INTEGRATED PEST MANAGEMENT
ON CITY SHADE TREES
ENVIRONMENTAL PROTECTION AGENCY
Office of Pesticide Programs
Integrated Pest Management Unit
Washington, D.C. 20460
May 1980
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INTEGRATED PEST MANAGEMENT
ON CITY SHADE TREES
by
Center for the Integration of Applied Sciences (CIAS)
John Muir Institute
Produced under Contract # 68-01-4475
for the U.S. Environmental Protection Agency
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This pamphlet has been prepared by the Center for the Integration of
Applied Sciences (CIAS), a division of the John Muir Institute for Environmental
Studies, Inc., under contract with the U.S. Environmental Protection Agency (EPA),
Region IX.
CIAS has worked for several years under the direction of William and Helga
Olkowski to develop effective integrated shade tree pest management programs for
a number of California cities. Current CIAS work also includes an IPM for flood
control levees for the California Department of Water Resources; development of
urban IPM implementation plans for the California Department of Food and Agricul-
ture; several parasite importation and distribution projects; the development of
an IPM program for the National Capitol Region of the National Park Service
(Washington, D.C.); and an EPA contract to establish a computerized data base
for urban insect pests (including their predators, parasites, habitat, etc.) in
the continental United States. In addition, through a cooperative agreement with
EPA, CIAS is developing a pilot technical assistance center in urban IPM and
alternatives to pesticide use for communities across the nation. A list of the
Center's publications may be obtained by writing to CIAS, 1307 Acton St., Berkeley,
CA 94706, or phoning (415) 524-8404.
The John Muir Institute for Environmental Studies, Inc., is a non-profit
scientific research and educational organization which seeks scientific information
to expand knowledge about natural systems and the role of people in those systems.
It seeks new policy approaches to improve the ways in which society manages, uses,
and protects natural resources. Natural scientists, social scientists, and legal
specialists are brought together to explore a range of technical and policy problems.
Particular emphasis is given to air quality and visibility, energy development,
water resources, forestry practices, chemicals in the environment, and urban
ecosystem management.
The Institute specializes in research problems which have not been widely
or effectively recognizedfor example, visibility as an important national
resource, especially in the West; urban pesticide use; long-range cumulative
impacts of forestry practices; or the interrelationships between groundwater and
surface water in areas subject to intensive energy development. The Institute
is interested as much in the social, economic, and institutional aspects of
environmental problems as it is in the technical and physical aspects. Relevance
to policy issues is a major criterion for the selection of research problems.
Integrated Pest Management on City Shade Trees was prepared with the
assistance of:Diane Kuhn and Lisa Haderlie - drawings
Frederica Bowcutt, Gina Rosenberg and Toby Stewart - layout
and design
Produced under contract 68-01-4475 for the Environmental Protection Agency
Contract Management
Region IX
Robert G. Kuykendall
Jerelean Johnson
Copyright - John Muir Institute - December, 1979
The cover drawing is of Leptocoris rubrolineatus} the boxelder bug, uhich is
usually mistaken for a beetle. It does not harm humans and usually develops
on trees of the maple family (Acer sp.).
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Introduction
As you read this pamphlet, a definition of integrated pest management
will evolve. The definition is complex because it deals with a very com-
/
plex biological system. However, the underlying philosophy that provides
the basis for integrated pest management is very simple.
When your city encounters a pest problem, you first find out as much
as you can about the specific pest causing the problem: its life cycle,
its effect on the tree, its natural enemies, and what can be used to
control the pest that does not disrupt its natural enemies. You then
determine how much damage or how large a population can be tolerated and
then use the methods of control that are the least costly and/or have the
least side effects. The best solution sometimes requires no treatment.
This can be the most satisfying result of IPM - having enough know-
ledge, information, and confidence to pursue the best solution in the
face of public overreaction.
Stan Haugen
Principal Civil Engineer
Department of Public Works
City of San Jose
EPA REVIEW NOTICE
This report has been received by the Office
of Pesticide Programs of the EPA and approved
for publication. Acceptance does not signify
that the contents reflect the views and poli-
cies of the EPA, nor does mention of trade
names or commercial products constitute en-
dorsement or recommendation for use.
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ADVANTAGES OF AN IPM APPROACH
Integrated Pest Management, abbreviated as IPM, is a technical
decision-making system that combines all available pest control tech-
niques into a program for suppressing pest populations below injury
levels.
Why use an integrated pest management (IPM) approach on shade
trees? Because IPM programs have several advantages:
Reduced Pesticide Usage
IPM programs have been shown to reduce pesticide use. This makes
care of the trees less hazardous for the maintenance people. It is
difficult to use .pesticides on trees without getting poisons out in the
general environment and affecting more than the target pest. Thus, a
reduction in such treatments makes the city a healthier place for the
general public. It also permits more birds to survive in the trees (in-
cluding insect-eating birds) and spares many bees which enhance home
garden fruit and vegetable yields.
Less spent for purchasing costly materials means greater budgetary
flexibility for tree maintenance departments.
