Office of Pesticide Programs
       Integrated Pest Management Unit
          Washington, D.C. 20460
                            May 1980

                  ON CITY SHADE TREES
Center for the Integration of Applied Sciences (CIAS)
                John Muir Institute
               Produced under Contract # 68-01-4475
             for the U.S. Environmental Protection Agency

     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 recognized—for 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.).

     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.


     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

     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.
                             - 2 -


     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:


     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
     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
                              -  3 -

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.

                         •%?••'. --.•;• .'.siT^)
     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.
                                 -  4  -

     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

        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:

     —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,

     --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.
                      - 6 -

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
                               - 7 -

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.

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.
                      - 9 -

     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

     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:


     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

     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.

                             - 10  -

     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

     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

     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.
                              - 11 -

        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

        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.
                                  - 1

     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
                               - I!

             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
                  '..^..•.•-•:.«S-V    ;.....

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.

            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.
                              -  15  -

     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
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.
                           - 16 -

        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.
                          -  17  -

       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

• 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.
                       - 13  -

              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

              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.
                                - 19  -

     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

       For example, nitrogen applications can enhance aphid
       populations; foliar nutrient  sprays may be beneficial to a
       tree in the process of releafing after defoliation.
                        -  20 -

         • 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
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.
                              -  21  -

     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.
                       - 22  -

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

          •  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.
                                - 23 -

             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

             c.  Applicators should read the EPA registered label carefully

                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.
                                - 24 -

     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.
     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

     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 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.
                        -  25 -

     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.
                        - 26 -


     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
        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.
                               - 27  -

                                Appendix A
                    Some Shade Tree Pests and Predators
           in the San Francisco Bay and Sacramento Valley Areas
Common Name
Order and Family
Genus and
ants (in general)    Hymenoptera: Formicidae
aphids (in general)  Homoptera: Aphididae
Argentine ant

ash aphid

bark beetles (in
boxelder bug

caterpillars  (in
Dutch elm disease
elm leaf beetle
European elm scale
fall webworn
fruit tree leaf-
green lacewing
gypsy moth
hawthorn aphid
lady bird beetle
leafhopper, blue-
 green sharpshooter
linden aphid

mites (in general)
oak moth,
pine pitch moth
parasitic insects
predatory insects
Hymenoptera: Formicidae

Homoptera: Aphididae

Coleoptera: Scolytidae

Hemiptera: Miridae


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,
Ceratocystis ulmi
Pyrrhalta luteola
Gossyparia spuria
Hyphantria cunea
Chrysopa carnea
Lymantria dispar
Vespamia sp.
Page #








                                   - 28 -

Common Name


scale insects
 (in general)

shot-hole borer

spider mite

spruce aphid

tulip tree aphid
                                Appendix A
Order and Family
Genus and
Lepidoptera: Notodontidae  Schizura concinna
Homoptera: Coccidae
Coleoptera: Scolytidae
Coleoptera: Tetranychidae  Tetranychus
Homoptera: Aphididae

Homoptera: Aphididae

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                                   - 29 -