crop protection: chemical control by pesticides and its ...–require yearly treatments –broad...

Crop protection: Chemical control by Pesticides and its Pros and cons, Biological control: Management of plant diseases caused by fungi, Bacteria, virus, nematodes and insects; Microbial herbicides; Bacterial biopesticides;

Production of biopesticides; Fungal biopesticides; Entomo-pathogenic fungi, benefits of biological control, Integrated pest management, Maintaining virus

free plants.

Mitesh Shrestha

Principles of Control

• Exclusion – Prevent pathogens from being introduced in the first

place

• Eradication – If pathogens are established measures are taken to stop

the spread and reduce populations

• Protection – Isolate the host from the pathogen

• Resistance – Plant is equipped with disease resistance

A Pest Defined

• Technically, any organism (bacteria, fungi, plant, animal) that has a negative effect on human health or economics (food).

• Realistically, any organism we don’t want around (factors in convenience and esthetics).

Preventing Pest Attack

• Certain environmental conditions predispose plants to diseases

• Select and use adapted cultivars

• Use pest-resistant cultivars

• Plant at the best time

Preventing Pest Attack

• Provide adequate nutrition

• Observe good sanitation

• Remove weeds

• Use quality seeds or seedlings

• Prepare the soil properly

Controlling Insect Pests

• Chemical control

• Biological control

• Cultural control

• Regulatory or legislative control

• Mechanical control

• Integrated Pest Managment

Fungicides

• Protective – Protect plant surface

• Systemic – Penetrate the plant tissue

• Organic – More selective, pose less environmental danger

• Inorganic – Sulfur, copper, mercury

Other Pesticides

• Nematicides – Nematodes

• Rodenticides – Rodents

• Molluscides – Snails and slugs

• Miticides – Mites

• Aviacides – Birds

Decision making process of pest control

• Detection

• Identification

• Biology and habits

• Economic importance

• Choice of method

• Application

• Evaluation

• Record keeping

Pesticide Toxicity

• Toxicity – The relative capacity of a substance to be poisonous to a

living organism. • Oral

• Inhalation

• Dermal

• Lethal Dose (LD50) – The milligrams of toxicant per kilogram body weight of

an organism that is capable of killing 50% of the organisms under the test conditions.

Methods of pesticide application

• Foliar application

• Soil treatment

• Seed treatment

• Control of postharvest pests

Chemical Technology Problems

• Resurgences: after “eliminating” a pest, its population rebounds in even higher numbers than previous levels. Why?

• Secondary outbreaks: outbreaks of species’ populations that were not previously at pest levels. Why?

Think about mechanisms of environmental resistance on any one population.

Some Examples of Insect Food Chains

When Will It End?

Human Health Effects

• Acute: high dose, short-term response, rapid onset (headache, nausea, vomiting, respiratory failure, death). Agricultural workers suffer acute poisoning during pesticide application.

• Cronic: low-dose, long-term exposure, outcome takes many years before noticed (cancer, dermatitis, neurological disorder, birth defects, sterility, endocrine system disruption, immune system depression). Neighborhoods downwind of agricultural use; farm families; the innocent.

Environmental Effects

• Bioconcentration: – Movement against a

concentration gradient; typically fat soluble.

• Biomagnification: – Movement through the food

chain to higher trophic levels; typically persistant.

• Bioaccumulation: – Combined effect of both;

chemicals are typically fat soluble and persistant.

The DDT Case Study

• 1938; dichloro-diphenyltrichloroethane (DDT)

• Extremely toxic to insects, but seemed nontoxic to humans and other mammals.

• Cheap.

• Broad-spectrum and persistent

• Effective for disease prevention (typhus fever, malaria)

• Expanded agricultural production

• Paul Muller awarded Nobel prize in 1948

Bioaccumulation & Biomagnification

What is biological control?

