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Natural selection- If some individuals in a population carry genes that allow them to better tolerate a
new, otherwise lethal set of conditions, then those individuals are more likely to survive and reproduce.
This process, whereby some individuals carrying alternative inherited traits survive and reproduce under
stressful conditions.
Ecological niche- Refers to all the components of the habitat with which an organism or population
interacts. An individual’s ecological niche includes the role it plays in the community as well as the
combination of conditions and resources that allow a viable population to exist
A description of an individual’s niche would include its source of energy, nutrition, how it affects other
organisms (predator, prey or competitor) and the extent to which it is capable of modifying the ecosystem.
The ecological niche may reveal insights into the pest’s role in the community The ecological niche of an
insect pest may also include various plant associations, some pests may move into different plants such
as weed hosts or switch to other foods during certain times of the year.
Habitat- The environment in which an individual or species population lives. Habitat includes the
biological and physical environment that surrounds an individual organism or population. EX: a
mosquito’s habitat includes water but also include surrounding plants and organisms which provide food
and shelter, cover or prey for predators or competitors
Population density- The number of individuals of a species in a defined area. Population density is
variable; that is, population size increases and decreases over time. There are factors, however, that
usually operate in an ecosystem to keep populations within certain boundaries. For instance, as
population density increases, there is likely to be increased competition for limited resources— such as
nutrients, water, and sunlight in the case of plants or food, water, and shelter for many animals—until the
population ceases to grow, declines, or migrates. Conversely, as population density decreases,
necessary resources may again become abundant, allowing the population to recover. Many other
factors, such as predators, disease, or climate, can impact population density.
Ecotype- a locally adapted population of a species that allows it to live in a specific habitat. Ecotypes are
genetically determined and evolve through natural selection. For instance, a hot weather ecotype of a
species may evolve in an area characterized by high temperatures that other populations of the same
species may not tolerate. Among plant pathogens, pathotypes could be considered as ecotypes.
Pathotypes are strains of a plant-pathogenic fungus adapted to particular cultivars of a host plant. New
ecotypes of pest species may allow the species to expand its range and become a more serious threat to
certain
managed systems. For instance, purple nut sedge, Cyperus rotundus, has been traditionally suppressed
in many areas of the world Grassland by flooding fields for lengthy periods, often in rice rotations;
however, recently, new ecotypes of purple nutsedge have evolved that tolerate flooding and have even
become a major problem in flooded rice fields in southeast Asia.
Species diversity- Measure of a number of species in an area and their relative abundance. Species
diversity is often higher in biologically controlled (natural) ecosystems and lower in physically controlled
(managed) ecosystems. Large increases in population size of individual species and more frequent
fluctuations between high and low population densities may be more likely in communities with relatively
low diversity.
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Distinguish between a population and a community of organismsA population is a group of individuals of the same species that occupies a distinct space and possesses
characteristics that are unique to the group. The genetic makeup of the population together with local
environmental and ecological factors determine the population’s success (how well it survives and how
fast it grows). Characteristics of local populations can evolve through natural selection. For instance,
certain populations of many invertebrates and some plant pathogens and weeds have developed
resistance to commonly used pesticides. Once resistance has developed, these populations can no
longer be controlled with those pesticides and alternative management strategies must be developed.
A community consists of all the populations of plants, animals, and microorganisms that share the same
habitat and interact directly or indirectly with one another. Communities can be of any size and are often
defined by the environment in which they occur or by the dominant species in the community. Not all
organisms in a community have an equal effect on the community. Generally, a relatively few species,
such as the large species of trees in a forest, exert a major controlling influence on the entire community.
Factors that impact population regulations
Population growth occurs when birth rates exceed death rates or immigration exceeds emigration.
Population size may be affected by physical factors such as weather, water availability, and nutrient
availability. Populations may also be biologically controlled by factors such as predators, competitors,
disease, or food availability. Factors that affect population density can be categorized as density
dependent or density independent. Density-independent factors affect populations regardless of
population density and include disturbances such as floods, drought, fire, other unpredictable
environmental conditions, and most pest control actions. In each case, a similar percentage of the
population is killed regardless of whether the density is high or low. Density-dependent factors have a
different effect when populations are high compared with when they are low. Competition for resources,
and predation, parasitism, and disease are examples of factors that can limit population growth in a
density-dependent way. For example, areas of high prey density attract certain predators and allow them
to more easily find prey, so that a higher portion of the population is killed by predation
than when numbers are low and prey are harder to find. Likewise, disease-causing pathogens spread
more readily in areas of high population density, increasing the mortality rate. Density-dependent factors
are important in regulating populations, and they help keep populations at equilibrium as opposed to the
often-catastrophic effects of density-independent factors (Figure 2-6). Sometimes density-dependent and
density-independent factors work together to help control a pest. For example, when hot, dry
temperatures occur when citrus red mite populations are high, virus epidemics often decimate the mite
populations. Similarly, fungal diseases of aphids are favored by warm and humid conditions but move
through populations and exert their greatest impact when aphids are abundant.
Describe how age distribution impacts growth rate of a population
Populations consist of individuals of different ages. The proportion of individuals in each age group
defines a population’s age distribution. Birth and death rates are important factors determining age
distribution. Immigration and emigration can also be sources of population
increase or decline. The proportion of individuals of different ages in the population can indicate whether
the population is expanding, declining, or remaining stable. Expanding populations
characteristically have a large percentage of young individuals, declining populations have a large
percentage of old individuals, and stable populations have a relatively even distribution among age
groups. For example, the population of a vertebrate pest, such as meadow voles, can expand rapidly in a
new environment due to high birth rates but then stabilize over time as population density rises and
mortality increases among its young due to factors such as predation or food shortages (Figure 2-4).
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Population fluctuations, however, are normal, and population stability can be rare, as in vole populations
in agricultural situations, where management is frequently necessary. Many of the organisms in managed
systems are short lived, with life cycles that are well synchronized with the culture of the crop. Often the
entire population begins the season at the same stage—for example, egg, overwintered larva, seed,
vegetative off shoot, or spore. For organisms that live only one season and have just one generation per
year, most individuals are about the age at the same time during the season.
Likewise, many annual weed species in a field will germinate at about the same time (winter or summer
annuals) when first irrigated, resulting in all newly germinated individuals being approximately the same
age. Even organisms with several generations per year, like codling moth, can maintain brood or cohort
effects where most individuals in the population are of similar age at any one time (Figure 2-5). These
generational broods can be important in timing management practices. Very rapidly reproducing species,
like aphids, which have many generations per season, tend to show fewer brood effects and have
individuals at different ages present at any time. In a population of perennial weed species or vertebrates,
several overlapping generations are also likely to be present.
Contrast density dependent and density independent limiting factors
Within an agroecosystem, each species exhibits a typical population level, often called its characteristic
abundance, as determined by its ecological niche. For instance, whereas it may be typical for an acre of
an orchard crop to have thousands of caterpillars, only a few raptors, such as hawks, could be supported.
Limiting factors such as food, shelter, or natural enemies enforce this characteristic abundance within
certain upper and lower levels, which fluctuate around a mean level called the equilibrium position. The
equilibrium position is maintained primarily by constraints set by the physical environment and
interactions with other
species. The most important factors involved in maintaining a population around its equilibrium position
density are density dependent factors, such as parasitism, competition, or predation, that exert more
pressure when populations are high and have a diminished influence at low population density.
List three types of population dispersal patterns
Dispersal. The movement of individuals or their offspring (e.g., seeds, spores, or
larvae) into or out of an area is called dispersal. Dispersal allows individuals to colonize new areas. Along
with birth rates and death rates, dispersal regulates populations. Dispersal also plays an important role in
the evolution of populations because it allows the mixing of genes between populations. Dispersal is
accomplished through immigration, emigration, or migration. Immigration is movement into a population.
When populations are at low densities, immigration accelerates population growth and in extreme cases
prevents extinction. Emigration is movement out of the population. When populations become extremely
abundant in a given area, emigration reduces population density and often helps in reestablishing an
equilibrium. Migration is the frequent movement into and out of a population area. Migration may involve
the mass movement of populations. Occupation of areas that are sometimes unfavorable is made
possible by seasonal and diurnal migration. Birds flying south for the winter is an example of seasonal
migration. Many pests migrate as well. For instance, grasshoppers and lygus bugs migrate from
uncultivated foothill areas to crop fields in the late spring
Describe how a community and the abiotic(non-living) environment function together as an
ecological system or ecosystem
Abiotic, or nonliving, factors in ecosystems influence the growth, development, and ability of organisms to
survive. They also influence the interactions between organisms. The abiotic components that most
commonly affect organisms in managed situations include minerals, soil, water, temperature, climate,
light, and gases.
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B. The ecosystem concept
Describe how the energy flows through an ecosystem
Organisms interact and depend on other organisms, the biotic components of the ecosystem, as well as
the abiotic (nonliving) components such as dead matter, minerals, water, and energy.
Energy flow drives the ecosystem, deter mining limits to the food supply and the production of all
biological resources. Light energy from the sun is captured by green plants and converted to chemical
energy. Energy is stored in plants as carbohydrates and used by the plant to support all functions (Figure
2-8). Other organisms use and convert this chemical energy to various forms through food chains. At
each step, some of the chemical energy is assimilated and used by the organism and the rest is released
in respiration and waste products. The goal of crop production is to maximize ecosystem energy into a
harvestable product; use of plant energy by pests and competition by weed pests are undesirable as both
take away from crop production.
Describe the role of photosynthesis in an ecosystem
The process by which green plants use energy from the sun to convert carbon dioxide and water into
carbohydrates is called photosynthesis (Figure 2-9). Nearly all plant growth depends on the capture of
solar energy, which occurs in the green plant parts containing chlorophyll. Chlorophyll molecules capture
sunlight and convert it into chemical energy. The importance of photosynthesis to an ecosystem is
paramount because, as primary producers, plants are the principal source of energy and organic material
for the ecosystem. A reduction in the photosynthetic capacity of the ecosystem will limit the survival of
other organisms.
