LESSON 1: PEST CONTROL OVER THE YEARS developed resistance to every major group of

insecticides, making control with chemicals difficult, if

Mystery surrounded the causes of crop failures and not impossible, to achieve. Growing concerns about the
human and animal diseases for many centuries. The first environmental and health hazards associated with
pest control measures were crude—weeds were pulled, pesticides have also become significant factors
rats were clubbed, and beetles were plucked from challenging pesticide use. In 1962, Rachel Carson
foliage. The earliest use of chemicals as pesticides dates published Silent Spring, a book that examined pesticides
back to 2500 B.C., when sulfur was burned to control and their effects on the environment. DDT and other
insects and mites. Through the years, experimentation chlorinated hydrocarbons were her primary concern
and good fortune led to the recognition of additional because of their stability and persistence in the
chemicals with pesticidal activity. Early plant-derived environment. Their long residual activity was a major
insecticides included hellebore to control body lice, factor contributing to their effectiveness, but a negative
nicotine to control aphids, and pyrethrins to control a effect was their ability to accumulate in the fatty tissue
wide variety of insects. Lead arsenate was first used in of some animals (bioaccumulation). In certain
1892 as an orchard spray. In France during the late 19th situations, biomagnification of the insecticides
century, a mixture of lime and copper sulfate was occurred. Biomagnification is the process whereby
sprayed on grapevines to deter passers-by from picking some organisms accumulate chemical residues in higher
the grapes. The farmer found the mixture also concentrations than those found in the organisms they
controlled downy mildew, a serious fungal disease of consume. Ecologists refer to a food chain as the
grapes. Later named Bordeaux mixture, it remains a sequence of animals feeding in the natural
widely used fungicide worldwide. Until the 1940s, pest environment. A particular plant, animal, or
control chemicals were derived from plants and microorganism is eaten by an animal, which is in turn
inorganic compounds. During World War II, DDT, a eaten by another animal. At each succeeding level, an
synthetic chemical, played a very important role, saving animal normally eats a number of individuals from the
Allied soldiers from insect-transmitted diseases. DDT previous level. Figure 1.1 depicts how biomagnification
was hailed as the insecticide to solve all insect of a pesticide can occur in a food chain. Organisms with
problems. The introduction of countless other synthetic pesticides in their tissues are eaten by fish, which are in
organic pesticides followed. These synthetic products turn eaten by birds. The birds at the top of the food
launched the modern-day chemical industry and began chain accumulate the highest concentration of pesticide
a new era in pest control. Given significant success at a residues. Since the publication of Silent Spring, the
relatively low cost, pesticides became the primary United States has experienced a level of environmental
means of pest control. They provided season-long crop awareness and interest second to no other period in
protection against pests and complemented the history. The U.S. Environmental Protection Agency (EPA)
benefits of fertilizers and other production practices. was created in 1970 with a mandate from Congress. Its
The success of modern pesticides, particularly in task was then, and remains today, to implement by
agriculture and human health, encouraged widespread regulation the laws passed by Congress to protect the
acceptance and eventual reliance on them. In recent environment and the health of humans and other
years, however, some drawbacks of heavy dependence animals. Since the 1972 EPA ban on DDT use in the
on pesticides have become increasingly apparent. One United States, regulatory action has been taken against
of the most disturbing is the development of pest many chemicals, including pesticides, thought to pose
resistance to pesticides. Since the resistance of the San significant environmental and health hazards. Public
Jose scale to lime sulfur was recognized in 1908, concern has led to stringent regulation of pesticides and
hundreds of insects have become resistant to one or changes in the types of pesticides used.
more pesticides worldwide. Pesticide resistance also has
arisen in more than 50 weeds and many plant
pathogens. A dramatic example is the Colorado potato
beetle in the eastern United States. This insect pest has
PEST RECOGNITION damage. Often the pest’s host (the animal or plant on
which an organism lives) and location are important to
Pests are organisms that cause problems in various making positive identifications. Information on the
ways. Some compete with people for food or fiber. environmental conditions where you collect pests and
Others interfere with the raising of crops, livestock, or the time of year of collection provides clues to the
poultry. Certain types of pests damage property and pest’s identity. Pest species may have different physical
personal belongings or disfigure ornamental plantings. forms depending on their stage in their life cycles or the
Others transmit or cause plant, animal, or human time of year. Weed seedlings, for example, often do not
diseases. Before trying to control a pest, you need to resemble the mature plant. Many insect species
identify it. Be certain any injury or observed damage is undergo changes in appearance as they develop from
actually due to the identified pest and not some other eggs through immature stages (nymph, larva, pupa) to
cause. Once you have identified the pest and confirmed the adult form. Characteristic Damage Pests may leave
that it is causing damage, become familiar with its life signs of their presence or damage that help you
cycle, growth, and reproductive habits. Then, use this determine what they are. Birds and rodents build nests
information to form your pest control plans. that are often characteristic to each species. The type of
Misidentification and lack of information about a pest feeding damage helps you identify many insects.
