Plant Pests and Their Control

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Chapter 6

• Plant Pests and Their Control

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• Anything that impairs the healthy growth and
  maturation of a plant may be regarded as an
  injurious agent.
• Some injurious agents cannot be transmitted.
• Agents that can be transmitted from one plant to
  another are regarded as either infectious or
  infestious.
• An infected plant has the injurious agent active
  within it.
• An infested plant has the agent active on its
  surface.

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• A parasite is an organism incapable of
  manufacturing its own food.
• The parasitic insects, fungi, bacteria, viruses,
  and nematodes, as well as the weeds, are usually
  referred to as plant pests.

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• Entomology is the study of insects, their effects
  on plants, and their control.
• Plant pathology is the study of plant diseases,
  their causes, and their control.
• Bacteriology is the study of bacteria.
• Mycology is the study of fungi.
• Virology is the study of viruses.
• Nematology is the study of nematodes.
• Weed science is the study of weeds and their
  control.

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• Insects constitute over 2/3 of all the animal
  species on the planet and are surpasses only by
  microbes in sheer numbers of individuals.
• In the animal kingdom, the major divisions are
  known as phyla.
• The phylum Anthropoda contains the class Insecta,
  or the insects.

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• The exoskeleton is the hard protective covering
  of the insects body, and has helped ensure
  survival of insects through centuries of
  evolution and environmental stress.
• The exoskeleton is composed principally of
  chitin, a nitrogenous
• polysaccharide compound
• that resists water, alcohol,
• acids, and alkalis.

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• The mouthparts of insects determine how they feed
  on plants and the symptoms of injury that are
  manifested.
• Six common types of mouthparts
• Chewing
• Siphoning
• Sponging
• Rasping-sucking
• Piercing-sucking
• Chewing-lapping

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• The digestive system is a tube that extends from
  the mouth of the insect to the anus.
• The respiratory system combines expansion and
  contraction of the abdomen with diffusion to
  exchange oxygen and carbon dioxide in the cells
  and tissues of the insect.
• The nervous system is made up of groups of
  specialized cells called ganglia and nerve fibers
  that join the ganglia to other parts of the
  insects body.

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• No members of the animal kingdom transform more
  dramatically during their development than
  insects.
• The changes in insect form as they grow are
  termed metamorphosis.
• Complete metamorphosis includes four stages of
  development
• Egg
• Larva
• Pupa
• Adult

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• The effect of disease in plants is injury,
  manifested in symptoms of abnormal growth.
• The United States loses and estimated 15-20 of
  the crop productivity each year due to plant
  diseases.
• The most important causes of disease in plants
  are the bacteria, fungi, viruses, and nematodes.

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5 important characteristics of

• Bacteria
• Members if the plant kindom.
• Nonchlorophyllous
• Single-celled
• Three body forms (spherical or coccus, rod-shaped
  or bacillus, spiral-shaped or spirillus)
• Reproduction by simple cell division.

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• Fungi
• Members of the plant kingdom
• Nonchlorophyllous
• Their vegetative body ranges in size from a
  single cell to a thread-like multi-cellular
  structure termed a mycelium.
• Reproduction by formation of spores.
• Classification is on the basis of life cycle,
  specifically how the vegetative and reproductive
  organs develop.

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• Viruses
• Their categorization as plants or animals is
  undetermined.
• Nonchlorophyllous
• Composed of nucleic acids and proteins
• Smallest of the pathogens, visible only with an
  electron microscope.
• Plant viruses appear most commonly in two
  morphological forms a long, narrow, tube-like
  rod and an isometrical polyhedron (shape with
  many sides of equal length)

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• Nematodes
• Members of the animal kingdom
• Feed on both plants and animals.
• Plant nematodes average about 1 millimeter in
  length.
• Body wall usually transparent, with an outer
  covering termed cuticle.
• Feeding apparatus consists of mouthparts equipped
  with buccal spear used to puncture the host cell
  to with draw cellular fluids.

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• Slugs and Snails
• Members of the animal kingdom.
• Macroscopic in size.
• Nocturnal feeders on plant leaves and stems.
• Slugs lack the shell that is common to snails.
• Leave a slimy trail on the soil surface as they
  move.

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• Parasitic seed plants
• Weakly chlorophyllous but usually incapable of
  meeting their own nutritional needs.
• Connect to the vascular tissue of chlorophyllous
  higher plants.
• Varying levels of parasitism
• Epiphytic
• Hemiparasitic
• Fully parasitic

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• For a plant disease to occur there must be a
  casual agent, the pathogen in the vicinity of a
  susceptible plant, the host.
• The infectious form of the pathogen is termed the
  inoculum.
• As long as the inoculum is only on the host, the
  plant is termed infested.
• Once the pathogen is penetrated the hosts
  tissues, the plant is termed infected.