More Accuracy and Efficiency
IPM makes possible more accurate predictions of when and where pest
problems will occur and the timing of treatments against pests with the
least disruption of their natural enemies. Furthermore, it can tell you
if your treatments were worth the cost and effort. This, in turn, can
increase efficiency in the over-all management of the trees and other
vegetation. These benefits are achieved because an IPM program includes
both a monitoring and an evaluation process.
Public Awareness and Participation
A good IPM program includes public education. Citizens learn that
the presence of many insects in the trees is not by itself reason for
concern. They are given information about alternatives to pesticide use
when problems are serious. As a result they put less pressure on the
municipal street tree maintenance division for unnecessary treatments.
Through learning about the program, citizens are encouraged to adopt less
hazardous methods of pest management in their own backyards. The general
public appreciates the city's effort to provide such educational services
and reduce environmental contamination.
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WHY CHANGE IS NEEDED NOW
Since the end of the Second World War and the growth of the agri-
chemical industry, modern insecticides have formed the backbone of pest
management programs in this country. Unfortunately, a number of problems
with these materials have begun to emerge. Their effects upon human
health and wildlife survival are increasingly well-publicized. Not so
obvious, and thus less understood, is the way in which the unwise use of
insecticides may actually cause more pest problems than they cure. This
is because of:
Resistance
The insect pest populations often become resistant to the chemical
poisons. There are currently worldwide more than 400 species of insect
pests resistant to one or more insecticides. Ants, for example, may be
resistant to chlordane. The more specific a material used against an
insect population, the faster the resistance develops, as only those
individuals that survive each treatment are available to breed the next
generation.
Resurgence
When an insecticide kills off the beneficial insect predators and
parasites, the target pest population can rebound, often reaching a higher
level in less time than it took to build up before the treatment. Not all
natural enemies of all pests are equally susceptible to the effects of all
pesticides. However, many species are more sensitive than the insects they
prey upon to certain materials. Furthermore, natural enemy populations
usually develop more slowly than their hosts, so setbacks at crucial moments
can have devastating effects on their ability to suppress the pest population.
Secondary Outbreaks
Entirely new species of insects and mites may become a problem when
their natural controls are accidentally destroyed by poisons aimed at the
original target pests. For example, mite outbreaks may be caused by
carbaryl treatments aimed at caterpillars or aphids because mite natural
enemies are very sensitive to this compound. (See Figure 1.)
Rising Costs and Restrictions
Since most commercial synthetic insecticides are marie from fossil fuels,
their cost rises as these supplies dwindle and we buy more from overseas.
Furthermore, increasing government restrictions have reduced the number
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of pesticides available, and safety regulations have reduced access to
insecticides and the ease with which they can be used. Thus, there are
reasons besides human and environmental health to find and use alternative
approaches to pest management.
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*
Figure 1. The two-spotted spider mite, Tetranuchus urticae,
speckles leaves with its feeding wounds. Outbreaks
of the "two spot" can be produced by plant stress
or disrupting of natural enemies. The commercially
available predatory mite, Phytoseiulus versimilis,
is very effective acainst this species.
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BASIC CONCEPTS OF IPM
Natural Controls
A sound pest management approach is based on the understanding that
insects and other animal populations are normally under natural control.
Examples of these controls are:
1. temperature and humidity
2. availability of food and habitat
3. disease
4. natural enemies - parasites and predators
Disease and natural enemies are sometimes referred to as biological
controls. Biological control is working all the time. It is the reason
that humans are able to raise any plants on this planet at all. Every
tree contains far more species of potentially serious pests than an un-
trained observer is likely to be aware of. Where no pesticides are used,
these potential pests are under good control by their natural enemies.
Integrated pest management is based on the knowledge that because these
natural biological controls are operating to reduce animal populations,
any treatment should 1) avoid disrupting the natural controls, and 2)
aim to suppress the pest population, not eliminate it. These are dis-
cussed below.
Preserving Natural Biological Controls
All efforts to control pests should strive to disturb the naturally
occurring biological controls as little as possible. Even the pest popu-
lations, damaging insects or mites present in large numbers, have some
biological controls operating upon them. If these are disrupted through
poor management practices, the pest problem may get worse or last longer.
Furthermore, entirely new pest problems may develop sooner or later.
At least four basic strategies can help preserve natural biological
controls.
1. Alternatives to Pesticides
Use alternative methods of pest management rather than a
pesticide whenever possible. Synthetic chemical pesticide*
should be used when all other methods are inadequate and the
situation is judged to be critical and in need of swift action.
Examples of critical situations are:
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where the tree will be seriously damaged or killed.
Slowing down the growth of the tree, as is caused by some
large tree aphid populations, is not necessarily dangerous.
It is desirable to have street trees grow slowly in many
cases. For example, tulip trees can support large aphid
populations without serious damage (See Figure 2). However,
large infestations of the spruce aphid may seriously damage
or kill spruce trees.
--where the pest will defoliate all the leaves of the tree
and the shade is essential during hot weather. Mature broad-
leafed trees can usually lose their leaves frequently without
apparent damage. The energy costs may rise due to increased
air conditioning in nearby houses when the tree is defoliated,
however.
--where the damage is a minor aesthetic one but the citizen
does not accept either the sight of the pest or the slight
change it makes in the appearance of the tree.
