Chapter 6Chapter 6

Plant Pests and Their ControlPlant Pests and Their Control

Anything that impairs the healthy Anything that impairs the healthy growth and maturation of a plant growth and maturation of a plant may be regarded as an injurious may be regarded as an injurious agent.agent.

Some injurious agents cannot be Some injurious agents cannot be transmitted.transmitted.

Agents that can be transmitted from Agents that can be transmitted from one plant to another are regarded as one plant to another are regarded as either infectious or infestious.either infectious or infestious.

An infected plant has the injurious An infected plant has the injurious agent active within it.agent active within it.

An infested plant has the agent An infested plant has the agent active on its surface.active on its surface.

A parasite is an organism incapable of A parasite is an organism incapable of manufacturing its own food.manufacturing its own food.

The parasitic insects, fungi, bacteria, The parasitic insects, fungi, bacteria, viruses, and nematodes, as well as the viruses, and nematodes, as well as the weeds, are usually referred to as plant weeds, are usually referred to as plant pests.pests.

Entomology is the study of insects, their Entomology is the study of insects, their effects on plants, and their control.effects on plants, and their control.

Plant pathology is the study of plant Plant pathology is the study of plant diseases, their causes, and their control.diseases, their causes, and their control.

Bacteriology is the study of bacteria.Bacteriology is the study of bacteria. Mycology is the study of fungi.Mycology is the study of fungi. Virology is the study of viruses.Virology is the study of viruses. Nematology is the study of nematodes.Nematology is the study of nematodes. Weed science is the study of weeds and Weed science is the study of weeds and

their control.their control.

Insects constitute over 2/3 of all the Insects constitute over 2/3 of all the animal species on the planet and are animal species on the planet and are surpasses only by microbes in sheer surpasses only by microbes in sheer numbers of individuals.numbers of individuals.

In the animal kingdom, the major In the animal kingdom, the major divisions are known as phyla.divisions are known as phyla.

The phylum Anthropoda contains the The phylum Anthropoda contains the class Insecta, or the insects.class Insecta, or the insects.

The exoskeleton is the hard The exoskeleton is the hard protective covering of the insect’s protective covering of the insect’s body, and has helped ensure survival body, and has helped ensure survival of insects through centuries of of insects through centuries of evolution and environmental stress.evolution and environmental stress.

The exoskeleton is composed The exoskeleton is composed principally of chitin, a nitrogenous principally of chitin, a nitrogenous

polysaccharide compound polysaccharide compound

that resists water, alcohol, that resists water, alcohol,

acids, and alkalis.acids, and alkalis.

The mouthparts of insects determine how they The mouthparts of insects determine how they feed on plants and the symptoms of injury feed on plants and the symptoms of injury that are manifested.that are manifested.

Six common types of mouthparts:Six common types of mouthparts:

– ChewingChewing– SiphoningSiphoning– SpongingSponging– Rasping-suckingRasping-sucking– Piercing-suckingPiercing-sucking– Chewing-lappingChewing-lapping

The digestive system is a tube that The digestive system is a tube that extends from the mouth of the insect extends from the mouth of the insect to the anus.to the anus.

The respiratory system combines The respiratory system combines expansion and contraction of the expansion and contraction of the abdomen with diffusion to exchange abdomen with diffusion to exchange oxygen and carbon dioxide in the cells oxygen and carbon dioxide in the cells and tissues of the insect.and tissues of the insect.

The nervous system is made up of The nervous system is made up of groups of specialized cells called groups of specialized cells called ganglia and nerve fibers that join the ganglia and nerve fibers that join the ganglia to other parts of the insects ganglia to other parts of the insects body.body.

No members of the animal kingdom No members of the animal kingdom transform more dramatically during their transform more dramatically during their development than insects.development than insects.

The changes in insect form as they grow The changes in insect form as they grow are termed metamorphosis.are termed metamorphosis.

Complete metamorphosis includes four Complete metamorphosis includes four stages of development:stages of development:– EggEgg– LarvaLarva– PupaPupa– AdultAdult

The effect of disease in plants is injury, The effect of disease in plants is injury, manifested in symptoms of abnormal manifested in symptoms of abnormal growth.growth.

The United States loses and estimated The United States loses and estimated 15-20% of the crop productivity each 15-20% of the crop productivity each year due to plant diseases.year due to plant diseases.