Describe the biogeochemical cycle in an ecosystem
Cycles. Many mineral or inorganic elements are required for the growth and development of living
organisms. These inorganic elements and compounds, which include carbon, hydrogen,
oxygen, and nitrogen, circulate through the ecosystem from the nonliving to the living and back to the
nonliving parts of the biosphere. This circular path is known as a biogeochemical cycle. During this
process, some nutrients are returned immediately to the environment as quickly as they are removed.
Other nutrients are stored in the tissues of plants and animals, while still others are chemically bound or
stored in the soil surface for a long time before becoming available to living organisms. A slow and steady
exchange takes place between the easily available nutrients and the relatively unavailable nutrients. In a
typical biogeochemical cycle, plants take up nutrients from the soil and organize them into biologically
useful compounds. Many other organisms take the nutrients into their bodies by feeding on plants or
herbivores. Organisms of decomposition, such as some fungi, return the nutrients to their elemental state.
Air and water move the nutrients between the organic and inorganic components of the ecosystem. Each
of these factors is essential for the cyclic flow of nutrient to occur. There are two basic types of
biogeochemical cycles: gaseous and sedimentary. In gaseous cycles, such as the nitrogen cycle (Figure
2-11), the atmosphere acts as the nutrient reservoir. In sedimentary cycles, such as the phosphorus
cycle, the earth is the reservoir. A variety of biogeochemical cycles exist for the cycling of nutrients such
as nitrogen, hydrogen, phosphorus, carbon, and sulfur. Trace elements or micronutrients also enter
biogeochemical cycles, but plants and animals require them in much lower quantities.
List examples of abiotic compounds
The abiotic components that most commonly affect organisms in managed situations include minerals,
soil, water, temperature, climate, light, and gases.
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Describe a food chain
In reality, linear food chains are too simplistic to realistically describe true ecosystems. At every level of a
food chain, many organisms may feed on a single organism so that feeding and energy flow form
complex food webs. Yet all links in the food chain lead from producers to primary and secondary
consumers. Food webs in highly productive ecosystems are complex and support many species (Figure
2-16). Patterns of complexity in food webs are important to ensure survival. Being part of a complex food
web allows consumers to substitute food resources when one source is in short supply.
List common trophic levels in an ecosystem
The flow of energy in an ecosystem can be characterized in specific patterns. Energy flows from
producers (green plants) to primary consumers that feed on them, to the secondary consumers or
predators that in turn consume them, and all the way to the decomposers of dead organisms at the
bottom of the energy chain. The transfer of energy from one trophic level to the next is called the trophic
structure of the ecosystem and has an energy cost (loss during each transfer)
that typically limits the levels to four or five. The simplest way to analyze the flow of energy through an
ecosystem is to construct a food chain (Figure 2-15). At the base of every food chain is the autotroph, or
producer (green plants). Plant consumers, or herbivores, occupy the second level of the food chain, the
primary consumer level. Herbivore consumers, or carnivores, occupy the third level of the food chain, the
secondary consumer level (carnivores may include predatory or parasitic organisms). Carnivores that eat
other carnivores occupy the fourth level of the food chain, the tertiary consumer level. The final level of
the food chain consists of decomposers, primarily fungi, bacteria, and invertebrates that break down dead
matter into organic substances. Decomposers, in turn, have their own predators and are the basis of a
different food chain in the soil. Many organisms do not fit neatly into a single level of the food chain. The
food habits of some consumers can change with the season or during different stages in their life cycle.
Some consumers, such as the raccoon, are called omnivores because they feed on both plants and
animals. Organisms that feed on dead plant or animal matter
are called saprophytes, but some organisms that commonly feed on living organisms as predators,
parasites, or herbivores may also be capable of surviving as saprophytes when other food is scarce;
these organisms are called facultative saprophytes.
C. Managed ecosystems
Agroecosystems
An ecosystem managed for agricultural purposes.
Managed ecosystems
Every agricultural field, urban landscape, park, managed forest, rangeland, or roadside represents an
ecosystem that is managed in some way to benefit people. Some are man made, simplified ecosystems
that are intensely managed. Others, such as forest systems and rangeland, are more long-term
ecosystems that have been modified and managed to favor the growth of a few plant species. Agricultural
ecosystems, or agroecosystems, are predominantly monocultures. In a monoculture, the age and
genotype of crop plants are relatively uniform, and species diversity is limited. Complex food webs are
simplified because of the lack of diversity at the primary producer level. The autotrophic component
consists almost entirely of the crop plant. Weed species are undesirable and eliminated. Also, the
physical diversity of the system is much lower than in natural ecosystems. The uniformity of some
monoculture systems can encourage pest outbreaks. Disease epidemics or pest outbreaks can move
rapidly in a monoculture system. The establishment of a complex community of organisms,
in many monocultures, is often discouraged by management practices such as broadly
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toxic pesticides or removal of all weeds. However, in some IPM programs, managers try to increase
diversity to help manage pests by introducing biological control agents or intercropping to provide habitat
for natural enemies or as trap crops for pests.
In agroecosystems, inputs and outputs are manipulated by managers and depend
largely on supplemented sources of energy and nutrients (Figure 2-17). Productivity is
measured in terms of yield. High yields are maintained by inputs such as cultivation,
irrigation, fertilization, genetic selection, pest control, and the fuel used to run the
machinery that carry out these operations. However, unless carefully managed, excessive irrigation,
fertilization, or pest control can drive the cost of producing a crop higher than the yield can return.
Limiting factors of the agroecosystem
All organisms have basic requirements to live and thrive in a given situation. Crop plants have certain
light, soil moisture, fertility, and climatic requirements to ensure optimal growth. Likewise, the population
of other organisms in the ecosystem, such as pests, is
regulated partially by light, temperature, and water, as well as food sources, predators,
competitors, and other organisms. When one or more of these factors is in short supply or overabundant,
the growth and development of the affected organism can be
reduced, resulting in stress or death. Any of these factors is called a limitingfactor.
In managed ecosystems, people may employ practices to provide optimal conditions for
plant growth by maintaining limiting factors at appropriate levels. For instance, a limiting
factor in the growth of some young plants may be sunlight. Shade produced by larger weeds
limits the rate of growth. Addition of other growth requirements, such as water or nutrients, will not
increase growth rate until the sunlight deficiency is corrected. Weed control is aimed at ensuring that this
factor does not become limiting to the crop plants.
D. The ecology of pest problems
Equilibrium population density
Within an agroecosystem, each species exhibits a typical population level, often called its characteristic
abundance, as determined by its ecological niche. For instance, whereas it may be typical for an acre of
an orchard crop to have thousands of caterpillars, only a few raptors, such as hawks, could be supported.
Limiting factors such as food,
shelter, or natural enemies enforce this characteristic abundance within certain upper
and lower levels, which fluctuate around a mean level called the equilibrium position.
The equilibrium position is maintained primarily by constraints set by the physical
environment and interactions with other species. The most important factors involved in maintaining a
population around its equilibrium position density are density dependent factors, such as parasitism,
competition, or predation, that exert more pressure when populations are high and have a diminished
influence at low population density.
R and K strategists
Species that have high rates of reproduction and rapid growth are known as r strategists. These species
rapidly colonize new areas and thrive when competition is not severe. Characteristics of
r strategists include a high rate of reproduction, rapid dispersal, efficient host finding ability, and small
size. Many pest species are r strategists, including aphids, mites, and common weeds such as
barnyardgrass, starthistle, and chickweed. Most foliar pathogens are typical r strategists. Agroecosystems
typically remain dominated by r strategists as a result of repeated disturbances from management actions
such as cultivation, harvesting, planting, and pesti
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cide application. When competition for resources is high, species with better competitive abilities but
slower reproduction and growth rates may be more successful. Species that demon
strate these survival mechanisms are known as K strategists. Characteristics of K strategists include
larger size, longer life cycles, and higher survival rates of offspring but lower reproductive rates. Some
species have characteristics that place them somewhere
between typical r and K strategists. Fewer pest species are K strategists; examples
include some woody weeds, some root pathogens that slowly kill trees, and large
tree-boring beetles. Mature ecosystems with the greatest biodiversity are most likely to be dominated by
K strategists.
Biodiversity
Biodiversity is the number of different species of plants, animals, and microorganisms in an ecosystem.
The term can also refer to other levels of biological diversity, including
genetic variability in a species, diversity in communities, and the diversity of communities and ecosystems
in the biosphere. Biodiversity generally (but not always) is greater in natural, more mature ecosystems
than in younger, managed ones. Maintaining natural biodiversity is important not only to conserve the
diversity of species in nature but also to provide a resource for future agricultural crops and animals.
Compare and contrast preventative, suppressive and eradicative approaches to pest management
Preventive methods discourage damaging pest populations from developing and include planting weedand disease-free seed and growing varieties of plants that are resistant
to diseases or insects. Cultural controls such as cultivation to kill weedy plants before they go to seed or
choosing planting and harvesting dates unfavorable for the pest are techniques that prevent pest
establishment. Other preventive methods might include preplant soil disinfestation (such as fumigation,
heat treatment, or soil solarization),
removal of overwintering sites, and the selection of planting sites that are not already infested with pests
that attack the intended crop.
Suppressive pest control methods reduce existing pest populations to tolerable levels.
Most pest control actions fit into this category and include the release of biological control agents,
mowing, cultivating weeds, or in-season pesticide sprays. The management method chosen does not
usually eliminate pests but limits their damage or competition. Two or more suppressive methods are
often combined to enhance control.