2. Selective Pesticides
Always use as selective a material as possible. For example,
if Bacillus thuringiensis is effective, there is no point in
using a wider spectrum material that may cause other pest outbreaks
and/or kill beneficial organisms such as bees or birds.
Water and soap washes can be considered selective, since they
do not damage natural enemy populations as do more toxic materials.
In comparison to the use of hydraulic sprayers or mist blowers,
tree injections offer more selectivity by reduction in drift, and
can be more effective, particularly where trees are large and
the usual techniques are ineffective. More selective materials
are becoming commercially available, and when existing methods
fail, these may prove useful. Even more broad spectrum materials
can be used specifically by isolating the target pest population
in time or space. The boxelder bug (See Figure 3), for example,
can be treated in the nymphal stage at the base of trees early
in the season. But later, when spread out over the trees and
other areas, the adults are virtually impossible to manage. At
this time, insecticide treatment would be wasteful.
3. Spot Treatment
Treat only the area where the problem occurs. Out of every
group of trees of the same type only certain ones are likely to
be seriously affected by the pest problem. Whether the treatment
is water washing or the use of a more toxic pesticide, treat only
where a serious problem exists and leave the minor pest populations
alone. There must be some potential pests around to sustain their
natural enemies. By treating as selectively as possible, year by
year you will let more of the beneficial insects survive to do the
work for you. Slowly the bird and insect life in the tree? may be
brought back into balance again.
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Figure 2. The tulip tree aphid, IIlinoia liriodendri, .first-
invaded California in 1974. Note that aphids have
live births and the adults can be winged or withoui
winqs.
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Figure 3.
This colorful red and black "bug",
Leptocoris rubrolineatus, is usually
mistaken for a beetle. It does not
harm humans and usually develops on
trees of the maple family (Acer sp.J.
However, the female boxelder is their
favorite host.
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4. Timing
Only treat when:
--information from monitoring efforts shows that the pop-
ulations of parasites and predators is not great enough
to suppress the pest population to an acceptable size. This
must be determined separately for each potential pest on each
variety of infested tree.
--the predators and parasites are in the least susceptible
life stage and the pest is most vulnerable. This needs to be
determined for each pest-natural enemy complex. The European
elm scale provides an example here. At times this species
can become a problem and produce excessive honeydew. Treat-
ments should be directed at the young crawler stages that are
more susceptible. This frequently requires delay of treatments
until females have finished depositing young. Scale insects
generally should be treated in the same fashion. Predators
and parasites may be least susceptible as adults rather than
larvae or in the cocoon stage. This needs to be determined
with each organism, site, and material use.
Reduce, Not Eliminate, Pest Problems
Pest management efforts should be aimed at merely reducing
the size of the pest population to the point where no economic,
or only minor aesthetic, damage occurs. The aim is not to
eliminate the pest from the area,' since this will also eliminate
its natural enemies and make the situation even more unstable.
Skillful handling of pest problems will result in finding out
how many potential pests can survive without causing serious
damage and without pest population resurgence. Once this infor-
mation is determined, the population can be maintained at or
below that level.
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IPM COMPONENTS
An integrated pest management program has six basic components,
whether for the shade trees of a city, a cotton field, or the backyard
garden. These components are:
1. Monitoring populations of potential pests and their natural
enemies.
2. Determining aesthetic or economic injury levels.
3. Developing and integrating strategies that affect potential
pest populations.
4. Timing and spot treatment with pest suppression strategies.
5. Evaluating results.
6. Educating maintenance personnel and citizens about natural
enemies of insect pests and strategy combinations for environ-
mentally sound pest control.
These components are described below:
Monitoring
Establishing a monitoring program of populations of potential pests
and their natural enemies involves the following step?:
1. Determine the purpose for the monitoring. For example, you
might establish a monitoring program to time pesticide treatments,
to release lacewings, relate pest population size to weather, or to
discover more about the biology of the pest or its natural enemies.
2. Determine which populations are to be sampled. For example,
in managing most aphids, there are many predators and parasites
that could be monitored. It would be too time-consuming to check
them all. Some may be more important, more easily damaged by treat-
ments, or easier to sample. A decision must be made and monitoring
forms developed and personnel alerted to look for the appropriate
information.
3. Decide on the frequency of visits and which sites should be
inspected. Not all trees of a species can be visited, nor do they
need to be. High priority areas can be visited weekly or more
frequently. Less visible or affected sites can be checked just
often enough to compare with the others.
4. Determine the number of trees to be sampled at each site. It
usually takes two or three seasons to determine the minimal, number
that can be checked and still provide reliable information on which
to base decisions.
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5. Decide upon a precise sampling procedure. For example, you
may need to count how many aphids there are on 25 leaves on the
north, south, east, and west of the middle canopy of the tree; or
how many caterpillars an inch long are found on the last 12 inches
of ten shoots picked at random while walking around the tree. It
will also probably take two or three seasons to determine the least
amount of sampling and the best way to obtain reliable data. More
than one technique or sample size may have to be tried to determine
this.
6. Make an easy-to-use recording system. Once in the field, it
is essential that the minimum time be used in sampling. The person
doing the sampling should have a minimal amount of writing to do:
location, date, and their initials. Everything else should be
recorded by checking off or circling the appropriate number or
comment. It may take several revisions to arrive at the most use-
ful record sheet.
