Pesticide Science

Introduction-dates back to 1000 BC-Greek records show use of pesticides AD 40-90-Chinese AD 900 arsenic compounds.-Modern use dates back to 1867, when Paris green was used to control Colorado potato beetle.-Discovery of DDT in 1939, with its success lead to a new era in pesticides.-Until then insecticides used were natural inorganic compounds or plant extracts.-Sythetic organic insecticides became the most popular.-In 1941-1942, English and French scientists discovered BHC and -during the same period the Germans developed organophosphates.-Use of synthetic insecticides reached all time high in 1980s.-Increased use was as a result of several advantages of these chemicals.(Advantages and disadvantages of pesticide use.)

Definition of pesticide: Any substance for controlling, preventing, destroying, disabling, or repelling a pest.

Insecticide Nomenclature-formal process by which insecticides are named.-designated by three names

Approved common name Trade name (also proprietary name and brand name) Chemical name

Trade name-given by manufacturer or formulator of the insecticide-different names in different countries or by different companies for same formulation eg. In Zimbabwe carbaryl can be traded as carbaryl or sevin. -registered trade mark superscript indicating that a patent exist or pending and that the law protects the right of the patent holder.-In publications the symbol is used first time the insecticide is mentioned.

Common name-Once the product or insecticide is recognized it is given a common name by which it can be refered to in experimental work.-In USA,---are officially selected by the entomology Society of America and approved by the American National Standards Institute and the International Organisation for Standardization.- In Zimbabwe they are approved by the Department of Agricultural Research and Extension Services.

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Chemical name-provides the description of the insecticide structure and is formulated by following “definitive rules for nomenclature of Organic Chemistry” which are developed by International Union of Pure and Applied Chemistry.-the name means little to anyone but a chemist.-A new product or insecticide is usually identified by a code # while it is undergoing tests.

Classification of pesticides1. Based on field of usea. Household pesticides- sprays, aerosols, smoke generators, coils and rodenticides.b. Public health pesticide- mosquito control pesticidesc. Industrial pesticides- wood presevatives, pesticides in paints, antifouling chemicals in sewages, herbicides clearing railway lines.

2. Based on type of pest controlleda. Insecticides- against insect pests- natural products or synthesized.b. Herbicides/weed killers- weeds or plants growing among an economic crop.c. Fungicides- Fungal pathogens- may be fungicidal when they kill fungi or fungistatic when they inhibit fungal growth.d. Bactericides- antibiotics to control bacterial disease of plants and animals/man.e. Viricides- virusesf. Nematodes, Rodenticides, moracises (snails)g. Acaricides – ticks and mitesh. Avicides- birds

3. Based on effect on pest a. Antifeedant- inhibits feeding while insects remain on the fed plt and starving it to death.b. Antitranspirants- reduce transpirationc. Attractants- lure pests to treated locations.d. Chemosterilants- destroys pests ability to reproduce.e. Defoliants- removeunwanted plt growth within immediately killing whole plant.f. Desiccants- dry up plant parts and insectsg. Disifectant- destroy or inactivate harmful organismsh. Feeding stimulants- cause pests to feed more vigoriouslyi. growth regulators- stop, speed up, or retards growth of plant or insects.j. repellents- drives pests away without killing them.

4. Based on spectrum of activitiesa. Broadspectrum/ nonspecific- affect a range of plantsb. Narrow /selective/specific spectrum- affect/ control a few ie. At most 2 species.

Classification of insecticides5. Based on type of insect controlleda. Aphicides- control aphids

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b. Termicides- termitesc. Acaricides- ticks and mites.

6. Based on insect stage controlleda. Ovicides- against the egg stageb. Larvicides- larval stage (maggots, grubs, caterpillars)c. Adulticides- adults

7. Based on route of entrya. Contact insecticide- pest killed if it comes in direct contact with the chemicalb. Stomach poison- taken with food while eatingc. fumigants - taken in via the respiratory organs

8. Based mode of actiona. Neurotoxins- act on the nervous system after entering the insect body.b. Insect growth regulators