Eradication strategies, in which no pests can be tolerated, are aimed at totally eliminating the pest from
a designated area. Eradication has the appeal of offering a complete solution and in special instances
may be a desirable strategy. Newly invading exotic pests posing a health or severe economic threat are
the usual targets of eradication programs. Coordination of eradication efforts is usually the responsibility
of government agencies. Examples of this approach to pest management are efforts directed at
eliminating the parasitic plant Japanese dodder from some areas of California and the Mediterranean fruit
fly and the oriental fruit
fly from southern California (Figure 3-1). For most pests, however, eradication is not feasible and is not
compatible with integrated pest management systems.
Factors to be considered in pest management decision making
Economics is a major factor in most pest management decisions. Pest populations can lower crop yield or
quality and impact the long-term health of perennial crops such as fruit trees, thereby reducing profits.
The cost of pest control activities, including
labor, equipment, and material, is a factor in each pest management decision. Human
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and environmental health hazards are costs that must also be taken into account. Other
factors important in pest management decision making are severity of the pest, impact
of the damage, effectiveness of the control, and the time delay before an action becomes
effective. These considerations are based on past records of pest occurrence and dam
age, trends in pest development, and the likelihood of future attacks. Successful pest
management decisions require information about the pest species—its biological characteristics,
distribution pattern and population density, impact on the managed ecosystem,
and the cost and likely effect of control.
Pest
An organism that interferes with the availability, quality, or value of a managed resource.
key pest
A pest that causes major damage in a crop on a regular basis unless controlled.
occasional pest
Occasional pests become intolerable only irregularly, often due to climate, environmental influences, or
as a result of human activities
secondary pest
activities. Secondary pest problems occur as a result of actions taken to control a key pest. For instance,
aphids and soft scale can become secondary pests when pesticides applied to control codling moths kill
their natural enemies. Some weed species may become secondary pests. Often these secondary pest
weeds are tolerant or resistant to the herbicides applied to control key weeds or were previously
suppressed by competition from the key weeds.
Recognize that pest species can exist at tolerable levels
for example, codling moth is a key pest because it often requires regular control efforts
to prevent economic damage to the crop. Treatments for codling moth can induce outbreaks or suppress
populations of other walnut pests. Occasional pests become intolerable only irregularly, often due to
climate, environmental influences, or as a result of human activities.
integrated pest management
An ecosystem-based pest management strategy that focuses on long-term prevention of pests or their
damage through a combination of techniques such as biological control, habitat manipulation,
modification of cultural
treatment threshold
The level of pest population at which a pesticide or other control measure is needed to prevent eventual
economic injury to the crop; also called economic threshold or action threshold.
host resistance
is a preventive pest management tool that takes advantage of the genetic attributes of certain plant
cultivars and allows the plants to resist or tolerate pest attack. Host resistance is one of the most
successful and ecologically sound pest management techniques and is used
widely, especially in the management of plant pathogens, nematode pests, and to a
more limited extent, arthropod pests. For example, there are tomato cultivars that are
resistant to root knot nematodes, Verticillium, Fusarium, tomato spotted wilt, and
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tobacco mosaic virus. Cultivars resistant or tolerant to downy mildew of lettuce and crucifers, celery
Fusarium yellows, white mold of beans, cucumber mosaic virus of
cucumber, root rots of peas, and tobacco mosaic virus of pepper are commonly used
in California. Likewise, there are many examples of resistant ornamental plants,
including roses resistant to powdery mildew and black spot, India hawthorn resistant to
entomosporium leaf spot, and crape myrtle resistant to powdery mildew.
biological control
Any activity of one species that reduces the adverse effect of other species
cultural control
The modification of normal crop or landscape management practices
to decrease pest establishment, reproduction, dispersal, survival,
or damage
mechanical control
Mechanical and physical controls are measures specifically taken to kill the pest directly or
to indirectly make the environment unsuitable for pest entry, dispersal, survival, or reproduction. Weak
links in the pest’s life cycle or specific behavioral patterns are often targeted. Cultivation for weed control
is an important mechanical weed management practice. Cultivation is sometimes also used in the
management of insects or pathogens, for example, burying plant litter that may harbor overwintering
insects or pathogen inoculum. Mechanical traps for vertebrates or cone traps for flies or wasps are also
examples of mechanical controls. Suction devices for insect control, such as bug vacuums, are another
example
pesticide resistance
The genetically acquired ability of an organism to survive a pesticide application at doses that once killed
most individuals of the species.
pest resurgence
The rapid rebound of a pest population after it has been controlled.
secondary pest outbreaks
A sudden increase in the population of a secondary pest (a pest that is normally at low or non-damaging
levels in the crop) caused by the destruction of its natural enemies by a nonselective pesticide applied to
control a primary pest.
Treatment threshold to economic injury level
Therefore, the critical issue in IPM programs is to define control action or treatment thresholds
(sometimes also called economic thresholds) that specify the population density at which control
measures must be applied to prevent crop loss or damage from going beyond acceptable levels. For
many pests, treatment must be applied well before unacceptable levels are reached
so population levels of the pest are not considered in the treatment decision. This is particularly true of
pathogens, which can rapidly develop into epidemics if environmental conditions are favorable. Treatment
thresholds depend not only on the growth and damage potential of the pest, but also on the efficacy of the
control procedures themselves. For instance, an
augmentative release of a natural enemy may be recommended at a lower population threshold than an
insecticide for the same pest because of the time required to establish biological control.
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Pest population levels and damage
Relationship of personal preferences on aesthetic injury levels on pest management decisions
For landscape pests, pest managers use the concept of aesthetic injury level, which is the level of pest
damage or pest populations the general public will tolerate. In mature
landscapes, many pests usually don’t cause economic damage. Pest control actions are
usually undertaken because the presence of the pest or the damage it causes is aesthetically displeasing.
Aesthetic tolerances vary among people and by the prominence of the
damaged plant. For instance, a certain level of damage may be tolerable in a background
plant but not tolerable on the same species planted at the entrance of a building. Some
people find the presence of any insect or weed intolerable while others are not bothered by them.
Defining an aesthetic injury level on which people can agree is difficult and
subjective. Management decisions are based on the attitudes of the PCA, the public, or
the client, as well as potential pest problems. An effective education program can often
increase the public’s tolerance for pest presence, thereby increasing aesthetic tolerance levels.
Management options available in integrated pest management
their disposal. Some of these, like crop rotation, host resistance, and habitat modification, are used in the
preventive mode. Other tools, such as certain pesticides, cultivating, or mowing weeds, are used primarily
to curtail pest populations that are approaching damaging levels. Many tools can be used both to prevent
damage and to control
Populations. Most pest control tools do not eliminate all pest individuals, only a percentage of the
population. Many are effective against one stage but ineffective against another stage. Some biologically
based or less toxic pesticides may control only part of a pest population, but this may be all that is needed
to keep a pest suppressed just enough to allow other mortality factors like natural controls to reduce the
population to a tolerable level. Some pest management tools may affect several different pests. Weed
control, for
example, may also result in fewer vertebrate pests. The pest manager must always
keep in mind the effect of any management practices on other pest organisms. Most
management tools fit into one of four major categories: biological, cultural, mechanical and physical, and
chemical.
Recognize the importance of natural enemies to IPM
Biological control agents are present in almost all ecosystems, even on the most intensely managed
farms. Many organisms are not considered pests simply because naturally
occurring biological competition in fields, orchards, and landscapes keep them in check
most of the time. These natural enemies are often at very low levels and may not be eas
ily observed; however, without them, many pests would increase to destructive levels and
become pests. A basic tenet of integrated pest management is to take advantage of free, naturally
occurring biological control whenever possible. In IPM, efforts are made to restore, enhance, or mimic the
biological control that occurs in natural situations.
List factors of the physical environment that impact pest populations
The physical environment sets limits on the functioning of the ecosystem and every species in
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it. Available heat limits the rate of growth as well as species survival. Water limits the growth of plants and
has a major impact on outbreaks of disease. Soil type influences water-holding capacity as well as
nutrition. The intensity of sunlight can be a limiting factor in photosynthesis.
Describe the role of water management on crop biology/pests
Too much or too little water can directly damage plants and cause changes that make the plant more
susceptible to pests or pest damage. For instance, overwatering is a major contributor to the development
of root and crown diseases such as those caused by Phytophthora or Pythium. On the other hand,
drought stress and insufficient water can increase shoot and branch dieback, providing an attractive
environment for other pathogens such as Cytospora canker or Botryosphaeria canker on many
ornamental trees. Tools such as tensiometers and evapotranspiration monitoring are available to assist in
determining a plant’s need for water. The type of irrigation can also contribute to pest infestations.
Overhead irrigation systems increase humidity and leaf wetness, which allow bacteria and fungal spores
of certain pathogens to spread and infect.
Recognize the importance of soil on crop biology/pests
Soil is the anchoring medium for plants and weeds; it supplies nutrients and water for both. It is a
reservoir containing many organisms, including microorganisms and invertebrates that aid in the
regulation of plant nutrient uptake, organic matter decomposition, soil fertility, and water retention.
Describe how soil type can impact success of chemical and cultural pest control
Soil characteristics can have a significant influence on weeds, soil pathogens, insects, and nematodes,
as well as on the feasibility of management practices. Soils high in clay or silt become extremely cloddy
and compacted when tilled in wet conditions. Coarse-textured soils that are low in organic matter have
low buffering or adsorptive capacity, which can increase herbicide activity. Soils too high in organic
matter, however, bind many soil-applied herbicides tightly, and inadequate herbicide activity occurs.
Plants grown in soils with high levels of nitrogen may be more prone to pests such as fire blight in pome
fruit or increased aphid populations.
Describe the importance of crop biology and pest biology to IPM.