7. Develop a system for display of field data for ease in decision-
making. As the season progresses, and at its end, the information
collected in the field through the monitoring process must be
assembled in a meaningful way so that patterns emerge upon which
decisions can be made. In street tree maintenance the most common
correlations are made with the weather (temperature and rainfall
primarily), geographic location and pest population size. By
including geographical location data, you can consider soil types,
drainage, and management factors in adjacent areas.
8. Evaluate the sampling and decision-making system. This is
one of the most important parts of the monitoring system. As you
move through the seasons and begin to collect and assemble data,
including weather variations from season to season, you may discover
reasons to make changes in the process. If the sampling system did
not adequately warn of key population trends, then it should be
redesigned.
9. Make corrections in the sampling and decision-making system.
Your evaluations may suggest that greater accuracy and/or efficiency
can be achieved through changing parts of the process. Everyone
working on developing the new process must remain flexible so that
procedures can be modified.
Determine Injury Levels
There are three components to determining injury levels. The first
is deciding how much aesthetic or economic damage can be tolerated. The
second is determining how large a population of insects must be to cause
that much aesthetic or economic damage. The third is fixing an "action'7
or "treatment" level.
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In the San Francisco Bay and Sacramento Valley areas there are few
insect pests that, if left under good natural control, will cause loss of
established trees (economic damage).* Caterpillars and beetles can'cause
the most visible damage, but defoliated elms and oaks will defoliate rather
quickly.
Contrary to popular belief, in most cases an occasional total loss of
leaves due to insect feeding or other types of severe pruning will not kill
mature trees. However, repeated total defoliation might seriously deplete
stored reserves. Large numbers of coast live oak, Quercus agrifolia, and
holly oak, £ ilex, for example, can be observed to refoliate repeatedly
during outbreaks of the California oakworm (See Figure 4) without death or
damage, unless they have already been weakened from other causes, such as
overwatering in the dry season.
Figure 4. The adult ((right) of the California
oak moth, or oakworm, Phruaanidia
califormica, sometimes occurs in
large numbers which may be unnecessarily
alarming. The above pictures the
most important parasite, Itovlectis
beherensis, stinging the pupal (cocoon)
state of this insect.
* There are a number of diseases that will kill trees in the central
California valley and coastal area: verticillium wilt and oak root
fungus are examples. Positive identification of tree diseases is often
difficult without a laboratory, and little or nothing can be done for
the most serious of the disease problems. Because of its complexity,
the subject of plant diseases is beyond the scope of this pamphlet.
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Both defoliation and the removal of plant juices by leaf-feeding
aphids can slow the growth of trees which, in many situations, may be
desirable. Growth retardants have been used in the past to achieve
similar effects. The spruce aphid may be an exception; there are records
of its killing mature trees in the northwest.
Bark beetles usually attack injured or dying trees. The European
elm bark beetle, which vectors the Dutch elm disease pathogen, fits this
category. The best approach to these insects is selection of tree species
suitable to the locality and good over-all care of the trees including
careful pruning and removal of dead wood.
Most other tree insect problems normally encountered involve changes
in the appearance of the tree, insect products or habits annoying people,
insects leaving the tree and causing damage to adjacent vegetation, or
simply insect visibility. Each of these is discussed below.
Changes in the appearance of the tree. (Aesthetic injury).
An example of this category is the defoliation of the native
and imported "live" (evergreen) oak trees by the California oak-
worm or oak moth. This is a periodic occurence in which severe
defoliation may be experienced two or three seasons in a row but
may not be seen again in the same area for three to seven years.
(See Figure 5.) Where selective materials like Bacillus thurin-
giensis are used, many natural enemies of the pests are spared
and oak moth outbreaks may be shortened, more confined in area
and less severe when they do occur.
Figure 5. The predatory bug Podisus vallens feeds on larvae
of the oak moth. Note the characteristic damage
to the leaf caused by later stages of the oak moth
larvae.
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The aesthetic injury level will vary depending on the
location of the tree. For example, in a school district, trees
lining the main entrance to the school buildings are highly
visible. These should claim priority in protection against
noticeable defoliation. Trees in the parking lot or around
maintenance buildings may be allowed a somewhat greater degree
of leaf loss. Those at the rear of the playground, where they
form a creekside "natural" area, can be treated as lower priority
and in many cases, left to refoliate naturally. They probably
will benefit during the winter rains from the caterpillar
manure because the caterpillar droppings release the plant
nutrients in the normally decomposition-resistant leaves and
make them available to the tree again.
The red-humped caterpillar (Figure 6) and the elm leaf
beetle (Figure 7) are two other common defoliators present in
the .San Francisco bioregion. In determining injury levels, the
same sensitivity to site should be used as with the oak moth.
The aesthetic injury level is not the same for each place in
the city where a susceptible tree exists, and the monitoring
program and levels set for treatment should reflect this.
, r
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Figure 6. Schizura Qoncinna, the red-humped aaterp-illar^ is
native to California and moves from walnut orchards
to sweetcums. It is susceptible to Bacillus
thurinaiensis and is attacked by a number of parasites.