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• Responses to pathogenic irritants and insects are
  termed symptoms.
• Symptoms may be influenced by an assortment of
  factors including
• Species of host
• Environment
• Quantity of inoculum or insects
• When fungi invade the tender stem tissue of a
  young seedling, damping-off develops.

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• Lack of light turns a plant yellow in a condition
  termed etiolation.
• When the plant turns yellow but does not lack
  light the symptom is termed chlorosis.

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• Rotting results from a destruction of the host
  cells that causes a release of the cellular
  fluids.
• When tissue become desiccated or dried out and
  dies, it usually turns brown or black, and is
  said to be necrotic.
• When all or part of the plant is reduced in size
  as a result of pathogens (especially viruses),
  insects, and nematodes it is termed dwarfing.
• A reduction in cell size is termed hypotrophy.
• A reduction in cell number is termed
• hypoplasia.

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• A weed may be defined as a plant having no
  positive economic value and/or growing in a place
  where it is not desired.
• Weeds compete with other plants for the materials
  both need to grow and thrive.
• Within a local area, weeds are distributed as
  sees, stolons, roots, bulbs, rhizomes, or tubers.

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• Some natural agents of dissemination of weeds
• Flowing water
• Wind
• Birds
• Livestock and other animals
• Some artificial agents of dissemination of weeds
• Cultivating tools
• Vehicles
• Clothing
• Transplanting desired plants from one area to
  another and moving weeds with them.

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• Other causes of injury other than insects, weeds,
  and disease
• Rodents
• Lawnmowers
• People
• Vandalism
• Quantitative damage- all or part of the host
  plant is destroyed by the antagonistic agent.
• Qualitative damage- host suffers a loss of
  appearance and sale value.

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Three Levels of Pest Control

• Partial control- most common type homeowner may
  spray a broad spectrum (all-purpose) pesticide
  and the plant may still show symptoms, but not as
  severely as if the had not been sprayed.
• Absolute control- is total control all symptoms
  of pest injury are absent.
• Profitable control- the level attained when
  monetary returns on the crop exceed the cost of
  the control measures.

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• Partial control is the most common type of pest
  control, but profitable control is the most
  sought by growers.
• The determine the potential profitability of a
  control measure, three factors must be
  considered
• Value of single crop plant
• Ultimate value of the crop
• Average loss over a period of
• years

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• Exclusion- first principle of control includes
  all the measures designed to keep a pest from
  becoming established in an area.
• Eradication- the principle that seeks to remove
  or eliminate pests that are already in, on, or
  near plants in infested areas.
• Protection- principle of control that sets up a
  barrier between the host plants and the pests to
  which they are susceptible.
• Resistance- fourth principle of control attempt
  to change the plants morphology and/or genotype
  so that it will suffer less from diseases and
  insects.

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When using pesticides, the choice of formulation
is based on

• The size of the crop area being treated.
• The amount of active ingredient being applied.
• The other materials being applied along with the
  pesticide, such as other pesticides and
  fertilizers.
• Cost
• Safety
• Ease of application

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• The safe use of chemical pesticides requires a
  respect for their toxicity.
• All manufacturers and distributors of pesticides
  are required by federal law to provide explicit
  information about their products ingredients,
  formulations, toxicity, and proper rates of
  application, and about the specific pests
  controlled and proper means of safe handling.
• Adjuvants- chemical additives that improve the
  performance of the pesticide with which they are
  combined.

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

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• Plant extracts- chemicals found naturally in
  certain plants when extracted, concentrated, and
  applied to vulnerable pests, these natural
  chemicals can interfere with the growth and
  development of certain pests.
• Microorganisms- can be used as antagonists
  against other organisms include various species
  of bacteria, fungi, protozoa, viruses, and
  nematodes. They are applied to host crops where
  they infect and destroy the target pest.
• Microbe-derived pesticides- use the natural
  antibiotics and other compounds extracted from
  microorganisms to control plant pests.

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• Pyrethroids- synthetic version of the natural
  extract, pyrethrins. They tend to control a wider
  range of pests and remain effective longer than
  the natural pyrethins.
• Soaps- light oils made from plants works against
  soft bodied insects by penetrating their outer
  layer and dehydrating their interiors.
• Insect growth regulators- disrupt the growth and
  development of insects. The effect is usually
  hormonal and interferes with the metamorphosis of
  the insects.

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• Chronicotinyls- similar to insect growth
  regulators that act by impeding the normal
  functioning of the insect nervous system. They
  are systemic and can be applied as either
  granulars or as sprays.
• Pheromones- chemical cues used by insects to
  communicate when synthesized, sex pheromones can
  be used as baits to attract and trap certain
  insects. It is more useful as a management and
  monitoring tool than a control measure.

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Eight symptoms of injury following infestation by
insects

• Wilting
• Color changes
• Rotting
• Death of tissue
• Dwarfing
• Increase in size
• Tunneling
• Holes