could cause you to choose the wrong control method or Rodents and some other mammals dig distinctive
apply the control at the wrong time. These are the most burrows in the ground and often leave identifying gnaw
frequent causes of pest control failure. In addition, marks on tree trunks or other objects. Sometimes trails
some plants are damaged by non-living agents. These in grass or tracks in dirt are helpful clues to rodent
include such things as weather extremes, air pollutants, identification. Insect and rodent fecal materials also are
road salt, and inadequate or excessive fertilization. distinctive and important identification aids. Weeds may
Sometimes this damage is mistaken for that caused by have unique flowers, seeds, or fruits, or unusual growth
living pests. Ways to Identify Pests Identify a pest by habits. Fungi and other pathogens often cause specific
using the guidelines included in this chapter and then types of damage, deformation, or color changes in host
consulting reference materials such as identification tissues.
books, Extension bulletins, and field guides that contain
pictures and biological information on the pest. Another PEST MANAGEMENT METHODS
option is to have pests examined and identified by pest
management specialists. When having pests identified, Once a pest problem is anticipated or identified, you
can begin planning your pest management program.
always collect several specimens. Have plastic bags,
vials, or other suitable containers available when You must know what management methods are
available and the benefits and limitations of each. Select
collecting samples in the field. For plant diseases,
submit undamaged specimens, such as healthy foliage, methods that are the most effective and the least
harmful to people and the environment. Whenever
along with the damaged foliage. For insects and their
relatives, kill them first and send them to the specialist possible, combine the use of several compatible
methods into an integrated pest management (IPM)
in a manner that will not damage body parts that aid in
their identification. For weed/plant samples, it is best to program, and target the pest at the most susceptible
stage for control.
submit whole plants, including roots, vegetative
structures, and flowers, if possible. Plants may be Pest Management Methods Natural controls Applied
pressed flat between paper or cardboard to prevent leaf controls  
crinkling or placed in plastic bags. Be sure to include the •  Biological control  
location and date of the collection. The difficulty in •  Mechanical control  
identifying certain insects and most mites, nematodes, •  Cultural control  
•  Physical/environmental   modification  
and plant pathogens in the field is their small size.
•  Host resistance or genetic  control  
Accurate identification requires the use of a hand lens
•  Chemical control  
or microscope, special tests, or careful analysis of
Regulatory Methods studied as biological control agents for certain weeds
Natural controls are the measures that check or destroy and some insects. General predators such as praying
pests without depending on humans for their mantids and lady beetles are sold with claims made for
continuance or success. Natural controls include biological control. In many cases, however, their
climatic factors such as wind, temperature, sunshine, effectiveness has not been established. Maintaining
and rain. Topographic features such as rivers, lakes, and populations of natural enemies by avoiding damaging
mountains can influence pest movement. Naturally cultural practices or the indiscriminate use of pesticides
occurring predators, parasites, and pathogens can can be one of the most economical means of control. If
regulate pest populations. When natural controls have pesticides are part of your control program, select types
not held pests in check, humans must intervene and that are known to be less toxic to natural enemies or, if
apply pest management controls. applied controls recommended, apply pesticides at lowerthan-label rates
include biological, mechanical, cultural, physical, to avoid harming natural enemies. Sometimes it is
genetic, chemical, and regulatory methods. possible to modify certain parts of the environment,
such as by planting crops or ground covers, to maintain
Biological Control . Most pests have natural enemies
or enhance natural enemies.
that control or suppress them effectively in some
situations. Natural enemies, including pathogens, are Mechanical Control. It involves the use of devices,
being used successfully as biological control agents to machines, and other physical methods to control pests
manage certain insect, mite, fungal, fish, and weed or alter their environment. Traps, screens, barriers,
pests. Biological control is often directed against pests fences, and nets are examples of devices used to
that are not native to a geographical area. Introduced prevent pest activity or remove pests from an area.