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Identifying the aesthetic injury level and adopting a
monitoring and treatment program can be complicated, but the
end result justifies the effort. Also, frequently the applic-
ation of the "aesthetic level" concept remains a subjective
matter, since opinions can differ between maintenance personnel
and the public as to what is intolerable.
Figure 7. Tne elm leaf beetle, Purrhalta luteola, feeds on
the leaves of most elms. Probably originating
from the Middle East, it is a major pest problem
in Europe and the United States.
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Insect habits or products causing annoyance.
Where aphids (Figure 8) or leafhoppers (Figure 9) occur
in abundance, the dripping of honeydew upon sidewalks and cars
or the falling of shed aphid skins may be annoying. Honeydew,
(which is used as human food in some countries) is the sugar-
protein excretions of certain insects that suck plant juices.
Heavy honeydew accumulations on leaves of some trees can lead
to the growth of a black "sooty" mold which is undesirable to
some people. In some cases, occasional washing down of the
trees with plain water (or soap and water) may be all that is
needed.
V
Figure 8. The Linden aphid, Eucalliyterus tiliae, originally
from Europe, no longer produces troublesome honey-
dew where its parasite Trio_xus curvicai'.f'ii? is
introduced to control it.
The leafhopper called the blue-green sharpshooter,
Grgyhocevhala atrovunctata, is a vector of Fierce 's
disease in grapes. It occurs on a number of shads
trees, particularly the young growth of sweetgims,
and can produce a copious yet light misty honeydew.
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For this method to be most effective, it should be timed so
that the aphids' natural enemies are in the least susceptible
stage. For example, when ladybeetles are in the pupal stage, they
are attached to the leaf and are relatively resistant to washing.
The strength of the spray should be adjusted to wash off honeydew
and live aphids while leaving most parasitized aphids, or
"mummies", as these are called, in place. (See Figure 10.)
When the parasitized aphids are left on the tree and many of the
pests washed off, the proportion of pest to natural enemies
has been changed radically. The emerging parasites can then
have a great impact on the pest population.
,-iqure 10. Tlie parasitized aphids or "mummies" can commonly
be seen in colonies of live aphids if you look
carefully. They are usually shinier and rounder
than the live aphid, a different color (tan, whits,
or black) and stiff avvearinc.
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Tolerance for honeydew drip will vary greatly according
to whether cars and/or people will be directly affected.
Injury levels must be set accordingly. Higher populations of
aphids and honeydew production can be tolerated on trees in
lawns, bare earth or mulched areas than on those branching
over sidewalks and asphalt where heavy human or auto traffic
occur.
Insects leaving the tree and causing damage to adjacent vegetation.
Caterpillars, such as the fruit tree leaf-roller, may leave
the trees and crawl or drop down to adjacent vegetation. In some
cases this is an example of people being annoyed at the sight of
the insect. In other situations more or less severe damage to
adjacent vegetation may occur. The education of the citizen
through use of hand-out sheets, telephone calls, and face-to-face
discussion is important. When that fails, or the situation is
intolerable, the properly timed use of a selective material like
Bacillus thuringiensis is the best approach. However, treating
the tree at such times may be ineffective since the great majority
of the caterpillars may have already left the tree to wander, eat
elsewhere, or pupate. Where they are feeding excessively on
on plants or beneath such trees, Bacillus thuringiensis can be
used to treat that vegetation. For each location and problem,
it needs to be determined when the most susceptible stages occur.
Visibility of the insects.
Occasionally, it will be the sight of an insect population
that may disturb the citizens and thus cause a problem. Good
examples are the boxelder bug, found on boxelder trees and a
few other maples, and fall webworms, which form large silken
tents in sweetgums and native walnuts (Figure 11).
,:Vm&:«T <'-**.&$$*&%
Figure II.
Hvvhantria cunea, or fall
webuorm, shown inside its
tent. These webs are usually
more unsightly than they are
damaging and are often easily
removed by pruning.
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Boxelder bugs do little noticeable damage to their host
tree and none at all to the foundation shrubbery or areas inside
the house where they may collect in large numbers when looking
for overwintering sites. The citizen must be taught that these
bugs are harmless and learn how to screen and exclude them with
putty or caulk from the house. Indoors or out, they can be swept
up or vacuumed.
Fall webworms may elicit strong fear reactions from some
people. Where possible, using a pole pruner to cut out the tents
and placing the prunings in plastic bags to cook in the sun has
the advantage of being simple and providing education for the
citizen. It is desirable to convey the point that physical controls
should always be chosen before resorting to chemical methods of
insect management. Where the tents are too high or numerous to
manage with a pole pruner, a selective material like B.t. can be
used very satisfactorily, sprayed directly into the cenTer of the
webs.
Where the visibility of the insect is a problem, it is
necessary to determine first who thinks so. Education should be
aimed at helping people to tolerate some level of insect presence.
Tolerance will vary from spot to spot. In many cases no treatment
other than education is needed.
Strategies to Control Pest Populations
There is already available a wide range of strategies for pest control.