• First coined by Harry Smith in relation to the biological control of insects

– Suppression of insect populations by native or introduced enemies

• Generic terms

– A population-leveling process in which the population of one species lowers the number of another

Biological Control

• Use of living organisms to reduce disease due to competition or antagonism – i.e.. ladybugs to control aphids

• The aim is to reduce dependence on chemicals

• Today emphasis on microorganisms – Bacillus thuringiensis for insect control

– Several Pseudomonas species for control of bacterial and fungal pathogens

– Numerous fungi for insects, nematodes, fungal pathogens

Why use biological control?

WHEN :

• Biological control agents are – Expensive

– Labor intensive

– Host specific

WHILE :

• Chemical pesticides are: – cost-effective

– easy to apply

– Broad spectrum

Why use biological control?

WILL: • Chemical pesticides

– Implicated in ecological, environmental, and human health problems – Require yearly treatments – Broad spectrum

• Toxic to both beneficial and pathogenic species

BUT: • Biological control agents

– Non-toxic to human – Not a water contaminant concern – Once colonized may last for years – Host specific

• Only effect one or few species

Mechanisms of biological control of plant pathogens

• Antibiosis – inhibition of one organism by another as a result of diffusion of an antibiotic

– Antibiotic production common in soil-dwelling bacteria and fungi

– Example: zwittermicin A production by B. cereus against Phytophthora root rot in alfalfa


• Nutrient competition – competition between microorganisms for carbon, nitrogen, O2, iron, and other nutrients

– Most common way organisms limit growth of others

– Example

• P. fluorescens, VITCUS, prevents bacterial blotch by competing with P. tolaasii


• Destructive mycoparasitism – the parasitism of one fungus by another

– Direct contact

– Cell wall degrading enzymes

– Some produce antibiotics

– Example

• Trichoderma harzianum, BioTrek, used as seed treatment against pathogenic fungus

Requirements of successful biocontrol

1. Highly effective biocontrol strain must be obtained or produced

a. Be able to compete and persist

b. Be able to colonize and proliferate

c. Be non-pathogenic to host plant and environment


2. Inexpensive production and formulation of agent must be developed

a. Production must result in biomass with excellent shelf live

b. To be successful as agricultural agent must be

i. Inexpensive

ii. Able to produce in large quantities

iii. Maintain viability


3. Delivery and application must permit full expression of the agent

a. Must ensure agents will grow and achieve their purpose

Coiling of Trichoderma around a pathogen. (Plant Biocontrol by Trichoderma spp. Ilan Chet, Ada Viterbo and Yariv Brotman)

Biological Control of Pests

• Pre-predator relationships

• Antagonism

• Repellents

• Alternative hosts

• Biocontrol

• Microbial sprays

Bacillus thuringiensis • Common soil bacterium well known for its ability to

produce crystalline proteins with insecticidal properties

• Since 1960s Bt available as a safe naturally occurring biopesticide

– Use as a dried inoculum containing endospores and crystals of insecticidal proteins

– used as sprays or dusts for a wide variety of insects - especially Lepidopteran

Bt Toxins • Toxins activated by enzymes in insect gut

• Kill insects by binding to membranes in digestive system and creating pores in membrane~contents leak into body cavity

• Harmless to humans, natural enemies of arthropods, and non-target organisms

Bacillus thuringiensis

• B.t. subspecies kurstaki is widely used in caterpillar control in agriculture and forestry

• B.t. subspecies israelensis is active against mosquitoes and black flies

• B.t. subspecies tenebrionis is active again beetle larvae

Bt Uses • Spray Applications

– Bt toxins degrade within a few days

– Endospores can survive for several years after spray applications

• Genetic Engineering with Bt genes

– Transfer into crop plants

– Transfer other bacteria

Pseudomonas species

• Pseudomonas fluorescens for control of fire blight (also may control apple blue mold)

• Fire blight – bacterial disease of apples and pears caused by Erwinia amylovora

• Pseudomonas out competes Erwinia

• Reduces use of streptomycin which has been helpful since many Erwinia strains resistant

• Cultural control

• Control by natural enemies

• Genetic control

• Natural chemical control

Natural Pest Control

Cultural Control of Pests • Crop rotation

– Related species and monoculture

• Sanitation

• Resistant cultivars

• Host eradication

• Mulching

Cultural Control Get rid of the alternative host!

