Chapter 6 Plant Pests and Their Control n

Chapter 6 Plant Pests and Their Control

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

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

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

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

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

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

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

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

n The effect of disease in plants is injury, manifested in symptoms of abnormal growth. n The United States loses and estimated 1520% of the crop productivity each year due to plant diseases. n The most important causes of disease in plants are the bacteria, fungi, viruses, and nematodes.

5 important characteristics of: n Bacteria: – Members if the plant kindom. – Nonchlorophyllous – Single-celled – Three body forms (spherical or coccus, rodshaped or bacillus, spiral-shaped or spirillus) – Reproduction by simple cell division.

n Fungi: – Members of the plant kingdom – Non-chlorophyllous – 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.

n Viruses: – Their categorization as plants or animals is undetermined. – Non-chlorophyllous – 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 an isometric polyhedron (shape with many sides of equal length)

n 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.

n 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.

n 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

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

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

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

n n n 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.

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

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

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

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. n Absolute control- is total control; all symptoms of pest injury are absent. n Profitable control- the level attained when monetary returns on the crop exceed the cost of the control measures. n

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

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

When using pesticides, the choice of formulation is based on: The size of the crop area being treated. n The amount of active ingredient being applied. n The other materials being applied along with the pesticide, such as other pesticides and fertilizers. n Cost n Safety n Ease of application n

n The safe use of chemical pesticides requires a respect for their toxicity. n 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. n Adjuvants- chemical additives that improve the performance of the pesticide with which they are combined.

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.

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

n 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. n Soaps- light oils made from plants; works against soft bodied insects by penetrating their outer layer and dehydrating their interiors. n Insect growth regulators- disrupt the growth and development of insects. The effect is usually hormonal and interferes with the metamorphosis of the insects.

n 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. n 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.

Eight symptoms of injury following infestation by insects: n Wilting n Color changes n Rotting n Death of tissue n Dwarfing n Increase in size n Tunneling n Holes