In relation to each street tree insect problem, they should be considered
in the following order:
1. Plant, selection
For replacement and new plantings, tree species and varieties
should be selected that offer some resistance to the known pest
problems of the area. This requires input into those managerial
levels where these decisions are made. Frequently, landscape
architects are unfamiliar with the pest management consequences
of their recommendations. Wholesale nurseries may need one or
two years' lead time if pest problems call for planting varieties
that are not currently available in sufficient quantity.
Street tree personnel can aid in the development of low main-
tenance varieties by identifying and observing consistently resis-
tant specimens. These should be called to the attention of
nurseries, arboretums and horticultural societies. In some cases,
vegetative propagation from these specimens will provide new and
better plant materials for the local urban areas.
2. Diversity of planting.
Increasing the diversity of tree species can reduce maintenance
costs and the aesthetic impact of pest prc'-lems.
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Insect problems on various tree species appear at different
points during the season. At any one time, only a small number
of trees must be monitored closely, e.g., for aphids in the spring,
for fall webworms at the end of the summer. Mixed plantings make
it less likely that huge populations of host-specific insects
will have an opportunity to develop. When they do, the visual impact
upon a specific street is reduced if the particular species affected
is surrounded by other trees of different species not attacked by
the same insect. Mixed plantings also offer the same protection
against disastrous aesthetic impacts from disease outbreaks.
3. Habitat Modification
Changing the environment in some manner often will discourage
the potential pest or encourage its natural enemies. Mulching
with wood chips or compost beneath the tree, modifying drainage,
wind or light conditions, removing or adding nearby plants may
be helpful. Mulches, for example, modify the habitat by increasing
moisture at the soil surface, decreasing temperature ranges and
changing or buffering soil pH. Clustering Monterey pines may
discourage attacks on pine pitch moth which may prefer to attack
single exposed specimens under stress from heat or sun. Many of
these approaches might be described equally well under the
following categories of cultural and physical controls.
4. Cultural controls.
Most horticultural practices have the potential for encouraging
potential pests or for suppressing them by encouraging their
natural enemies. Often maintaining tree health is the key, since
vigorous plants are more likely to repair or outgrow insect damage
or to be less attractive to potential pests such as borers and
bark beetles. The following are examples of cultural controls.
Modify the watering program to improve tree vigor.
Decrease water. For example, native live oaks should be
located in areas of good drainage, away from sprinkler
systems, with ground covers that do not require watering.
Grading around all trees should encourage movement of water
away from the area where the trunk joins the roots. Standing
water encourages a wide variety of plant pathogens that
attack roots of the tree.
Increase water. For example, trees such as sweet gums may
be more susceptible to red-humped caterpillars when under
stress from lack of water.
Modify fertilizer availability to the tree or adjacent
vegetation.
For example, nitrogen applications can enhance aphid
populations; foliar nutrient sprays may be beneficial to a
tree in the process of releafing after defoliation.
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Protect young or especially sensitive trees from sunscald,
wind, rodent damage, or potential human damage from accidents
and vandalism.
5. Physical controls.
Pruning is the most common physical control used successfully
to reduce pest problems. Pruning can be used to reduce aphid popu-
lations on ashes, if the population is small. On hawthorns, removing
the sucker growth, which is the favored habitat of the hawthorn
aphid, can reduce populations. The tents of fall webworms can be
pruned out, as mentioned previously. One of the most important uses
of pruning is to remove diseased, injured or dead wood so as to reduce
the attraction of the tree to bark beetles, such as those that spread
the Dutch elm disease, or borers such as the shot-hole borers that may
invade city trees from nearby orchards.
Water washing may also be considered a physical control where
it is used primarily to knock off of the trees insects that cannot
fly back again, e.g., immature aphids and leafhoppers.
6. Barriers.
At least one ant species in the area, the Argentine ant,
commonly climbs into the trees to obtain honeydew, nectar and
possibly other food (Figure 12}. This ant is known to frighten
away or kill certain natural enemies of many potential pest insects,
such as aphids and scales. Where ant columns are seen climbing
the trunk, (best observed during the cooler hours or on the shaded
side of the tree), ringing the tree with StickemR, a commercially
available non-toxic adhesive, may help substantially in pest
management.
Figure 12. Ants frequently harvest honey dew from aphids (as well as
from other honeydew producers) and actively protect them
against their natural enemies. Thus protected, the aphid
populations can increase, which in turn produces over-
abundant honeydew. Honeydew can be used as a food, and
is believed to be the "manna" of the Bible. It is still
collected from certain scale insects in the Middle East
and sold as a candu in the bazaars.
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The sticky strips should be three or four inches wide,
completely circle the trunk, out of reach of pedestrians, just
below where the limbs branch out from the trunk, and thin enough
to prevent dripping. This sticky ring will need to be renewed
yearly. This ringing should be done early in the season before
large populations of the honeydew producers are attracting ants
into the tree, since those ants cut off fron the ground by the
sticky barrier will remain alive in the tree to cause problems
for a long period.
Lights and smells can both be used to attract various poten-
tial pest insects to traps for the purpose of either counting or
killing them. Most promising attractants are the various pheromones,
external hormones or chemical signals produced by insects to attract
the opposite sex. Pheromones are already commercially available
for trapping elm bark beetles and gypsy moths, and more are likely
to become available in the future.