pests are often problems in their new location because
they lack natural enemies to help control them. Cultivation is one of the most important methods of
Biological control involves locating the native home of controlling weeds. It is also used for some insects and
an introduced pest and finding suitable natural enemies other soil-inhabiting pests. Mechanical devices such as
there. After extensive testing and evaluation, selected plows, disks, mowers, cultivators, and bed conditioners
natural enemies are imported, reared, and released. If physically destroy weeds or control their growth and
successful, the introduced natural enemies become disrupt soil conditions suitable for the survival of some
established within large areas and effectively lower microorganisms and insects.
target pest populations for long periods of time with no
Exclusion is a mechanical control technique that
further need for intervention. The process is
consists of using barriers to prevent pests from getting
complicated because it is often difficult to locate the
into an area. Window screens, for example, exclude
native home of some pests, and natural enemies cannot
flies, mosquitoes, and other flying insects. Patching or
be released until it is proven that they will not become
sealing cracks, crevices, and other small openings in
pests themselves. Laws have been enacted that strictly
buildings can exclude insects, rodents, bats, birds, or
control the importation of all organisms, including
other pests. Fences and ditches make effective barriers
biological control agents, into the United States. Other
against many vertebrate pests. Wire or cloth mesh
countries have similar restrictions. Biological control
excludes birds from fruit trees. Sticky material painted
also involves the mass release of large numbers of
onto tree trunks, posts, wires, and other objects
natural enemies into fields, orchards, greenhouses, or
prevents crawling insects from crossing.
other locations to control specific pests. This method
usually does not have long-term results, so these Trapping
natural enemies must be released periodically. Several Traps physically catch pests within an area or building.
natural enemies are reared or cultured commercially. Several types of traps are commonly used. Some kill
Predatory mites are used to control plant-feeding spider animals that come in contact with them; others snare
mites. Parasitic wasps and lacewings are used to control animals so they can then be relocated or destroyed.
various insect pests. Nematodes and fungi are being Traps are either mechanical devices or sticky surfaces.
Cultural Control cause them to stop feeding, or prevent egg hatch or
The goal of cultural control is to alter the environment, development. Installing bright lights in attics sometimes
the condition of the host plant or site, or the behavior discourages bats from roosting there. Lowering the
of the pest to prevent or suppress an infestation. It
humidity of stored grains and other food products
disrupts the normal relationship between the pest and
reduces damage from molds and some insects.
the host plant or site and makes the pest less likely to
survive, grow, or reproduce. Cultural practices and Increasing air movement in glass or plastic houses often
sanitation are two examples of cultural control. helps to suppress fungal diseases from developing on
plants.
Cultural Practices Host Resistance or Genetic Control
Many cultural practices influence the survival of pests. Sometimes plants and animals can be bred or selected
In turf, mowing, irrigation, aeration, and fertilization are to resist specific pest problems. For example, particular
all important ways of producing healthy turf and livestock breeds are selected for physical characteristics
preventing pest buildup and damage. In agricultural that prevent attack by some pests or provide
crops, selection of crop plant varieties, timing of physiological resistance to disease or parasitic
planting and harvesting, irrigation management and organisms. Resistance also is enhanced by maintaining
timing, crop rotation, and use of trap crops help reduce the host’s health and providing for its nutritional needs.
populations of weeds, microorganisms, insects, mites, Certain plant varieties are naturally resistant to insects,
and other pests. Weeds also can be managed by pathogens, or nematodes. Many plants actually repel
mulching (with plastic, straw, shredded bark, or wood various types of pests, and some contain toxic
chips) and by using cover crops. substances. Plant resistance to insect pests can
sometimes be achieved by transferring genetic material
Sanitation from certain insect-destroying microorganisms to hybrid
Sanitation, or source reduction, involves eliminating seed. Genetic control has been widely used in the past
food, water, shelter, or other necessities important to and offers great promise for the future, especially when
the pest’s survival. In crop production, sanitation combined with new gene manipulation techniques.