9. Based on chemical composition-most precise method-designated according to active ingredient.-there are three major classesa. Organophosphates-developed by Germany during world War II-OP are derived from phosphoric acid and are some of the most toxic pesticides.-are unstable in the presence of light and quickly breakdown into non toxic compounds (few hours or days).-because this reason and that they are effective they have replaced Chlorinated hydrocarbons, eg. Malathion, Dimethoate, Disulfoton-most widely used group of insecticides today.

b. Carbamates -These are broadspectrum insecticides that have had wide application in Agric.-They are produced from carbamic acid and are similar in environmental persistence to the organophosphates.-A distinct limitation in the use of carbamates in pest management is their toxicity to Hymenoptera, including pollinators and parasitoids.Two carbamates that are widely used are Carbaryl and carbofuran

Carbaryl- oldest of the effective carbamates, introduced in 1956.Has low toxicity to humans, hence it is common insecticide for use in

home lawns and gardens.Carbofuran- widely used as a soil insecticide for suppression of nematodes,

rooworms and other soil pests.-It is highly toxic to humans and should be handled with care.

Eg. Aldicarb, trimethacarb- soil insecticides Methomyl- effective against caterpillars in vegetables

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Propoxur- used by professionals against cockroaches, very effective against those in restaurants and homes thst have become resistance to OP.

c. Pyrethroids -fastest developing group of modern insecticides-replacing older insecticides because of their great effectiveness and safety of application.-these are insecticides that resemble pyrethrum (extract from flower petals of Chrysanthemum species).Compared to pyrethrum, a. pyrethroids are highly toxic to insects at very low rates.

b. quick knockdown abilityc. less recovery of poisoned insectsd. less expensivee. broken down more slowly than pyrethrum

Categorised into generations of development, the most widely used today are from 3rd and 4th generations.1st generation eg. Allethrin2nd generation eg. Resmethrin3rd generation eg. Fenvalerate (1972), permethrin (1973)4th generation eg. More potent than 3rd generation 1/10 rate

eg. Cypermethrin, flucythrinate, fluvalinate, deltamethrin.

d. Chloronicotinyls-resemble the natural product nicotine.-presently is represented by one compound imidacloprid.

-systemic and contact compound- for sucking pest-aphids, leafhoppers, thrips, white flies -termites

e. Chlorinated Hydrocarbons-oldest major insecticide class.-All insecticides in this group contain chlorine, hydrogen and carbon. Occasionally also contain oxygen and sulfur.Although effective, they are hazardous to environment and humans.

-DDT and relatives- most famous-stable and fast solubility.Others can be brokendown by animal enzymes and in the environment by

microorganisms, heat, light.HCH and Lindane (BHC)

f. Botanicals-Are insecticides derived directly from plant prducts.-expensive to extract, impractical for commercial agric.

i. Pyrethrum- by far the most widely used botanicals. It is extracted from flower petals of Chrysanthemum sp.-breakdown quickly in the presence of sunlight.

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ii. Azadiractins- extracted from seeds of neem tree, Azadirachta indica-deter insect feeding and oviposition and interfere with growth, development and reproduction.-safe- no adverse effects to human-safe with non target organisms-breakdown quickly in the presence of sunlight.

iii. Nicotine-extraction of tobacco leaves-Nicotine slfate- very toxic to insects and humans.-most dangerous of all botanicals.

iv. Rotenone- roots of legumes Derris species and Lonhocarpus sp. v. Ryania- stem and roots of Ryania speciosa a shrub.vi. Sabadilla- extracted from the seeds of Schoenocaulon officinale

Safe and effective use of pesticidesUsing Pesticides-Pesticides are some of the most potent, dependable substances.-They have also contained many of the world’s serious pest problems.-Can be hazardous to human beings and can cause undesirable effects both to agricultural and non agric ecosystems.-The cause of undesirable effects is because of the way these pesticides are used.-These side effects can not be avoided totally, but they can be minimized by proper use.

Effective use. 1.-Most pesticide use is a curative tactic.-Should be applied after assessment of pest status.

-accurate identification of the pest species-estimates of its population levels-other potential pests and natural enemies in the agro-ecosystem.

2. Choosing a pesticide- most appropriate pesticide for a given pest situation-effectiveness of the pesticide-cost of pesticide-formulations available-equipment required-time remaining until harvesting-several pests are present-effect on natural enemies and wildlife-convenience, availability.