Locally the use of traps has been primarily to sample insect
populations during the monitoring process for the purposes of
deciding whether treatment is necessary. Such trap catches can
help determine when and where insect populations occur and to
evaluate the effectiveness of treatments. In other countries,
(China is one example), traps are used extensively to reduce
insect populations. Possibly ingenious methods will be worked
out for their use in managing some of our local problems as well.
8. Biological controls.
Strategies for using biological controls can be described as
falling into the following categories:
Conservation.
This is the strategy stressed so far in this pamphlet.
It refers to conserving the natural controls already present.
Augmentation.
This refers to methods used to enhance or increase bio-
logical controls already present. Using Wheast as a food
spray for lacewings (Figure 13) and ladybird beetles or
nest boxes to encourage insectivorous birds would be examples
of augmenting biological control. Wheast^ is a commercially
available powder, a by-product of cheese-making, that operates
as an attractant to certain predators and parasites. It is
a food substitute for naturally occurring honeydew produced
by many pest insects.
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Figure 13.
This is the adult of the California green
lacewing} Chrusova cornea, a common predator
in warmer areas and commercially available
in the egg stage.
Innoculation.
Releasing Bacillus thuringiensis spores or lacewing eggs
is an example of using innoculation techniques. Here, living
material is being used like a biological insecticide, the
result being a short-term suppressive effect upon the pest
population.
Classic biological control - importation of natural enemies.
In those cases where the pest insect has invaded from
another area and left its natural enemies behind, efforts
may be made to seek out and import those that are specific
to the pest. While the importation effort may be undertaken
under the auspices of the U.S. and state departments of
agriculture and/or a research institution, the successful
establishment of the imported insects in the city trees
depends on the intelligent maintenance of the trees by city
personnel. Often three to four years may elapse between the
introduction of the natural enemy of the insect and a
noticeable effect upon the pest population. A plan must
be developed for tree management during this interim period
that permits enough of the pest insect to survive so that
its introduced natural enemies have a chance to build up
their numbers.
9. Chemical controls.
Pesticides are registered for specific site use, rates of
application, pest timing and application methods. Directions for
use and precautionary statements will be found on the EPA regis-
tered label.
a. Materials should be selected that are
1) the most selective available for the job,
2) the least hazardous to the applicators,
3) the least hazardous to the health of the general
public in regard to short- and long-term effects, and
4) the least likely to be persistent in the environment
and to magnify in food chains.
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b. The application method chosen should
1) minimise drift or other contact with non-target
organisms, including humans,
2) provide sufficient coverage so as to deliver the
proper dose to the target insect,
3) be practical for use at a time when maximally effective
and for causing least mortality to pest natural enemy
populations.
c. Applicators should read the EPA registered label carefully
and:
1) utilize all safety equipment,
2) utilize the proper dosage,
5] prepare only as much material as is needed, and
4) store or dispose of excesses safely.
In general, no single approach to a pest problem is likely to be
successful everywhere and at all times. Often a number of strategies need
to be orchestrated to achieve suppression of the pest below injury levels.
For example, in managing European elm scale, a dormant oil spray against
the adults in the winter may be coupled with soap and water washing when
the crawlers are active in the summer. In managing Dutch elm disease,
sanitation, thorough careful pruning out of dead and dying wood, and
immediate removal of dead or dying trees is the first line of defense.
This should also be coupled with severance of root grafts between infected
and neighboring trees by chemical or physical means where possible.
In general, chemical controls should be reserved for use as a last
resort when a combination of other methods (including education of
citizens] does not suppress the pest population below injury level.
Timing and Spot Treatment
Regardless of what pest suppression strategies are used, it
is necessary to determine:
when a specific strategy can be used so as to minimize harm
to natural enemy populations;
what is the response time, that is, the time between the
decision to treat and when treatment actually occurs (e.g.,
two to three days); and
when is the best time to treat with respect to pest populations.
Using the above information plus weather observations and
previously determined injury levels, calculations can be made on
the time for action and, where B.t. or water or soap sprays will
be employed, the ideal dosage and pounds of pressure for application.
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In the case of elm scale or the hackberry scale, the best
time to treat is when the immature scales or crawlers are present
or when the tree is dormant and overwintering adults occur. Mid-
summer scale treatments are usually ineffective. Out of every
group of trees of the same species, usually only a certain small
number will require treatment of any kind. The monitoring process
will reveal where the problem is likely to become severe enough to
require some action, and treatment should be confined to those spots.
Evaluation
After any kind of technique is used to affect populations, the
site must be revisited to determine the effect of the treatment
immediately, during the rest of the season, and during following
seasons.
Immediate checks should be made of
1) the effect on the pest population and whether it was reduced
below injury levels;
2) the effect upon the pest's natural enemies;
5) possibly phytotoxic (plant-harming) effects upon the tree;
4) the further growth of the pest population; and
5) key records of treatments, field data and evaluations.
Education
Education is a key component of an urban IPM program.
Successful achievement of objectives frequently depends upon the
citizens' understanding the need to develop new ways of dealing
with insect pests in the city and acceptance of the methods that
the city intends to employ. In many cases, human and environ-
mental health concerns necessitate tolerance of more signs of
insect presence in the trees than was generally accepted during
the 1950's and 60's before the full ramification of exclusive
reliance on insecticide use for pest control was understood.