In a managed system, the PCA must know the potential for damage by the specific insect, pathogen,
weed, or vertebrate pest and the options available to manage it. Plants are susceptible to most pests only
at certain times. Knowing the vulnerable stages of the plant and the pest stages that cause damage sets
the parameters for effective monitoring and treatment. The practices that enhance the growth and
development of the plant or crop are often advantageous for the pest species as well. Many insects and
pathogens thrive best when high rates of nitrogen application and irrigation stimulate lush new plant
growth. The weeds that compete most successfully with the host for light, water, and nutrients are often
those that emerge before the crop with the first rain or irrigation. Certain characteristics are common to
many successful pest species. Generally speaking, arthropod, plant, and pathogen species that become
pests possess strong dispersal abilities, and their populations increase rapidly (they are r-strategists, as
discussed in Chapter 2). Additionally, arthropod and pathogen pest species often have strong host-finding
abilities or a life cycle closely tied to that of the host. Population
regulating mechanisms such as biological control agents, competitors, or limits to
food supply, may be absent or reduced when pests become a problem. Pests have, in most cases,
adapted to the host’s environment and are able to exploit these conditions to the disadvantage of the
host.
EX: species. Fallowing disrupts the life cycle of certain disease organisms and nematode species. Crop
rotation can be effective against many soil pathogens, nematodes, vertebrates, and certain weed species.
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Removal of basal leaves from grapevines makes the environment less favorable for Botrytis bunch rot
fungi and leafhoppers. Overhead sprinklers can reduce mites but may increase some diseases.
Recognize how weed species composition can change due to repeated herbicide
Pest populations develop resistance to pesticides through genetic selection. (A) Certain
individuals in a pest population are less susceptible to a pesticide spray than other individu
als. (B) These less-susceptible pests are more likely to survive an application and to produce
less-susceptible progeny. (C) After repeated applications, the pest population consists pri
marily of resistant or less-susceptible individuals, and applying the same material or other
chemicals with the same mode of action is no longer effective.
Why use IPM
Integrated pest management combines a variety of cultural, biological, mechanical, and chemical controls
to optimize effectiveness and reduce the problems that can result from over reliance on one tactic. Even
more importantly, by incorporating information developed from research and field monitoring, IPM allows
more reliable decisions to be made, thus improving effectiveness of control actions.
Identify the characteristics of a successful pest
Successful pests often have strong competitive abilities and the capacity to reproduce rapidly over a short
time span or under special conditions. They have the ability to adapt to uncertain and variable
environments and have strong dispersal and host-finding capabilities.
Describe the importance of knowing a pest’s life cycle in an IPM system.
Misidentification of pests can contribute to the failure of pest control measures. Many pests look similar,
and some can easily be confused with beneficial or innocuous
organisms (Figure 4-1).Frequently, damage symptoms are incorrectly associated with an
organism that happens to be present at the time the symptoms are observed when, in
fact, that organism is not causing the problem. The pest that actually caused the damage may have left
the site or may be hard to detect, such as rodents that damage a tree trunk and then leave or a plant
pathogen confined within the root system and thus unable to be seen above ground on leaves or stems.
Recognize the levels in classification systems.
Phylum, class, order, family, genus, species
Knowing common and scientific names
It is also important for PCAs to be aware of common names of pest organisms. These are often the
names that growers or other clients use and are the pest names normally referred
to on pesticide labels. As indicated earlier, many pest species may be called by several different common
names, causing confusion. In addition, common names do not provide any information about the
relationship of one organism to another; knowing that species are closely (or distantly) related can be
useful in making pest management decisions. For example, the common names of johnsongrass,
sudangrass, and grain sorghum provide no clues as to the relationships of these three plants, but their
scientific names, Sorghum halepense, Sorghum sudanense, and Sorghumbicolor, immediately indicate
that they are closely related species in the genus Sorghum. Good sources of common and scientific
names for pest species can be found in the
“Resources” section.
Describe the importance of proper pest identification when selecting control strategies
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Identify the drawbacks of relying only on symptom identification for pest identification
Misidentification of pests can contribute to the failure of pest control measures. Many pests look similar,
and some can easily be confused with beneficial or innocuous
organisms (Figure 4-1).Frequently, damage symptoms are incorrectly associated with an
organism that happens to be present at the time the symptoms are observed when, in
fact, that organism is not causing the problem. The pest that actually caused the damage may have left
the site or may be hard to detect, such as rodents that damage a tree trunk and then leave or a plant
pathogen confined within the root system and thus unable to be seen above ground on leaves or stems.
Describe the importance of lab analysis in plant pathogen identification.
Although simple keys and photo identification guides that show pests and damage symptoms are a great
asset in the field, some times accurate identification can be made
only by trained experts, in some cases using special techniques and equipment. For
instance, some microbial pathogens require special laboratory testing for identification,
including incubation at specific temperatures to induce growth, use of selective
nutrient media, and examination under electron microscopes. Useful molecular tests,
such as enzyme-linked immunosorbentassay (ELISA) or polymerase chain reaction (PCR),
Distinguish the following invertebrate class
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Invertebrate
Invertebrates are animals without backbones. They include nematodes and segmented or true worms,
snails and slugs, and the arthropods, which include insects, spiders, mites, crustaceans, and their
relatives. Many invertebrates are classified as pests. Some transmit pathogens to people, animals, or
plants. A large number of invertebrates feed on plants. Some are considered nuisance or aesthetic pests.
Others are predaceous and beneficial.
Arthropod
Arthropods, phylum Arthropoda, are organisms with an external skeleton andjointed body parts. The
arthropod group includes six classes with members that are significant pests (Table 4-1) as well as
several minor classes. Insects are by far the most abundant
and diversified class of arthropods, with 31 different orders. Spiders, ticks, and mites
belong to the next-largest class, the arachnids. Other major arthropod classes are the crustaceans
(including sowbugs and pill bugs), the centipedes, and the millipedes. Symphyla is a minor class of
arthropods, but it includes the symphylans, which can be of some economic importance as pests.
Molt
Stages of development of a typical moth or butterfly, showing complete meta- Chrysalid or pupa, Adult
male morphosis. Most moths and butterflies go through four or five molts during the caterpillar stage.
Instar
The period between one molt and the next is known as an instar. Immature arthropods pass through
several instars before becoming adults.
Metamorphosis
ments. Most arthropods hatch from eggs into immatures that increase in size by molting or shedding their
outer body covering (exoskeleton) and growing a new, larger one. Often they modify their shape with
each successive molt, a process known as metamorphosis
Exoskeleton
outer body covering for an insect
Nymphs
Other insects, such as grasshoppers, aphids, and true bugs, go through gradual or incomplete
metamorphosis and do not have a pupal stage (Figure 4-14). Their immatures are called nymphs; they
differ from adults primarily in their size and absence of wings. Adults and immatures of these insects have
the same food habits.
Larva
The development of mites, spiders, and other arthropods is similar to the gradual
metamorphosis of insects. For instance, mites hatch from eggs and pass through several immature
stages before becoming adults; the stage that hatches out of the egg is normally called the larva (Figure
4-15). Later-stage nymphs look similar to adult
mites. Immature mites and spiders have feeding habits similar to adults of the same species.
Pupa
an insect in its inactive immature form between larva and adult, e.g., a chrysalis
Major invertebrate groups that are pests
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Invertebrates are animals without backbones.They include nematodes and segmented or true worms,
snails and slugs, and the arthropods, which include insects, spiders, mites, crustaceans, and their
relatives. Many invertebrates are classified as pests. Some transmit pathogens to people, animals, or
plants. A large number of invertebrates feed on plants. Some are considered nuisance or aesthetic pests.
Others are predaceous and beneficial.
Body parts and mouth parts on an insect
Body parts of mites
Body parts of spiders
Compare/contrast gradual and complete metamorphosis
Some species of insects undergo major morphological or structural changes between the immature
stages and adulthood. This transformation occurs within a nonfeeding pupal stage; these insects are said
to have complete metamorphosis (Figure 4-13). Immatures in these groups are called larvae and, in
many cases, have different feeding habits from adults, so that only either the larval or adult stage causes
damage. Examples of insects with complete metamorphosis include flies, wasps, moths, butterflies, and
beetles. Other insects, such as grasshoppers, aphids, and true bugs, go through gradual or incomplete
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metamorphosis and do not have a pupal stage (Figure 4-14). Their immatures are called nymphs; they
differ from adults primarily in their size and absence of wings. Adults and immatures of these insects have
the same food habits. The development of mites, spiders, and other arthropods is similar to the gradual
metamorphosis of insects. For instance, mites hatch from eggs and pass through several immature
stages before becoming adults; the stage that hatches out of the egg is normally called the larva (Figure
4-15). Later-stage nymphs look similar to adult mites. Immature mites and spiders have feeding habits
similar to adults of the same species.
Complete – has four distinct life cycle stages: egg, larva, pupa, and adult. Incomplete/gradual – only has
three life cycle stages: egg, nymph, and adult.
Life cycle of a moth
complete – egg–larva— pupa, and adult
Non-feeding pupa/pupal stage
Life cycle of aphid, stink bug and spider mite
Gradual – egg, nymph, and adult
Identify the importance of recognizing the eggs of insects and mites
The eggs of arthropods vary in size, shape, color, attachment, arrangement, and where they are laid
(Figure 4-16). Eggs are usually laid in a location where the young will have an immediate food source
upon hatching. Learn to identify the eggs and their typical location for pest and beneficial species. Eggs
can be used to detect a pest’s presence or forecast a pest’s destructive stage. For instance, egg traps are
used to monitor the egg-laying activities of the navel orangeworm, Amyelois transitella. Leaf samples are
used to monitor the egg laying of the tomato fruitworm, Helicoverpa zea, on processing tomatoes.