Control by Natural Enemies

Genetic Control

• Plants or animals are bred to be resistant to the attack of pests.

– Chemical barriers.

– Physical barriers.

• Introduction of genes into crops from other species: transgenic crops (Bt)

• Sterile males are released into pest population.

http://www.bt.ucsd.edu/pest_resistance.html

Natural Chemical Control

• Manipulation of pests’ hormones or pheromones to disrupt the life cycle.

• Japanese beetle trap.

Regulatory or Legislative Control

• Plant quarantines

– Emerald Ash Borer

– Gypsy Moth

– Potatoes

Integrated Pest Management Methods

• People who practice IPM (integrated pest management) understand that eradicating insect pests and diseases of plants is usually unrealistic.

• IPM primarily consists of methods used to prevent plant problems from occurring in the first place.

Pest Management Methods

• To practice IPM in the landscape, choose plants that are well suited to the site.

• Plant them properly and keep the plants healthy by carefully watering, fertilizing, and pruning them.

Integrated pest management • Integrated pest management (IPM), also known as

Integrated Pest Control (IPC) is a broad based approach that integrates a range of practices for economic control of pests.

• IPM aims to suppress pest populations below the economic injury level (EIL).

• The Food and Agriculture Organisation of the UN defines IPM as "the careful consideration of all available pest control techniques and subsequent integration of appropriate measures that discourage the development of pest populations and keep pesticides and other interventions to levels that are economically justified and reduce or minimize risks to human health and the environment.

• IPM emphasizes the growth of a healthy crop with the least possible disruption to agro-ecosystems and encourages natural pest control mechanisms."

• IPM has been urged by entomologists and ecologists for adoption of pest control for many years.

• IPM allows for a safer means of controlling pests.

• This can include controlling insects, plant pathogens and weeds.

IPM Control Decision

• 1. Confirm that there is a pest problem – Look for pests and diseases and the evidence or signs they leave. Look for

symptoms the plant exhibits as a result of pest activity.

– Examine your plants often. Identify your plants to be sure that the twisted leaves, unusual coloration, or strange-looking structures you see are not a normal part of the plant.

– Try to rule out site-related problems by making sure that the soil type, drainage conditions, fertility level, and other environmental conditions are favorable for the plant.


• 2. Identify the problem – Effective pest management depends on the accurate identification of the

pest.

– Insects and mites often are associated with specific plants, and they follow certain development and behavior patterns as the season progresses.

– Use reference books and other resources.


• 2. Identify the problem – Plant diseases may be caused by pathogens including fungi,

nematodes, bacteria, or viruses. Each pathogen is capable of infecting only certain plants.

– Infection occurs under particular environmental conditions, with symptoms of the disease appearing later.

– To identify plant diseases accurately, compare visible signs and symptoms of the disease with descriptions in reference books.


• 3. Determine if a control measure is needed – Determine if the damage is severe enough to justify a management

tactic.

– Is the damage actually affecting the health of the plant? If not, does it make the plant look bad enough to detract from the appearance of your landscape?

– Are natural controls present?


• 4. Choose a method – Physical Methods

• Pests can be removed from plants physically.

• Use traps to catch certain pests, and barriers to protect plants from insect attack or disease infection.

• Physically removing the plant and replacing it with one that will not be affected by the pest.

• Thinning crowded plants.


• 4. Choose a method

– Cultural

• Proper soil preparation

• Proper time of planting

• Resistant cultivars

– Legislative

• Restrict transport of plant materials


• 4. Choose a method – Biological methods

• The first group includes living organisms that can kill the pest. – "Beneficials" may be predators or parasites.