Because of a general fear of insects and a lifelong conditioning
to demand an unnatural level of unblemished vegetation, in many
cases attitudes may be very slow to change and may hamper efforts
to establish functioning IPM programs.
Education efforts should be developed to meet the needs of
maintenance crews and gardeners, using in-service training through
programs that combine meetings (in which the program is explained
and discussed), slide shows and live exhibits (to acquaint the
personnel with the stages of the pests and their natural enemies) ,
and reading materials on integrated pest management. Also useful
are field trips with an IPM specialist to learn about the
monitoring process.
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Similarly, educational efforts should include office
personnel, park naturalists and others who come into contact
with the public. One especially effective tool is the hand-out
sheet, which can be mailed to citizens who inquire about tree-
pest problems, handed to citizens who ask questions of personnel
monitoring the trees, and distributed through public libraries,
schools, and other public institutions and participatory groups.
In some instances, newspaper and radio messages may be feasible
and effective.
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DEVELOPING NEW IPM PROGRAMS
Few cities or institutions will have on their staffs personnel
adequately trained to develop an IPM program for the shade trees. In
some cases such a program has already been worked out for a nearby city
with the same mix of tree species and insects under the same weather
conditions. Then it may merely be adopted in the new locality. In some
cases extension personnel and university researchers may be able to advise
about specific problems. Frequently, an IPM specialist may be needed to
develop and maintain a total program. However, where desirable, the tech-
nology can be transferred to the street tree maintenance personnel, if the
personnel and commitment are present.
The length of time it will take to develop an IPM program for the
shade trees of any city of institution depends on a number of factors:
A. The total number of trees.
B. The number of tree species.
C. The readiness of the maintenance and supervisory personnel to
make changes.
D. The public acceptance of the program.
E. The human and financial resources that can be applied to the
program.
F. The number of insect and disease problems.
G. The severity of these problems
H. The previous pattern of insecticide use.
I. How much is already known about the life cycles and natural
enemies of the insects causing pest problems.
J. The number of major invaded insect pests against which it is
feasible to import natural enemies.
In any case, to develop an IPM program it generally takes more than
one season -- sometimes three or four -- to determine reliable injury
levels and the best alternatives to pesticides for local use in pest
suppression. However, the resulting program, if consistently followed
by those responsible for vegetation maintenance, develops controls which
have long-term effectiveness.
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Appendix A
Some Shade Tree Pests and Predators
in the San Francisco Bay and Sacramento Valley Areas
Common Name
Order and Family
Genus and
Species
ants (in general) Hymenoptera: Formicidae
aphids (in general) Homoptera: Aphididae
Argentine ant
ash aphid
bark beetles (in
general)
boxelder bug
caterpillars (in
general)
Dutch elm disease
elm leaf beetle
European elm scale
fall webworn
fruit tree leaf-
roller
green lacewing
gypsy moth
hawthorn aphid
lady bird beetle
leafhopper, blue-
green sharpshooter
linden aphid
mites (in general)
oak moth,
California
pine pitch moth
parasitic insects
predatory insects
Hymenoptera: Formicidae
Homoptera: Aphididae
Coleoptera: Scolytidae
Hemiptera: Miridae
Lepidoptera
Coleoptera: Chrysomelidae
Homoptera: Eriococcidae
Lepidoptera: Arctiidae
Lepidoptera: Tortricidae
Neuroptera: Chrysopidae
Lepidoptera: Lymantridae
Homoptera: Aphididae
Coleoptera: Coccinellidae
Homoptera: Cicadellidae
Homoptera: Aphididae
class Acarina
Lep idopt era: D iopt idae
Lepidoptera: Aegeriidae
Hymenoptera, Diptera
Hemiptera, Anthocoridae,
others
Iridomyrmex
humilis
Prociphilus
fraxinifolii
Leptocoris
rubrolineatus
Ceratocystis ulmi
Pyrrhalta luteola
Gossyparia spuria
Hyphantria cunea
Archips
argyrospilus
Chrysopa carnea
Lymantria dispar
Graphocephala
atropuctata
Eucallipterus
tiliae
Phryganidia
California
Vespamia sp.
Page #
3,21,22
3,6,10,11,13,16
17,18,20,21
21
21
12,13,20,21,22
6,8,18,19
3,11,12,14,18,20
13,21,24
13,14,15,22
9,24,25
18,19,20,21
18
22,23
2-2
21
17,22
16,21
16
3,5
12,15,14
20
9,10,22
9,10,22
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Common Name
red-humped
caterpillar
scale insects
(in general)
shot-hole borer
spider mite
spruce aphid
tulip tree aphid
Appendix A
Cont'd.
Order and Family
Genus and
Species
Lepidoptera: Notodontidae Schizura concinna
Homoptera: Coccidae
Coleoptera: Scolytidae
Scolytus
rugulosus
Coleoptera: Tetranychidae Tetranychus
urticae
Homoptera: Aphididae
Homoptera: Aphididae
Elatobium
abietinum
Illinoia
liriodendri
Page #
14,20
9,21,25
21
4
6,13
6,7
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