Identify types of damage insects cause to plants
Arthropods cause damage in many ways. On plant crops or ornamentals, they may chew twigs, leaves, or
fruit; suck sap; bore into branches, trunks, or fruit; chew or suck roots; lay eggs in plant tissues; or
disseminate disease organisms. Some insects are pests of structures or stored foods. Other arthropods,
such as flies, cockroaches, and ants, are nuisance pests or indicators of unsanitary conditions. Chewing
damage guides the investigator to insect orders with chewing mouthparts, such as beetles, the larvae of
butterflies or moths, orthopterans such as grasshoppers, and earwigs. For instance, in lettuce, ragged
holes in leaves, holes in the heads, and heads and leaves contaminated with frass are types of damage
associated with various caterpillars, including the cabbage looper (Trichoplusia ni) the alfalfa looper
(Autographa californica), the imported cabbageworm (Pieris rapae), or other leaf-feeding caterpillars. To
confirm the culprit, search the plants for caterpillars, eggs, pupae, or moths. Stippling or yellowing
damage on leaves, fruit, or twigs; leaf curling; deformed fruit; wilting; or the general decline of the whole
plant are damage symptoms associated with mites and piercing-sucking insects such as aphids, scale
insects, and true bugs. These symptoms could be the result of plant pathogens as well, so once damage
is evident, further monitoring will be needed to establish the identity of the pest organism.
Some of the most difficult pests to control are internal feeders such as borers, leafminers, gall insects, or
the larval stages of insects that develop inside fruits, nuts, or seeds. Bark beetles, an example of boring
insects, are considered among the most destructive insect pests of California forests. Pitch tubes and
sawdust like frass are indications of bark beetle damage. Adult bark beetles lay eggs in tunnels etched
between the bark and wood. The larvae feed on the inner bark and phloem and form branching tunnels or
galleries, causing further damage to the tree. Leafminers lay their eggs between the upper and lower
epidermis of a leaf. Off-color patches, sinuous trails, or holes in leaves indicate damage from leafminers.
Insects whose larvae feed in fruits or nuts are among the most economically damaging pests. Examples
include the codling moth, apple maggot, and the cotton boll weevil. This group typically lays its eggs on or
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just under the flesh, damaging fruit with stings and deep entries. Larvae hatch and bore farther into the
fruit, often tunneling into its core. Small piles of frass on the side of the fruit indicate an infestation. Root
feeders damage roots, limiting the plant’s ability to take up water and nutrients. Wilting and declining
plants are typical symptoms of root feeder damage. Grape phylloxera, Daktulosphaira vitifoliae, is an
example of an insect pest that damages the host by feeding on the root system. Grape phylloxera feed
either on growing rootlets, which then swell and turn yellowish, or on mature hardened roots, where the
swellings are often hard to see. Necrotic spots (areas of dead tissue) develop at the feeding sites on the
roots.
Identify the phylum of snails and slugs
phylum Mollusca, class Gastropoda
Describe how nematodes injure plants
Plants infected with root nematodes can exhibit damage symptoms on upper portions of the plant as well
as on the root. Symptoms such as stunting, chlorosis, wilting, curling and twisting of leaves and stems,
delayed or uneven maturation of crops, and fruit drop
can be associated with nematodes and with many other pests as well. Nematodes inject
saliva into the plant, which induces much of the distortion of plants. Root symptoms
produced by various nematodes include galls (Figure 4-24), swelling, stubby roots, lesions, and stunting.
These symptoms are indicative of nematode presence but are not by themselves diagnostic. An expert
should confirm nematode presence. Some nematodes develop an association with pathogens to develop
a nematode-disease complex. For instance, Fusarium wilt is more severe in cotton when nematodes are
present. Nematode vectors transmit several plant viruses, including tomato ring spot and grapevine
fanleaf.
Life cycle of plant parasitic nematode
Six distinct stages: an egg, four juvenile, and an adult stage. Molts b/w each juvenile and adult stage. No
metamorphosis.
Describe some above ground and root symptoms that can be associated with nematode damage
Above ground- stunting, chlorosis, wilting, curling, and twisting leaves and stems; delayed fruit maturity.
Roots – galls, swelling, stubby roots, and stunting
Distinguish ectoparasitic nematodes from endoparasitic nematodes
Migratory ectoparasitic species feed on root surfaces without becoming attached and are free living
throughout their life.
Migratory endoparasitic species move about freely but enter the plant during certain life stages and feed
from within
List types of vertebrates that can be pests.
common examples of vertebrate pests include commensal rats and mice, voles, bats, skunks, muskrats,
possums, rabbits, beaver, ground squirrels, moles, pocket gophers, coyote, deer, horned larks, crows,
and starlings.
Describe how the following signs can be used to help identify vertebrate pests:
Identification of vertebrate pest species can be relatively easy if the species doing the damage is
observed, but in most situations, this does not occur: damage is usually observed when the culprit is
17
nowhere in sight. Fortunately, vertebrate pests typically leave behind signs such as tracks, tooth marks,
droppings, dens, burrows, and trails. These signs coupled with a familiarity of the habits of vertebrates
can aid in identifying the species. Identifying the pest that is responsible for the damage can be difficult at
times because different animals can attack the same parts of the plant and cause similar types of
damage. For example, gophers and moles usually damage turf; root damage on fruit trees can be the
result of gophers or voles. Trunk damage can be attributed to voles, ground squirrels, or rabbits; birds,
rats, ground squirrels, and voles can feed on fruits (Figure 4-26) or leafy crops. Although typical signs can
be associated with vertebrate pest damage on many crops, the signs alone are not conclusive. An
integrated pest management program for vertebrate pests may incorporate many tools, including habitat
modification, trapping, poison baiting, fumigation, exclusionary devices, repellents, and frightening
devices. Most tools are more effective when populations are low, so regular monitoring is critical.
Distinguish monocots from dicots
Monocots produce only a single grasslike leaf in the seedling. Leaves typically have parallel veins that run
the length of their axis and flower parts in threes or multiples of three. Monocot weed species can be
found in two major families: grasses (Poaceae) and sedges (Cyperaceae). Sedges can easily be
distinguished from grasses. The stems of sedges are triangular in cross section, and their leaves are
arranged in threes at the base instead of twos as in the case of grasses. Important identifying features for
grasses are presence or absence of ligules or auricles in the collar region, where the leaf sheathjoins the
leaf blade, and flower structures such as awns and glumes in mature plants. Figure 4-27 illustrates some
of the structures used to identify grasses.
Dicots, commonly called broadleaves, are plants whose seedlings produce two cotyledons. Leaves of
dicots usually have netlike veins and flower parts usually in fours, fives, or multiples thereof. Dicots
commonly have a main taproot. Table 4-4 lists some common dicot weed families and some of their
identifying characteristics.
List major plant parts used to identify mature broadleaf weeds
plants whose seedlings produce two cotyledons. Leaves of dicots usually have netlike veins and flower
parts usually in fours, fives, or multiples thereof. Dicots commonly have a main taproot. Table 4-4 lists
some common dicot weed families and some of their identifying characteristics.
Recognize the key features used to identify:
Grass seedlings:
Broadleaf seedlings:
Life cycle of annual weeds
Annual weeds grow, reproduce, and die within one growing season. They sprout
from seed, mature, and produce seed for the next generation during this period. Annuals reproduce by
seed only. Depending on the time of year that they
begin growth, annuals are divided into two groups, summer annuals and winter annuals.
Summer annuals germinate in the spring; they flower and produce seed in mid to late
summer and die in the fall. Some common summer annuals include pigweed, punc
turevine, barnyardgrass, and yellow foxtail. Winter annuals germinate from late summer
to early winter, but they may not grow very much until the temperature warms toward the end of winter.
They flower and produce seed in mid to late spring and die in the early summer. Mustard, wild oats,
annual bluegrass, and filaree are examples of winter
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annuals. The designation of species as summer or winter annuals is not always clear cut. In cooler areas,
some winter annuals may also germinate and grow in summer.
Life cycle of biennial weeds
Biennials are plants that usually require two growing seasons to complete their
life cycle. Seeds germinate in the spring, summer, or fall of the first year. Biennials
overwinter as vegetative growth, generally in a rosette form, often with thick storage roots. Flower stalks
and seed are produced after the plant shoot tips have been exposed to cold. After producing seed,
biennials die in the fall of the second year. Poison hemlock, wild carrot, common mullein, and scotch
thistle are examples of biennial weeds.
Life cycle of perennial weeds
Perennials produce vegetative structures that allow them to live for 3 years or longer;
some species live indefinitely. Many perennials lose their leaves or die back entirely dur
ing the winter but regrow each spring from roots or underground storage organs such
as tubers, bulbs, rhizomes, or creeping roots or aboveground stolons (Figure 4-31). These plants are
herbaceous perennials. Most can also reproduce by seed. Many weedy perennials may be introduced as
seeds but invade new areas or spread via their vegetative organs. Examples of perennial weeds include
yellow nutsedge, johnsongrass, field bindweed, and bermudagrass. Woody plants such as trees and
shrubs are perennial and under certain circumstances are considered weeds. Examples of woody plants
that are often treated as weeds include poison oak, saltcedar, sagebrush, blackberries, alders, and
numerous others.
Describe the different vegetative reproductive structures of perennial weeds:
Perennial weeds that produce seed vegetative reproductive structures, such as
rhizomes, stolons, or tubers, have an even greater chance for survival. Perennial weeds store food in
their reproductive structures for overwintering, and on some species, buds become hardened and
dormant, ensuring survival in adverse conditions. Reproductive structures produce new shoots and when
broken off readily establish as new plants; cutting reproductive structures at certain times of the life cycle
may stimulate
the production of more plants. In addition, weeds growing from vegetative reproductive structures have
more stored energy and can establish more quickly than plants developing from seed
Describe how differing weed germination requirements affect management decisions.
The total number of weed seeds surviving in the soil or on the soil surface of an area
is called the weed seed bank. Thousands of seeds can be found in even a cubic foot of
agricultural soil, and many of these seeds may have been produced one or more years
previously. It is a good idea to assess the seed bank by taking soil samples to determine the type of weed
seeds and their abundance in a field. Soil samples can be watered to induce germination to identify
weeds. The seed bank can help growers and pest managers make predictions about future weed
problems and future management needs.
List the characteristics that make weeds successful competitors.