– Both the larvae and adult lady beetles eat aphids and other soft-bodied insects. Other predators include lacewings, spined soldier bugs, flower flies, and spiders. Parasites live on and often kill another organism, called the host. Some parasitic wasps use caterpillars, whiteflies, aphids, and soft scales as hosts.


• 4. Choose a method continued

• The second group includes naturally occurring biochemicals that are harmful to the pest yet often are harmless to other living organisms.

– A naturally occurring biochemical is the bacterium Bacillus

thuringiensis (Bt). Bt contains a protein that is poisonous to specific insects, yet harmless to other organisms. Bt can be sprayed on plants. When the sensitive insect pest feeds on the sprayed leaves, it will ingest the protein and be killed.


• 4. Choose a method – Chemicals

• Conventional chemicals are used only as a last resort in an IPM program, but sometimes are the most effective means of control.

• To have the greatest effect, these materials need to be applied on a specific part of the plant when the pest is most vulnerable.

• Always apply chemical controls according to label directions.


• 4. Choose a method continued – Chemicals

• In many cases, environmentally safe pesticides such as horticultural oil or insecticidal soap are effective choices. Again, applications must be timed carefully to have the greatest effect on the pest insect population. Because they have no residual activity after they have dried, soaps and oils are usually the option that is the least disruptive to populations of beneficial organisms

STRATEGIES OF INTEGRATED PEST MANAGEMENT (IPM)

• Developing IPM strategies requires reliable information. Three main areas are: – Knowing pest life cycles and which management

practices disrupt or influence them to reduce pest numbers. Understanding the logic behind a management practice, rather than just doing it "because that is the way we have always done it.

– Use of a monitoring system to carefully follow pest trends to determine if a pesticide will be necessary and, if so, when it would be most effectively applied.

– Maintenance of careful records to measure the effectiveness of the IPM strategies

Principles An American IPM system is designed around six basic components:

1.Acceptable pest levels: • The emphasis is on control, not eradication. • IPM holds that wiping out an entire pest population is often impossible,

and the attempt can be expensive and environmentally unsafe. • IPM programmes first work to establish acceptable pest levels, called

action thresholds, and apply controls if those thresholds are crossed. • These thresholds are pest and site specific, meaning that it may be

acceptable at one site to have a weed such as white clover, but at another site it may not be acceptable.

• By allowing a pest population to survive at a reasonable threshold, selection pressure is reduced.

• This stops the pest gaining resistance to chemicals produced by the plant or applied to the crops.

• If many of the pests are killed then any that have resistance to the chemical will form the genetic basis of the future, more resistant, population.

• By not killing all the pests there are some un-resistant pests left that will dilute any resistant genes that appear.

2.Preventive cultural practices

• Selecting varieties best for local growing conditions, and maintaining healthy crops, is the first line of defense, together with plant quarantine and 'cultural techniques' such as crop sanitation (e.g. removal of diseased plants to prevent spread of infection).

3.Monitoring:

• Regular observation is the cornerstone of IPM. • Observation is broken into two steps, first; inspection and second;

identification.[9

• Visual inspection, insect and spore traps, and other measurement methods and monitoring tools are used to monitor pest levels.

• Accurate pest identification is critical to a successful IPM program. • Record-keeping is essential, as is a thorough knowledge of the

behavior and reproductive cycles of target pests. • Since insects are cold-blooded, their physical development is

dependent on the temperature of their environment. • Many insects have had their development cycles modeled in terms

of degree days. • Monitor the degree days of an environment to determine when is

the optimal time for a specific insect's outbreak

4.Mechanical controls:

• Should a pest reach an unacceptable level, mechanical methods are the first options to consider.

• They include simple hand-picking, erecting insect barriers, using traps, vacuuming, and tillage to disrupt breeding.

5.Biological controls

• Natural biological processes and materials can provide control, with minimal environmental impact, and often at low cost.