includes such practices as removing weeds that harbor
pest insects or rodents, eliminating weed plants before Chemical Controls. These are pesticides that are either
they produce seed, destroying diseased plant material naturally derived or synthesized. Pesticides often play a
or crop residues, and keeping field borders or key role in pest management programs and frequently
surrounding areas free of pests and pest breeding sites. may be the only control method available. Major
Animal manure management is an effective sanitation benefits associated with the use of pesticides are their
practice used for preventing or reducing fly problems in effectiveness, the speed and ease of controlling pests,
poultry and livestock operations. In non-agricultural and, in many instances, their reasonable cost compared
areas, certain pests are controlled by draining standing with other control options. Usually pest damage stops
water. Closed garbage containers and frequent garbage or pests are destroyed within a few hours (for insects)
pickup eliminate food sources for flies, cockroaches, to a few days (for weeds) after application of a
and rodents; removing soil, trash, and other debris from pesticide. Using a fungicide may provide immediate,
around and under buildings reduces termite and fungal short-term protection against microorganisms. A
rot damage and prevents rodent nesting. pesticide is defined as any material that is applied to
plants, the soil, water, harvested crops, structures,
Physical/Environmental modification clothing and furnishings, or animals to kill, attract, repel,
Pests that occur in enclosed areas may sometimes be
or regulate or interrupt the growth and mating of pests,
suppressed by altering physical and environmental
or to regulate plant growth. Pesticides include a wide
conditions such as water, air movement, temperature,
assortment of chemicals with specialized names and
light, and humidity. Refrigeration, for example, protects
functions. They are commonly grouped according to the
stored food products, furs, and other items from insect
type of pest they control.
pests; lowered temperatures either kill the insects,
• avicides control pest birds. years. Others provide only short-term control,
• Bactericides control bacteria. sometimes lasting only a few hours.
• Disinfectants (antimicrobials) control microorganisms.
• Fungicides control fungi. Regulatory Pest Control
• Herbicides control weeds and other undesirable plants.
Some pest problems cannot be controlled
• Insecticides control insects and related arthropods.
• Miticides (acaricides) control mites. successfully at a local level. These problems involve
• Molluscicides control snails and slugs. pests that seriously endanger public health or are likely
• nematicides control nematodes (roundworms). to cause widespread damage to agricultural crops or
• Predacides control predatory vertabrates. animals, forests, or ornamental plants. Quarantine or
• Piscicides control pest fish. eradication programs directed by governmental
• Repellents repel insects, related invertebrates, birds, and agencies according to federal and state laws are used to
mammals. prevent the introduction and spread of such pests.
• Rodenticides control rodents.
• Defoliants cause leaves or foliage to drop from plants. •
Quarantine is a pest control process designed
Desiccants promote drying or loss of moisture from plant
to prevent entry of pests into pest-free areas. Some
tissues.
• Growth regulators are substances (other than fertilizers or states maintain inspection stations at all major entry
food) that alter the growth or development of a plant or points to intercept pests or materials that might harbor
animal. pests. Regulatory agencies monitor airports and ocean
ports. Quarantine also prevents movement of
Each group of pesticide includes several classes or designated pests within a state. Produce and other
families. For example, the classes of insecticides include, identified items being shipped from a quarantine area
among others, the organophosphates, organochlorines, must be fumigated to destroy pests before shipment.
carbamates, pyrethroids, botanicals, insecticidal soaps, Nursery stock, plant cuttings, and budding and grafting
and microbials. The pesticides within a particular class material are also regulated to prevent the spread of
have similar chemical structures or properties or share a pests.
common mode of action. The mode of action of a
pesticide is how the pesticide works. In other words, it Eradication is the total elimination of a pest
is what specific system(s) in the pest are affected by the from a designated area; often, these pests are under
pesticide. The various classes of chemicals work in quarantine restrictions. When eradication is required,
different ways and present different risks and problems. the geographical extent of pest infestation is
Pesticides also vary in their selectivity. determined and control measures are taken to
Fumigants, for example, are non-selective, controlling a eliminate this pest from the defined area. Procedures
wide variety of pests—fungi, insects, weeds, may include an areawide spray program, releasing
nematodes, etc. Some non-selective herbicides control sterile insects, using mechanical and cultural practices,
any plant given a sufficient dose. In contrast, selective and intensive monitoring for pests within and around
products control only certain species of pests or affect the borders of the infested area.
only a certain stage of pest development. For example, Government agencies are authorized to destroy
certain herbicides control broadleaf weeds while not weeds and plants that cause fire hazards, harbor
harming grasses, and ovicides kill only the eggs of harmful pathogens or animals, or are noxious to people
certain insects, mites, and related pests. or livestock in and around agricultural areas. Similar
Pesticides may move in various ways after they come in
authority applies to diseased or infected livestock or
contact with a host. Systemic pesticides are absorbed
through leaves or roots and then transported within the poultry and to weeds and nuisance plants in residential,
treated plant. Similarly, systemic insecticides can be commercial, and industrial areas. Mosquito abatement
eaten by or injected into livestock to control certain is an important pest control function undertaken to
pests. By contrast, contact pesticides are not absorbed protect public health. Under the authority of mosquito
by treated plants or animals. These pesticides must abatement laws, state agencies drain or treat standing
directly touch the pest or a site the pest frequents to be
water that provides breeding sites for mosquitoes.
effective.
