or have a shorter residual
effect than synthetic organic insecticides, they are used primarily in
production of organic fruit.
Insecticidal soaps
are available to control soft-bodied pests such as pear psylla, aphids,
scales, leafhoppers and mites. Applications must be timed precisely to
coincide with the pest's most susceptible stage and applied frequently
for greatest success. Soaps may have phytotoxic effects on some crops.
The major advantage to using soaps is their low toxicity to natural
enemies, as well as humans.
Diatomaceous earth is
finely milled fossilized shells of fresh water diatoms. The microscopic
silica dust is damaging to soft-bodied insects such as aphids and pear
psylla. It is thought to kill them by physically damaging their
membranes, leading to a loss of body fluids.
Lime-sulfur and wettable sulfur
are used to control fungal diseases and mites, scale insects, aphids
and pear psylla. Both formulations are incompatible with many other
spray materials and if used improperly can be phytotoxic. Sulfur is
toxic to predaceous mites and can be disruptive to integrated mite
control programs if used in summer.
Horticultural spray oils
are produced by distilling and refining crude petroleum oils. They are
often used in combination with other chemicals but can be used alone to
suppress insects and mites. Applied during the dormant or delayed
dormant period, they kill overwintering stages of pests such as scales
and eggs of European red mite. They also inhibit egg laying by pear
psylla females. To date, there are no documented cases of an insect
developing resistance to oils. The mode of action is not clear, but
several mechanisms are suspected including smothering the insect or its
eggs or penetrating the insect's cuticle and interfering with nerve
transmission. Oils can be phytotoxic to fruit and foliage of deciduous
tree fruits. Damage varies with the type of oil (paraffin content,
unsulfonated residue, distillation range, viscosity), the tree species,
application concentration, and the weather before, during or after the
application. Combining oil with certain pesticides or nutrients may
exacerbate phytotoxicity.
Microbial insecticides
are developed from insect pathogens such as viruses, bacteria or fungi.
They have several advantages over traditional pesticides. They are more
selective, usually not toxic to predaceous or parasitic insects, and
have a much less harmful effect on the environment. The bacterial
insecticide
Bacillus thuringiensis (Bt) is effective against
lepidopteran larvae such as leafrollers, peach twig borer and cutworms.
Bt is not a contact insecticide and must be consumed to be effective.
When ingested, the Bt produces a biotoxin which makes holes in the
insect's stomach lining. Bacterial spores then get into the insect's
blood stream and poison it. Once it has consumed a toxic dose, the larva
stops feeding but may remain alive for several days. Bt is most
effective against young larvae, as it takes a smaller dose to kill them
than it takes for more mature larvae. Bt will kill codling moth larvae
in the laboratory, but because they are exposed for such a short time
before entering the fruit (probably not long enough to consume a lethal
dose) it is not a highly effective field control. The codling moth
granulosis virus is a highly selective microbial insecticide. To be
effective, it must be eaten by larvae just after they hatch so sprays
must be applied frequently. Both Bt and viruses have a short effective
life of 3 to 7 days. They break down in sunlight and must be applied
more frequently than traditional insecticides to achieve adequate
control. Because larvae must consume these products, thorough coverage
is essential.
Biological control Biological
control is a pest control tactic where a pest's natural enemies
(predators and parasitoids) are used to keep its density below damaging
levels. Every pest has natural enemies, but whether they can provide
adequate control in an orchard is difficult to predict. To make the most
effective use of biological control you must know the life cycle,
biology and ecology of both the pest and its natural enemies. Biological
control alone will not be sufficient to control all pests attacking a
tree fruit crop, but it plays an important part in an IPM program.
Biological control can either occur naturally or can be encouraged by
introducing natural enemies into the orchard. It also can be enhanced by
protecting natural enemies that are in the orchard and providing
suitable habitat near the orchard or in the cover crop to promote their
survival. Natural enemies have the potential to control many secondary
pests such as mites, aphids, leafminer, pear psylla and grape mealybug.
Broad-spectrum insecticides kill most natural enemies, allowing
outbreaks of pests they would normally control. Biological control is
relatively safe, often permanent and economical. However, it can take
time to implement a biological control program, and it may mean having
to tolerate some crop injury until natural enemies build up to
sufficient numbers to provide adequate control (see also
section on Biological Control).
Mating disruption
In mating disruption, pheromones are used to prevent male insects from
finding females. When used in place of broad-spectrum insecticides for
control of key pests, such as codling moth, it allows improved
biological control of many indirect pests and slows the development of
insecticide resistance. Pheromones are highly specific, affecting only
the target pest, and are not toxic to mammals in the amounts used for
mating disruption. They leave no residues on the crop and have no
adverse impact on the environment (see also
section on Mating Disruption).
Cultural controls
Cultural controls are used to some extent for most apple pests.
However, few provide complete control of any pest on a regular basis.
They are used most often to reduce the potential for pest development
and are combined with other control tactics. Cultural controls include:
- Pruning out water sprouts, sucker growth or foliage preferred by insects such as aphids, pear psylla and leafhoppers.
- Sanitation, including the removal and destruction of infested fruit and pupation sites of key pests, such as codling moth.
- Pruning practices that eliminate optimum sites for mealybug and scales and which enhance penetration of sprays.
- Planting high density orchards with trees that have relatively smooth bark and easily sprayed canopies.
- Managing fertilizer to limit the excessive plant growth preferred by plant-sucking insects.
- Eliminating pests' alternate plant hosts in or around the orchard.
- Maintaining a ground cover that provides habitat for beneficial insects.