• The main focus here is on promoting beneficial insects that eat target pests.

• Biological insecticides, derived from naturally occurring microorganisms (e.g.: Bt, entomopathogenic fungi and entomopathogenic nematodes), also fit in this category.

6.Responsible Pesticide Use:

• Synthetic pesticides are generally only used as required and often only at specific times in a pests life cycle.

• Many of the newer pesticide groups are derived from plants or naturally occurring substances (e.g.: nicotine, pyrethrum and insect juvenile hormone analogues), but the toxophore or active component may be altered to provide increased biological activity or stability.

• Further 'biology-based' or 'ecological' techniques are under evaluation

Process

• 1. Proper identification of pest

• What is it? Cases of mistaken identity may result in ineffective actions.

• If plant damage is due to over-watering, it could be mistaken for fungal infection, since many fungal and viral infections arise under moist conditions.

• This could lead to spray costs, but the plant would be no better off.

2. Learn pest and host life cycle and biology.

• At the time you see a pest, it may be too late to do much about it except maybe spray with a pesticide.

• Often, there is another stage of the life cycle that is susceptible to preventative actions. For example, weeds reproducing from last year's seed can be prevented with mulches and pre-emergent herbicide.

• Also, learning what a pest needs to survive allows you to remove these.

3. Monitor or sample environment for pest population -

• How many are here? Preventative actions must be taken at the correct time if they are to be effective.

• For this reason, once the pest is correctly identified, monitoring must begin before it becomes a problem.

• For example, in school cafeterias where roaches may be expected to appear, sticky traps are set out before school starts. Traps are checked at regular intervals so populations can be monitored and controlled before they get out of hand. Some factors to consider and monitor include: Is the pest present/absent? What is the distribution - all over or only in certain spots? Is the pest population increasing, decreasing or remaining constant? This is done through crop scouting. Monitoring might also include the status of the water source being used for irrigation, which could potentially contaminate an area with water borne diseases or spread pests.

4. Establish action threshold (economic, health or aesthetic)

• How many are too many? In some cases, there is a standardized number of pests that can be tolerated. Soybeans are quite tolerant of defoliation, so if there are a few caterpillars in the field and their population is not increasing dramatically, there is not necessarily any action necessary.

• Conversely, there is a point at which action must be taken to control cost. For the farmer, that point is the one at which the cost of damage by the pest is more than the cost of control.

• This is an economic threshold. • Tolerance of pests varies also by whether or not they are a health

hazard (low tolerance) or merely a cosmetic damage (high tolerance in a non-commercial situation).

5. Use resources to keep up to date on IPM developments

• Researchers are always discovering new techniques, and ways to improve old techniques.

• Keeping up to date gives you the best options available to when using IPM.

6.Choose an appropriate combination of management tactics.

• For any pest situation, there will be several options to consider. Options include, mechanical or physical control, cultural controls, biological controls and chemical controls.

• Mechanical or physical controls include picking pests off plants, or using netting or other material to exclude pests such as birds from grapes or rodents from structures.

• Cultural controls include: keeping an area free of conducive conditions by removing or storing waste properly, removing diseased areas of plants properly, late water floods, sanding, and the use of disease-resistant varieties. Biological controls are numerous.

• They include: conservation of natural predators or augmentation of natural predators, Sterile insect technique (SIT).

7. Evaluate results

• How did it work? Evaluation is often one of the most important steps.

• This is the process to review an IPM program and the results it generated.

• Asking the following questions is useful: Did actions have the desired effect?

• Was the pest prevented or managed to farmer satisfaction? Was the method itself satisfactory?

• Were there any unintended side effects? What can be done in the future for this pest situation?

• Understanding the effectiveness of the IPM program allows the site manager to make modifications to the IPM plan prior to pests reaching the action threshold and requiring action again.

crop protection: chemical control by pesticides and its ...–require yearly treatments –broad...

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