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Features including abundant seed production, rapid population establishment, seed dormancy, long-term
survival of buried seed (the seed bank), adaptations for seed
dispersal, the presence of vegetative reproductive structures, and the ability to invade sites disturbed by
people have ensured their survival and dominance. Weeds are competitive, persistent, and pernicious.
Weeds compete with other plants for light, water, and nutrients. Most weed species are successful at
germinating early and capturing more of the available nutrients. Rapid root and shoot development gives
the weed a distinct advantage by shading out desirable plants.
List the mechanisms by which weed seeds are disseminated
Weeds disperse in a variety of ways. Weed seeds may be blown around in wind, washed away in water,
or transported by animals that have fed on them. Human activities are an important means of dispersal in
managed systems. Weed seeds and other reproductive structures are carried in and out of fields on
contaminated equipment, in soil, and by attaching to workers’ clothing.
Differentiate between parasitic and nonparasitic (abiotic) diseases.
Diseases may also be caused by abiotic, or nonliving, factors. To properly resolve disease problems, it is
important to distinguish between those that are caused by pathogens and similar disorders and those that
are caused by noninfectious abiotic factors.
Disease triangle
For a pathogen to attack a plant, the plant and pathogen must come in contact with one
another and interact. Plant and pathogen are often present and in contact but disease does not develop,
either because the host is resistant to attack or the pathogen is unable to attack due to unfavorable
environmental conditions for disease development. These three components—host plant, causal agent,
and a conducive environment—are known as the disease triangle (Figure 4-33). One side of the triangle
represents each component. If any of the sides is absent or unfavorable, the disease will not develop. It is
essential to understand that a pathogen and the disease it causes are not synonymous. The pathogen
may be present, but there may be no disease if either of the other two sides of the triangle is not present.
The disease triangle. All sides of the triangle must be present for disease to occur. The disease becomes
more severe as
conditions on each side become more favorable.
Difference between pathogen and disease
Microorganisms that cause disease are commonly called pathogens. Fungi, bacteria, and viruses are the
most common pathogen groups causing disease in plants.
Difference between signs and symptoms
The symptoms of a disease refer to changes in the appearance of the infected plant, such as the necrotic,
sunken, ulcerlike lesions of an anthracnose infection. The signs of a disease, on the other hand, are
structures that the pathogen may produce on the surface of the host, such as mycelia, sclerotia,
sporophores, fruiting bodies, and spores
Thus, the white cottony mycelia and hard black clusters of dormant sclerotia found on
the lower stem of lettuce plants are signs of the Sclerotinia fungus; symptoms of Sclerotinia diseases
include wilting of the lower leaves and limpness of the entire plant.
The importance of identifying the causal agent of disease symptom
Field identification of disease symptoms caused by fungi can often help determine
20
the species responsible for the damage. Host indexes and other publications often list the pathogens that
are known to affect specific hosts. Although lists may be a good starting point in linking host symptoms to
a causal agent, the species responsible must be identified accurately before a control is recommended;
when in doubt, enlist the assistance of an expert.
Inoculation
Inoculation occurs when inoculum, the form of the pathogen that initiates infection,
comes into contact with a susceptible plant. In fungi, inoculum can be spores, sclerotia, or mycelia.
Bacteria, phytoplasmas, viruses, and viroids do not produce specialized structures for survival or
dissemination and must gain entry to a host as individual entities
Penetration
Pathogens enter the host by direct penetration through natural openings or
through wounds. Most bacteria enter plants through natural openings, such as stomata,
lenticels, nectaries, or through wounds. Viruses, viroids, and phytoplasmas enter
through wounds, through feeding by vectors or, in perennial plants, through grafts. Fungi commonly
penetrate directly through intact plant surfaces, although some enter through wounds to the plant.
Identify the importance of the overwintering stage of a pathogen on pest control strategies
Describe the impact of insects as vectors of disease
Insect vectors also provide an important overwintering mechanism for viruses. Viruses can enter plants
only through wounds. They are dispersed mechanically from plant to plant through vegetative
propagation, sap, seeds, and pollen or by vectors. Vectors of
one or more plant viruses include aphids, leafhoppers, whiteflies, beetles, thrips, mites, nematodes, fungi,
and dodders. Vectors are specific to certain viruses and hosts.
Describe the overwintering/oversummering mechanisms for:
Fungi – overwinter as mycelia or spores in or on infected tissue. Seeds, wood, debris
Bacteria – Do not overwinter as spores, but as saprophytically in plant debris. Survive mostly within plant
hosts as parasites.
Virus – Cannot overwinter outside of a plant, living contaminated volunteer plants can be important
overwintering sites.
List the mechanisms of dispersion for:
Fungi – Usually spread by humans, animals, or insects. Few can spread by rhizomorphs in the soil.
Spores spread by air-currents.
Bacteria – Usually by flowing water or rainwater, by moisture, and by various management practices. By
insects and seeds, cuttings, or transplants.
Virus – Enter through wounds, veg. propagation, sap, seeds, and pollen or by vectors.
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Explain how physical factors such as variations in temperature, nutrition, and water stress can
affect the degree of host plant resistance.
Although extremely valuable, the use of pest-resistant plant cultivars is not fool
proof. Occasionally a resistant plant can become more susceptible to pest pressure as a reaction to
physical stress such as variations in moisture, evaporation, plant and soil
nutrition, and temperature. For instance, Lahontan cultivars of alfalfa are much more
susceptible to stem nematode at 25°C (77°F) than at 15°C (59°F). An even more serious concern is the
potential for development of biotypes or physiological races of pests that can overcome the factors that
provide the basis for host resistance. Such races may develop as a reaction to the severe selection
pressure exerted by a resistant crop cultivar. Integrating the use of resistant cultivars with other
management tools such as sanitation, crop rotation, or certified seed can help prolong the useful life of a
resistant cultivar.
Tolerance
Tolerant plants are able to endure the presence of a pest with little or no long-term damage; however,
tolerant varieties sometimes support populations of a pest that can infest subsequent susceptible crops
True resistance
Plants that support few or no pest individuals that infest other varieties; as opposed to tolerance.
Apparent resistance
involves plants that fail to become infected with a pathogen because all the requirements for infection or
disease development (e.g., environmental conditions, susceptible host stage and quality, or pathogen
inoculum ) were not present. These same plants, planted under different conditions, could well be
susceptible to the disease
Hybrid
Hybrids are the offspring of a cross of two different purebred (homozygous) lines. The heterozygous
offspring (F-1) often combine the superior characters of the two lines and also increase the vigor of the
crop (hybrid vigor)
Transgenic
Transgenic pest-resistant cultivars result from the transfer of desirable traits from one
organism to another. In classical breeding programs, only closely related species can
be crossbred. Using transgenic techniques, plant breeders can transfer the genetic material from
completely unrelated organisms.
Scion
The scion is a shoot or bud that is grafted on to a root stock to develop into the trunk and branches of the
tree or vine3). Scion choice determines the harvested crop variety, pest resistance above the graft, and
many other production and market considerations.
Rootstock
Rootstocks are primarily chosen by growers to control tree vigor and improve fruit
or nut size and quality, cold hardiness, and adaptability to climate and soil conditions.
22
Resistance or tolerance of rootstocks to insects, diseases, nematodes, and other pests is another major
factor in rootstock selection.
Compare and contrast horizontal and vertical resistance
Vertical resistance impacts major functions of specific pathogens. As a result, vertical
resistance is often very effective and very specific to a pathogen race or group, but
sometimes rapidly selected against by the pathogen. In some cases, vertical resistance
may inhibit the initial establishment of pathogens, thereby inhibiting the development of epidemics.
horizontal (polygenic) involves numerous minor processes and defenses
working together that affect most strains of a pathogen. Horizontal resistance may be
slightly less effective against some pathogen strains but is usually longer lasting (Figure
5-2). In some cases, multilines, or mixes of different varieties with different resistance genes, are used to
reduce selection in the pest population to overcome host resistance.
Explain how an IPM program can help prolong the useful life of a resistant cultivar.
IPM helps prevent and reduce pest problems before they can mutate to infect resistant cultivars.
Pesticides, nat. enemies, cultural control, improving varieties.
Describe the classical breeding techniques used to develop resistant plants.
Finding a resistant cultivar and propagating through sexual reproduction.
Explain how tissue culture and genetic engineering techniques are used in the development of
resistant cultivars.
Cell and tissue culture, as well as techniques such as genetic engineering and irradiation, allow plant
breeders to more rapidly develop new varieties of plants without having to carry out the time-consuming
tasks of crossing plants through sexual reproduction and selecting for desirable qualities over many
generations. Genetic engineering allows breeders to transfer genetic material from one organism to
another and opens up vast new resources of pest-resistant genetic material.
List situations where use of non-host plants may be a feasible management solution.
In some situations, when heavy pest infestations occur, resistance breaks down, or control options are
simply too expensive, the best option is to avoid the pest altogether
through the use of alternate nonhost plants. Nonhost plants can be used in crop
rotations to reduce pest numbers. In landscapes, non host plants providing similar aesthetic qualities are
frequently available.
Describe the major biological control approaches used in pest management:
Importation/Classical-Importation, or classical, biological control involves the
deliberate introduction and establishment of natural enemies into areas where they did not previously
exist
conservation and enhancement-Conservation and enhancement of estab
lished natural enemies include any activities that improve survival, dispersal, and reproduction of resident
natural enemies. Many approaches can be taken. Elimination or reduction of pesticides toxic to natural
enemies is an important way of improving biological control
Augmentation- Augmentation involves supplementing the numbers of naturally
occurring biological control agents with releases of laboratory-reared or field-collected
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natural enemies (Figure 5-12). Because it is so much more expensive, augmentative
approaches are usually attempted only when importation and conservation techniques are not promising.