The most important causes of disease The most important causes of disease in plants are the bacteria, fungi, in plants are the bacteria, fungi, viruses, and nematodes.viruses, and nematodes.

5 important characteristics 5 important characteristics of:of:

Bacteria:Bacteria:– Members if the plant kindom.Members if the plant kindom.– NonchlorophyllousNonchlorophyllous– Single-celledSingle-celled– Three body forms (spherical or coccus, Three body forms (spherical or coccus,

rod-shaped or bacillus, spiral-shaped or rod-shaped or bacillus, spiral-shaped or spirillus)spirillus)

– Reproduction by simple cell division.Reproduction by simple cell division.

Fungi:Fungi:– Members of the plant kingdomMembers of the plant kingdom– Non-chlorophyllousNon-chlorophyllous– Their vegetative body ranges in size Their vegetative body ranges in size

from a single cell to a thread-like multi-from a single cell to a thread-like multi-cellular structure termed a mycelium.cellular structure termed a mycelium.

– Reproduction by formation of spores.Reproduction by formation of spores.– Classification is on the basis of life cycle, Classification is on the basis of life cycle,

specifically how the vegetative and specifically how the vegetative and reproductive organs develop.reproductive organs develop.

Viruses:Viruses:– Their categorization as plants or animals Their categorization as plants or animals

is undetermined.is undetermined.– Non-chlorophyllousNon-chlorophyllous– Composed of nucleic acids and proteinsComposed of nucleic acids and proteins– Smallest of the pathogens, visible only Smallest of the pathogens, visible only

with an electron microscope.with an electron microscope.– Plant viruses appear most commonly in Plant viruses appear most commonly in

two morphological forms: a long, two morphological forms: a long, narrow, tube-like rod and an isometric narrow, tube-like rod and an isometric polyhedron (shape with many sides of polyhedron (shape with many sides of equal length)equal length)

Nematodes:Nematodes:– Members of the animal kingdomMembers of the animal kingdom– Feed on both plants and animals.Feed on both plants and animals.– Plant nematodes average about 1 Plant nematodes average about 1

millimeter in length.millimeter in length.– Body wall usually transparent, with an Body wall usually transparent, with an

outer covering termed cuticle.outer covering termed cuticle.– Feeding apparatus consists of mouthparts Feeding apparatus consists of mouthparts

equipped with equipped with buccal spearbuccal spear used to used to puncture the host cell to with draw puncture the host cell to with draw cellular fluids.cellular fluids.

Slugs and Snails:Slugs and Snails:– Members of the animal kingdom.Members of the animal kingdom.– Macroscopic in size.Macroscopic in size.– Nocturnal feeders on plant leaves and Nocturnal feeders on plant leaves and

stems.stems.– Slugs lack the shell that is common to Slugs lack the shell that is common to

snails.snails.– Leave a slimy trail on the soil surface as Leave a slimy trail on the soil surface as

they move.they move.

Parasitic seed plants:Parasitic seed plants:– Weakly chlorophyllous but usually Weakly chlorophyllous but usually

incapable of meeting their own incapable of meeting their own nutritional needs.nutritional needs.

– Connect to the vascular tissue of Connect to the vascular tissue of chlorophyllous higher plants.chlorophyllous higher plants.

– Varying levels of parasitism:Varying levels of parasitism: Epiphytic Epiphytic HemiparasiticHemiparasitic Fully parasiticFully parasitic

For a plant disease to occur there For a plant disease to occur there must be a casual agent, the must be a casual agent, the pathogen in the vicinity of a pathogen in the vicinity of a susceptible plant, the host.susceptible plant, the host.

The infectious form of the pathogen The infectious form of the pathogen is termed the inoculum.is termed the inoculum.

As long as the inoculum is only on the As long as the inoculum is only on the host, the plant is termed infested.host, the plant is termed infested.

Once the pathogen is penetrated the Once the pathogen is penetrated the host’s tissues, the plant is termed host’s tissues, the plant is termed infected.infected.

Responses to pathogenic irritants Responses to pathogenic irritants and insects are termed symptoms.and insects are termed symptoms.

Symptoms may be influenced by an Symptoms may be influenced by an assortment of factors including:assortment of factors including:– Species of hostSpecies of host– EnvironmentEnvironment– Quantity of inoculum or insectsQuantity of inoculum or insects

When fungi invade the tender stem When fungi invade the tender stem tissue of a young seedling, damping-tissue of a young seedling, damping-off develops.off develops.