EFFECTIVENESS OF PEST MANAGEMENT PROGRAMS
Pesticides also vary in their persistence, or how long
they remain active to control pests. Some residual Pesticides often play a significant role in pest
pesticides control pests for weeks, months, or even management programs. Their use requires certain
precautions be taken to avoid the development of through a pest population can occur much more rapidly
resistant pest populations. Although pest resistance can in pests that have many generations per year and many
occur, it does not cause every pesticide failure. Make offspring per generation, such as many insects, fungi,
sure that you have used the correct pesticide and the and rodents. Several pest management tactics help
correct dosage, and that you have applied the pesticide prevent or delay the occurrence of pesticide resistance.
according to label instructions. Sometimes a pesticide One approach involves the use of new or altered
application fails to control a pest because the pest was pesticides. Using new compounds with different modes
not identified correctly and the wrong pesticide was of action will lessen the likelihood of resistance
chosen. Other applications fail because the pesticide developing in a population. Unfortunately, new
was not applied at the correct time—the pest may not replacement products are often quite complex, difficult
have been in the area during the application, or it may to synthesize, and very costly to develop, and they have
have been in a life cycle stage or location where it was very specific modes of action, which can rapidly lead to
not susceptible to the pesticide. Also, remember that the development of resistant pest populations even
the pests that are present may be part of a new after very limited use in the field. No longer can we
infestation that developed long after the chemical was expect to respond to pesticide resistance by merely
applied. substituting one pesticide for another. Changing
pesticide use patterns is an important step in preventing
Even non-chemical pest management tactics resistance. When dosages are reduced, fewer pests are
become ineffective if the pest and the susceptible killed, so the pressure to develop resistant pest
stage(s) of its life cycle are not identified correctly. populations is decreased. Applying pesticides over
Successful pest management programs do not happen limited areas reduces the proportion of the total pest
by accident—they depend on careful observation, a population exposed to the chemical, thereby
thorough knowledge of the pest and the damage it maintaining a large pool of individuals still susceptible
causes, an understanding of all available pest control to the pesticide. This tactic has a tendency to delay the
options, and a caring, professional attitude. Pesticide development of a resistant population because
Resistance Pesticide resistance can be defined as the pesticide-susceptible individuals in the population
ability of an insect, fungus, weed, rodent, or other pest continue to interbreed with resistant ones, thus diluting
to tolerate a pesticide that once controlled it. the resistance in the population. Also, treating alternate
Resistance develops because intensive pesticide use kills generations of pests with pesticides that have different
the susceptible individuals in a population, leaving only modes of action decreases the selection pressure for
the resistant ones to reproduce. Initially, higher labeled resistance. Managing pesticide resistance is a very
rates and more frequent applications are needed to important aspect of integrated pest management.
control resistant pests. Eventually, however, the Monitor pest populations carefully and treat only when
pesticide will have little or no effect on the pest necessary, rather than treating on a calendar basis.
population (see Figure 1.4). Resistance may develop to Good pesticide application records are an important
only a single insecticide, fungicide, herbicide, or component of resistance management. Pesticides are
rodenticide. More often, however, pest populations more effectively managed when treatment history is
become resistant to all chemically related pesticides in a known. Resistance must be detected when it is at a very
class of compounds. It is also possible for a pest to low level and then controlled by using all available pest
develop resistance to pesticides in two or more classes management techniques to extend the useful life of our
of compounds with unlike modes of action. Continual current pesticides.
use of pesticides from the same chemical class, such as
all organophosphate or all pyrethroid insecticides, Resistance Management
increases the likelihood that resistance will develop in •  Use new or altered pesticides.
pest populations. Frequent applications and persistence •  Change pesticide use patterns.
•  Treat only when necessary.
of the chemical further increase the chances of
resistance occurring. Finally, the spread of resistance