Predator
A predator is an animal that attacks, feeds on, and kills more than one prey during its lifetime. Predators
are usually larger and stronger than their prey. EX: the predatory
arthropods, such as the lady beetle (Figure 5-4) and carabid beetles, lacewings, syrphid flies, ants,
predatory hemipterans, spiders, and predatory mites. In some insect species, both the adult and
immature (larval or nymphal) stages are predaceous
Parasite
A parasite feeds in or on a larger host organism. Parasitic organisms
have a prolonged and specialized relationship with their host, usually parasitizing only one individual or a
few hosts in their lifetime. True parasites often weaken the host but do not kill it outright; in some cases,
they may have little negative impact. Only those that significantly weaken or kill their host are important in
biological control.
Parasitoid
Insects that parasitize and kill other insects are often called parasitoids. Parasitoids are
parasitic during their immature stages and kill their host as they reach maturity. Most
parasitoids are wasps or flies with adults that feed on insect honeydew and plant nectar
and pollen. In certain species, the adult female parasitoid also feeds on hosts.
Because they kill their hosts, insect parasitoids are not considered true parasites.
Antibiosis
Some organisms release toxins or otherwise change conditions so that
the activity or growth of the pest is reduced. Many bacteria and molds secrete antimicrobial substances
that inhibit the growth of other microorganisms.
Antagonists
Organisms that kill or inhibit growth of plant pathogens and other microorganisms are
called antagonists. They may act as predators, parasites, pathogens, and competitors,
or they may have repellent or antibiotic effects.
Allelopathy
occurs when a plant releases chemicals (allelochemicals) that impair growth of other plants nearby. An
example of a plant with allelopathic qualities is the black walnut tree, which produces a toxin that inhibits
growth of most plant species around the base of the tree. Other crop plants with well-demonstrated
allelopathic effects on weeds include barley, rye, and sudangrass. Some weed species also have the
potential to express allelopathic effects, including some Cirsium, Cynodon, and Cyperus spp. Some
organic mulches have also been used for their allelopathic effects.
Competition
Weeds decrease crop yields and negatively influence neighboring plants in landscapes by competing for
light, water, and nutrients. Tilting any of these resources in favor of the host plant can help it outcompete
weeds
Describe some approaches to encourage naturally occurring biological control agents.
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Compare/contrast the role of inundative releases versus inoculative releases in a biological
control program.
In inoculative programs, released natural enemies reproduce in the field and build
up their population so that their progeny provide control for several generations.
Inoculative releases may be used to build up populations of natural enemies earlier in the season than
usual or to establish a natural enemy in an area where it was not previously present. Inoculative releases
are appropriate when the population of an otherwise effective natural enemy is severely devastated by
pesticide applications, unfavorable weather conditions, cultivation practices, or a lack of seasonal hosts.
Inundative releases are aimed at achieving immediate biological control through the activities of the
released individuals. Offspring of released individuals are not expected
to survive to assist in control. Additional releases may be required throughout the season should pest
populations approach damaging levels. Inundative releases are most effective against pests that cause
economic damage only during a limited period of the year and against pests in a controlled environment.
A wide variety of predators and insect parasites have been used in inundative programs and are the
primary method of using microorganisms and nematodes for biological control.
The following practices can be used to conserve or enhance the activities of insect natural
enemies:
selection of pesticide
Another criterion to consider in pesticide use is selectivity—the range of organisms and life stages of
organisms affected by the pesticide. A broad-spectrum
pesticide kills a wide range of pests and non targets, whereas a selective pesticide controls a smaller
group of closely related organisms. Selective pesticides are generally desirable in IPM programs because
they often have less impact on beneficial organisms and lower risks for humans and wildlife. Selectivity
that prevents damage to a crop plant is a key feature of any herbicide applied while the crop is in the field.
Selective pesticides target chemical processes unique to one pest or pest group. Selectivity also is
influenced by the rate of penetration of the toxicant, the binding of the toxicant to the organism’s tissues,
and the speed with which the organism breaks
down the toxicant. Selectivity can also be achieved through the use of application techniques that cause a
pesticide to come into contact with the
target pest and not with nontarget organisms. For example, spraying only the trunks of elm trees to
control elm leaf beetle larvae as they crawl down from the tree canopy to
pupate in the soil leaves the beneficial species in the foliage unharmed (Figure 5-34).
Another example is the use of shields and wipers to direct herbicide applications away
from susceptible plants.
selective timing or placement of pesticide
Plant Diversity and Ant control
Production practices can also be manipulated to benefit natural enemies. A lack of
plant diversity, for instance, can increase a crop’s susceptibility to pest attack and reduce its
attractiveness to natural enemies. For good survival and high reproduction,
natural enemies often require shelter, alter ative food sources, water, overwintering
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sites, and other conditions. Natural enemies of honeydew-producing homopteran insects may also
require protection from ants. Certain ant species, such as the Argentine ant,Iridomyrmex humilis, feed on
honeydew produced by aphids, soft scales, whiteflies, and mealybugs and disrupt biological control by
attacking their predators and parasites (Figure 5-9). It may be necessary to take measures to control
these ants by pruning branches to deny them access to plant canopies or by applying a sticky material to
tree trunks.
Harvesting
Although not much can be done to diminish the ill effects of weather, the
microclimates of natural enemy populations can be made more favorable through
the manipulation of irrigation, use of cover crops, modification of pruning techniques,
or by changes in harvesting practices. For example, border harvesting, where a strip
of alfalfa is left standing after each harvest, benefits hay production by maintaining
populations of predators and parasites of alfalfa pests in the alfalfa field. In addition,
border harvesting also markedly reduces lygus bug migration into cotton and other
crops. Similar benefits can be obtained by border harvesting or staggering the cutting of alfalfa hay fields
that are nearby or adjacent to each other (Figure 5-10). Figure 5-11 compares the abundance of natural
enemy populations in border-harvested alfalfa and conventional alfalfa
Identify the following common generalist predators of insect and mite pests in immature and adult
stages:
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Describe the typical life cycle of an insect parasitoid
Insect parasitoid orders
Most insects that parasitize other insects belong to the orders Hymenoptera (wasps) and Diptera (flies).
Describe the use of nematodes in the biological control of insects.
Nematodes used in insect pest management are called entomopathogenic
nematodes and are packaged, sold, and applied for release inundatively, similar to insecticides. Most
currently available entomopathogenic nematodes are in the families Steinernematidae and
Heterorhabditidae. Entomopathogenic nematodes serve as
vectors of pathogenic bacteria (Figure 5-15),and it is these bacteria that actually kill the
host. The nematodes can be applied to the foliage, soil, or in insect galleries and are
most effective against insects that feed in enclosed areas where moisture levels can
remain high. Applications of nematodes for soil-inhabiting insects should be watered
in to increase efficacy. Table 5-5 lists some commercially available nematodes and the
pests they control. The most important factors are adequate soil moisture and avoid
ance of temperature extremes. Page 107 IPM book
List three types of organisms that are common insect pathogens.
Heterorhabditis bacteriophora, Steinernema carpocapsae, and Steinernema feltiae
List the major group of natural enemies used for the biological control of weeds in California.
Insects in such diverse groups as moths, thrips, mealybugs, scale insects,
wasps, chrysomelid and other beetles, leafminers, gall midges, and others have been successfully used
in biological control programs for weeds.
Identify a weed pest successfully controlled through the use of natural enemies
Worldwide, biological control organisms have been responsible for the control of a
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number of introduced weed species. In California, major successes include the importation of a cochineal
insect, Dactylopius opuntiae, to control two species of prickly pear cactus and the control of the European
native klamathweed with the imported European leaf-feeding beetle Chrysolina quadrigemina (Figure 517)
Dactylopius opuntiae – control prickly pear.
Chrysolina quadrigemina – control klamathween.
Explain why biological control of weeds has been more successful against rangeland and aquatic
weeds than weeds of agricultural crops
These ecosystems usually have a low level of disturbance that enhances natural enemy survival. Also,
unlike a cultivated crop, these systems can be compatible with the slow rate of control often produced by
biological control and the need to maintain
low populations of target weeds to retain natural enemies. Most weeds targeted for
biological control are specific problem weeds that are toxic to livestock or have some other undesirable
quality. Once target weeds are removed, the area must be man
aged so that desirable wild plants will take their place. In crop production systems, weed management is
directed at complexes of weed species that compete with crop plants. If one species is removed by
biological control, another troublesome species is likely to take its place. As a result, classical biological
control has less potential for weed management in agricultural or landscape systems.
Describe the role of crop competitiveness as a biological approach to weed control
Weeds decrease crop yields and negatively influence neighboring plants in landscapes by competing for
light, water, and nutrients. Tilting any of these resources in favor of the host plant can help it outcompete
weeds. For instance, using transplants can give the host plant an advantage by shading certain weed
species and giving the host a head start. Managing water and nutrients can also effectively exploit crop
competitiveness. Banding and side-dressing of fertilizer applications, for instance, is more favorable for
crop growth than for weed growth.
Disease suppressive soil
Are soils in which disease incidence remains low even though a pathogen, a susceptible host, and env.
conditions that favor disease development are present. Suppression may invoke a small number of
microbial organisms antagonistic to specific pathogens.
Cultural Control
Describe the advantages of using cultural controls in an integrated pest management program
Cultural practices can sometimes be used to modify the environment, making it less favorable to pest
invasion, reproduction, survival, or dispersal. For instance, in some cases simple changes in the timing of
irrigation may reduce disease incidence or weed germination; or, a change in planting or harvest time can
allow a crop to escape pest invasion. Cultural controls are generally
familiar, simple, and inexpensive, and they can often be incorporated into management
systems with only minor modifications. Some of the oldest pest control practices used by growers,
foresters, and other resource managers include cultural methods. In fact, some practices have been so
routinely used and are so closely associated with management practices that they are not clearly
recognized as pest control strategies. Cultural pest control is most often used as a preventive pest
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management tool. To properly implement cultural control measures, it is essential to have a good
understanding of crop and pest biology, ecology, and phenology. Special attention should be paid to the
weak links in the life cycle of the pest.