Lack of light turns a plant yellow in a Lack of light turns a plant yellow in a condition termed etiolation.condition termed etiolation.

When the plant turns yellow but does When the plant turns yellow but does not lack light the symptom is termed not lack light the symptom is termed chlorosis.chlorosis.

Rotting results from a destruction of the host Rotting results from a destruction of the host cells that causes a release of the cellular cells that causes a release of the cellular fluids.fluids.

When tissue become desiccated or dried out When tissue become desiccated or dried out and dies, it usually turns brown or black, and and dies, it usually turns brown or black, and is said to be necrotic.is said to be necrotic.

When all or part of the plant is reduced in When all or part of the plant is reduced in size as a result of pathogens (especially size as a result of pathogens (especially viruses), insects, and nematodes it is termed viruses), insects, and nematodes it is termed dwarfing.dwarfing.

A reduction in cell size is termed hypotrophy.A reduction in cell size is termed hypotrophy. A reduction in cell number is termedA reduction in cell number is termed

hypoplasia.hypoplasia.

A weed may be defined as a plant A weed may be defined as a plant having no positive economic value having no positive economic value and/or growing in a place where it is and/or growing in a place where it is not desired.not desired.

Weeds compete with other plants for Weeds compete with other plants for the materials both need to grow and the materials both need to grow and thrive.thrive.

Within a local area, weeds are Within a local area, weeds are distributed as sees, stolons, roots, distributed as sees, stolons, roots, bulbs, rhizomes, or tubers.bulbs, rhizomes, or tubers.

Some natural agents of dissemination Some natural agents of dissemination of weeds:of weeds:– Flowing waterFlowing water– WindWind– Birds Birds – Livestock and other animalsLivestock and other animals

Some artificial agents of Some artificial agents of dissemination of weeds:dissemination of weeds:– Cultivating tools Cultivating tools – VehiclesVehicles– ClothingClothing– Transplanting desired plants from one Transplanting desired plants from one

area to another and moving weeds with area to another and moving weeds with them.them.

Other causes of injury other than Other causes of injury other than insects, weeds, and disease:insects, weeds, and disease:– RodentsRodents– LawnmowersLawnmowers– PeoplePeople– VandalismVandalism

Quantitative damage-Quantitative damage- all or part of all or part of the host plant is destroyed by the the host plant is destroyed by the antagonistic agent.antagonistic agent.

Qualitative damage-Qualitative damage- host suffers a host suffers a loss of appearance and sale value.loss of appearance and sale value.

Three Levels of Pest Control:Three Levels of Pest Control:

Partial controlPartial control- most common type; - most common type; homeowner may spray a broad spectrum homeowner may spray a broad spectrum (all-purpose) pesticide and the plant may (all-purpose) pesticide and the plant may still show symptoms, but not as severely still show symptoms, but not as severely as if the had not been sprayed.as if the had not been sprayed.

Absolute controlAbsolute control- is total control; all - is total control; all symptoms of pest injury are absent.symptoms of pest injury are absent.

Profitable controlProfitable control- the level attained when - the level attained when monetary returns on the crop exceed the monetary returns on the crop exceed the cost of the control measures.cost of the control measures.

Partial control is the most common Partial control is the most common type of pest control, but profitable type of pest control, but profitable control is the most sought by control is the most sought by growers.growers.

The determine the potential The determine the potential profitability of a control measure, profitability of a control measure, three factors must be considered:three factors must be considered:– Value of single crop plantValue of single crop plant– Ultimate value of the cropUltimate value of the crop– Average loss over a period ofAverage loss over a period of

yearsyears

ExclusionExclusion- first principle of control; includes all - first principle of control; includes all the measures designed to keep a pest from the measures designed to keep a pest from becoming established in an area.becoming established in an area.

EradicationEradication- the principle that seeks to remove or - the principle that seeks to remove or eliminate pests that are already in, on, or near eliminate pests that are already in, on, or near plants in infested areas.plants in infested areas.

ProtectionProtection- principle of control that sets up a - principle of control that sets up a barrier between the host plants and the pests to barrier between the host plants and the pests to which they are susceptible.which they are susceptible.