Describe how site selection can affect pest problems.
pest problems can be prevented by selecting a site that is pest-free, or by choosing a crop, plant species,
or variety that is particularly well suited to the site. Before planting, evaluate whether the site and the
resource being planted are a profitable match
or whether the combination will create or aggravate pest problems. For example, trees or shrubs are
often planted in landscapes without regard to the environmental conditions favorable to that plant (Figure
5-21). Plants poorly adapted to conditions at their site are more prone to insect and disease damage and
generally do not perform well. Like wise, it is good management to avoid fields with weeds that are
potentially troublesome and hard to control in a crop. Instead, plant an alternative crop where available
herbicides, cultural practices, or crop competitiveness will help reduce troublesome weeds. Sampling for
nematodes, propagules of potentially damaging pathogens, and weed seeds, and looking at the field
history prior to planting can help determine whether the site is suitable for a given type of crop.
List 6 sanitation techniques CULTURAL
-Use certified seed, tubers, or rootstock to prevent the spread of nematodes, weed seeds, and viral,
bacterial, and fungal pathogens that may be carried in contaminated plant material.
-Thoroughly clean with steam or pressurized water all equipment as it moves between different sites to
prevent the spread of pathogens, nematodes, and weeds.
-Use clean irrigation water. Do not irrigate with tailwater from fields infested with root knot nematodes or
other soilborne pathogens or pests; do not use water that may carry runoff containing harmful herbicides.
-Install screens in pipes bringing irrigation water from canals or ditches to filter out seeds, rhizomes, and
other weed parts.
-Remove or clean up unharvested crops or areas That might
provide overwintering habitat for pests.
-Eliminate weedy borders
Describe the benefits of destroying alternate hosts in a pest management program.
Destroying alternate hosts can effectively suppress certain pest populations. For example, some weeds
or other plants act as alternate hosts for insect and pathogen pests; destruction of these reservoirs can
aid in suppressing pest populations. The control of curly top virus in sugar beets involves the destruction
of weeds that are alternate hosts of the beet leafhopper, Circulifer tenellus. Lettuce root aphid,
Pemphigus bursarius, overwinters in galls on poplar trees. Lettuce growers have successfully reduced
populations of this aphid below damaging levels in their fields by eliminating poplar windbreaks.
Habitat Modification
Pest problems occur when conditions essential for survival, that is, food, shelter, alternate hosts, and
proper environmental conditions, are favorable. Habitat modification intentionally changes the
environment to limit availability of one or more of these requirements, thus reducing the suitability of the
host to pest populations. Habitat modification is very important in vertebrate control. For example, weeds,
ground cover, and litter provide food and cover for meadow mice. Eliminating these areas in
and around crops, turf and landscape, and cultivated areas reduces the potential of these areas to
support these and other vertebrate pests. Habitat modification is effective in limiting numerous insect
pests as well. For example, draining areas containing standing water reduces breeding sites for
mosquitoes and is an important management technique. Habitat modification is also a critical element in
the management of pest flies in poultry houses and dairies. Flies have three basic developmental
29
requirements: food, warmth, and moisture. Eliminating any of these in the poultry house, barn, or
barnyard can break the life cycle of the fly and reduce the problem. Although eggs may hatch, larvae
cannot develop into flies without food, warmth, and moisture
Intercropping
Intercropping involves growing more than one crop in a field at the same time: multiple crops are planted
in alternating strips or intersown into a main crop. Intercropping is sometimes used to reduce pests. For
instance, older stands of alfalfa can be overseeded with oats to reduce weed pressure, and the harvested
alfalfa-oat mix is sold as a forage crop. In cotton, a trap crop of alfalfa can be planted in strips to keep
damaging lygus bugs out of the crop (Figure 5-24), since lygus does little damage
to alfalfa hay grown for forage. In new orchard plantings, intercropping is sometimes used to produce
income prior to the maturing of the trees.
Describe how smother crops and cover crops can be used in an IPM program.
Smother crops are grown for their ability to suppress weeds and for their cash value.
They are effectively employed in crop rotations following the main crop and are planted at high densities
to rapidly occupy a site. Cereals, sorghum, safflower, field corn, and
domestic sunflowers have been effectively used as smother crops.
Cover crops are noncrop plant species grown either concurrently with the host
crop (usually perennial plants) or in rotation with annual crops; they are generally not
harvested. Cover crops can suppress weeds; provide nutrients to the soil; and provide
food and shelter to beneficial insects, mites, and spiders (Figure 5-23). They are also
valued for their ability to improve soil texture, increase organic matter, increase water
infiltration rates, reduce pesticide runoff into surface water, and reduce soil erosion.
Successful cover crop varieties often planted in orchards and vineyards in California
include strawberry clover, annual clover, Native ground covers are used as cover crops in many
vineyards to minimize weed growth, improve soil water penetration, and reduce erosion. cereal grasses,
annual grasses, and vetches, or a combination of species selected for their ability to improve soil fertility
or attract beneficial insects.
An example of a cover crop improving biological control is the use of a vetch cover
crop in vineyards to improve biological control of mealybugs. Vetch supplies ants with
adequate amounts of nectar and keeps them from moving into vines, thereby reducing
ants’ interference with the natural enemies of grape pests—-especially parasitic wasps
that can control the mealybugs. However, in some vineyards cover crops can increase
early populations of the caterpillar pest omnivorous leafroller by providing it with an alternate food source.
Advantages vs disadvantages of cover crops
Advantage
Disadvantage
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-decreases soil erosion,
-increases organic matter
-improves soil structure and water infiltration
-decreases water and pesticide runoff
-may add or conserve nitrogen
-may suppress weed growth
-may attract or provide nectar source for beneficial
insects, spiders, and mites
-depletes soil moisture
-may decrease availability of plant nutrients, especially
nitrogen
-may require additional irrigation and nitrogen applications
-may increase weeds
-may attract arthropod and rodent pests
-may increase nematode populations
-increases danger offrost damage to trees or vines
-increases associated costs
List the attributes of pests successfully managed with crop rotation practices
Crop rotations have provided effective control for certain host-specific plant pathogens, nematodes, and
insects by disrupting the pests’ life cycle and by changing environmental conditions to deter certain
species. These pests tend to be soil borne and immobile. The host range of the pest cannot be so
extensive that a suitable alternate crop cannot be found. Pests that attack only one or a few closely
related crops are the best candidates. And, the pest population should not be able to survive after a 1- or
2-year absence of the living host. Good candidates for management by crop rotation include soil- and
root-dwelling nematodes and soilborne pathogens that do not produce airborne spores and have limited
host ranges. When rotation is used for disease and nematode management, alternate weed hosts must
be controlled as well.
Describe how adjusting the planting date can benefit weed control.
For weed management, choose a planting time that favors germination of the
crop over key weed species. For instance, in many parts of California, fall alfalfa planting can be adjusted
to avoid both late-germinating summer weeds and late-fall-germinating winter weeds. However, crops
planted too late in fall will germinate and grow slowly, allowing winter weeds to become well established.
If fields are infested with field bindweed, perennial grasses, or nutsedge, planting in early fall will ensure
that alfalfa is established and vigorously growing when these perennials start growing in spring.
Adjustments in the timing of planting can also aid in insect and disease management. Winter-grown
carrots and potatoes in California can be planted when the potato cyst nematode is not active, avoiding
exposure in early crop development stages when the pest is most damaging. In sugar beets, beet yellow
virus and beet mosaic virus have been kept under control by following strict planting programs that
allowed no early-spring plantings in or adjacent to growing districts where sugar beets were overwintered
in them field. Certain seedling pathogens, such as Thielaviopsis basicola and Pythium ultimum, can be
avoided in cotton by planting later to reduce the chance of infection. Timing spring row crop planting to
allow sufficient time for winter row crop residues to decompose is an important cultural practice used in
coastal row crop production to prevent seedcorn maggot damage to seeds and seedlings. Using a chain
drag behind the seed shanks on the planter also helps to camouflage the seed row from adult egg laying
flies.
Describe how early harvest can reduce pest problems.
Harvest can also be timed to limit or avoid pest damage. Early harvest can reduce the
number of generations of nematodes that can damage a root crop. In northern California potato fields,
early harvest effectively reduces the incidence of nematode blemishes on tubers by shortening the time
nematodes have available to reproduce. Early harvest is also beneficial in the management of various
31
insect pests. Early harvest of coastal avocados can help control greenhouse thrips on tough skinned
varieties by minimizing crop-to-crop overlap and removing much of the insect population before it has
time to move to a new crop. In some situations, early harvest of alfalfa hay can eliminate need for treating
alfalfa weevil or alfalfa caterpillar.
Describe how poor irrigation practices can lead to pathogen and weed pest problems.
Excess soil water excludes oxygen that plant roots need to survive and is a primary factor in the
development of many root and crown diseases, such as Phytophthora root rot. The fungi causing these
diseases are present in many soils but become damaging when excessive moisture favors them. Excess
water and poor drainage in low areas of fields or landscapes also favor numerous hard-to-control weeds
such as nutsedge and barnyardgrass. Underwatering, or drought stress, on the other hand, may cause
wilting, sunburn, sunscald, and branch cracking that can allow invasion of pathogens and attract boring
insects, or it can stress plants to the extent that they cannot overcome attack by pests. This is especially
true of conifers in the landscape. Crop competitiveness is reduced and weed invasion may occur.
List three pest problems associated with excess nitrogen applications.
While this may be true, overfertilization may attract or enhance development of many pest species.
Excess nitrogen on nectarines, for example, results in increased levels of brown rot (Moniliniafructicola),
oriental fruit moth (Grapholita molesta), and peach twig borer (Anarsia lineatella). Excessive nitrogen
levels are also a contributing factor in the incidence of brown patch, Rhizoc…