ResistanceResistance- fourth principle of control; attempt to - fourth principle of control; attempt to change the plant’s morphology and/or genotype change the plant’s morphology and/or genotype so that it will suffer less from diseases and so that it will suffer less from diseases and insects.insects.

When using pesticides, the When using pesticides, the choice of formulation is based choice of formulation is based

on:on:

The size of the crop area being treated.The size of the crop area being treated. The amount of active ingredient being The amount of active ingredient being

applied.applied. The other materials being applied along The other materials being applied along

with the pesticide, such as other with the pesticide, such as other pesticides and fertilizers.pesticides and fertilizers.

CostCost SafetySafety Ease of applicationEase of application

The safe use of chemical pesticides The safe use of chemical pesticides requires a respect for their toxicity.requires a respect for their toxicity.

All manufacturers and distributors of All manufacturers and distributors of pesticides are required by federal law to pesticides are required by federal law to provide explicit information about their provide explicit information about their products ingredients, formulations, products ingredients, formulations, toxicity, and proper rates of application, toxicity, and proper rates of application, and about the specific pests controlled and about the specific pests controlled and proper means of safe handling.and proper means of safe handling.

AdjuvantsAdjuvants- chemical additives that - chemical additives that improve the performance of the improve the performance of the pesticide with which they are combined.pesticide with which they are combined.

Integrated pest management (IPM) is a Integrated pest management (IPM) is a multifaceted approach to pest control multifaceted approach to pest control where one may only use chemical where one may only use chemical pesticides only when needed and applies pesticides only when needed and applies the principles of control by carefully the principles of control by carefully balancing the relationship existing among balancing the relationship existing among the crop hosts, the production the crop hosts, the production environment, and the plant pests to which environment, and the plant pests to which the crops are susceptible.the crops are susceptible.

Plant extractsPlant extracts- chemicals found naturally in - chemicals found naturally in certain plants; when extracted, certain plants; when extracted, concentrated, and applied to vulnerable concentrated, and applied to vulnerable pests, these natural chemicals can interfere pests, these natural chemicals can interfere with the growth and development of certain with the growth and development of certain pests.pests.

MicroorganismsMicroorganisms- can be used as antagonists - can be used as antagonists against other organisms include various against other organisms include various species of bacteria, fungi, protozoa, viruses, species of bacteria, fungi, protozoa, viruses, and nematodes. They are applied to host and nematodes. They are applied to host crops where they infect and destroy the crops where they infect and destroy the target pest.target pest.

Microbe-derived pesticidesMicrobe-derived pesticides- use the natural - use the natural antibiotics and other compounds extracted antibiotics and other compounds extracted from microorganisms to control plant pests.from microorganisms to control plant pests.

PyrethroidsPyrethroids- synthetic version of the - synthetic version of the natural extract, pyrethrins. They tend to natural extract, pyrethrins. They tend to control a wider range of pests and control a wider range of pests and remain effective longer than the natural remain effective longer than the natural pyrethins.pyrethins.

SoapsSoaps- light oils made from plants; - light oils made from plants; works against soft bodied insects by works against soft bodied insects by penetrating their outer layer and penetrating their outer layer and dehydrating their interiors. dehydrating their interiors.

Insect growth regulatorsInsect growth regulators- disrupt the - disrupt the growth and development of insects. growth and development of insects. The effect is usually hormonal and The effect is usually hormonal and interferes with the metamorphosis of interferes with the metamorphosis of the insects.the insects.

ChronicotinylsChronicotinyls- similar to insect growth - similar to insect growth regulators that act by impeding the regulators that act by impeding the normal functioning of the insect nervous normal functioning of the insect nervous system. They are systemic and can be system. They are systemic and can be applied as either granulars or as sprays. applied as either granulars or as sprays.

PheromonesPheromones- chemical cues used by - chemical cues used by insects to communicate; when insects to communicate; when synthesized, sex pheromones can be synthesized, sex pheromones can be used as baits to attract and trap certain used as baits to attract and trap certain insects. It is more useful as a insects. It is more useful as a management and monitoring tool than management and monitoring tool than a control measure.a control measure.

Eight symptoms of injury following Eight symptoms of injury following infestation by insects:infestation by insects:

WiltingWilting Color changes Color changes RottingRotting Death of tissueDeath of tissue DwarfingDwarfing Increase in sizeIncrease in size TunnelingTunneling Holes Holes