3. Choosing a dosageAs a general rule in pest management, least is best.

-reduce pesticide dosages to be as low as possible.4. Timing of application-most important factor in efficacy and environmental safety.

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Affected by characteristics and status of the target pest.-environmental conditions- drift and evaporation.

-target the most susceptible stage.-expose population before significant injury has occurred.

5. Coverage and Confinement of application.-thorough coverage of the target area- all feeding stages-sprayers- air blast sprayers eg. Orchards and shade trees

Safe use of pesticides-personal safety begins with thorough reading of the label.

-gives explicit precautions and steps to be taken for mixing and application of an insecticide.

-gives information on disposal of containers and what to do if an accident occurs.-protective clothing-

Insect Resistance to Insecticides

Definition of resistanceResistance is the ability of certain individuals to tolerate or avoid factors that would prove lethal or reproductively degrading to majority of individuals in a normal population.

Metabolic factors are frequently implicated in the mechanism leading to development of pest resistance. If organisms especially fast breeding ones such as insect are exposed to doses of pesticides insufficient to wipe out the whole population the surviving organisms by interbreeding can give rise to a more resistant population than the original one. It is sometimes found that this greater resistance can be attributed at least in part to increased levels or efficiency of a pesticide inactivating enzymes, compared to what was on average present in the individuals of the original population. In some cases the location of a gene coding for an enzyme associated with resistance has been identified on a specific chromosome.Principles of resistance1. -Resistance in a population can be briefly explained by the same principles that explain evolution by natural selection. Briefly every biological population possesses genotypes with differential abilities to survive and reproduce in the environment. A given set of environmental conditions favours genotype with traits that are best adapted to the situation. Although several genotypes usually are present in a population at any one time, the best-adapted genotypes may be favoured that subsequently displaces the dominant ones. Natural selection sometimes called survival of the fittest or Darwinian selection is a selection of the fittest genotype for a given set of environmental conditions. This selection has led to physiological and morphological changes in biological species and has allowed for their persistence for long (geological period), despite unusual and sometimes violent changes in the environment.

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2. - Just as selections for well-adapted genotypes so do we, when we apply pest management tactics. We do this unwittingly by imposing burden, some mortality or reproductive antagonism on the pest population. Consequently the population responds as it would to natural adversaries, it adapts to overcome the burden and survive.This is something most insect populations do very well, in other words resistance is preadaptive. It is inherited from parents and never acquired through habituation of an individual during the lifetime (not caused by exposure but post adaptive). For instance it is not possible to produce resistance within a single generation by exposing insects to sub lethal doses.

3. - Resistance to pest management tactic is difficult to predict, as a general rule however the greater the population burden the greater the rate of development. A pest management tactic that causes greatest mortalities tend to be effective for a short time because susceptible genotypes are eliminated quickly and only resistant genotypes are left in the population. Once resistance is fully expressed continued application of a pest management tactic has no economically beneficial effect on a population. The rate of resistance development also depends on the genetics of a resistance factor. In most documented cases resistance originate with mutations occurring regularly in populations. These mutations result in new genotypes some of which are predisposed to resist adverse factors. If the character required for resistance can be obtained from expression of a single gene (monogenic resistance), resistance may occur only after few generation. For instance monogenic resistance for some insecticides has occurred only after few years of use eg. House flies resistance to DDT. However if many genes are required (polygenic resistance) development may be much slower.

Mechanisms of resistance to insecticidesThroughout their evolutionary history, insects have had to deal with a plethora of naturally occurring environmental toxicants. To survive in the face of these natural hazards, species have evolved a variety of mechanisms to make the materials innocuous to them. Just as these mechanisms have reduced the toxicity of natural substances, they also have reduced the toxicity of human-contrived chemicals. The result is what we call insecticide resistance. As C. F. Wilkinson stated, “insects were forewarned and forearmed to meet the challenges presented them” by modern synthetic organic insecticides. Insects deal with toxic chemicals through three major mechanisms: biochemical resistance, physiological resistance and behavioural resistance. All three mechanisms may occur simultaneously to produce the fittest animals.

a. Biochemical resistance is probably the most common type of resistance in insects. With this type of resistance the insecticide is attacked by one or more enzymes that detoxify it before it can reach its site of action. This metabolic process is often accomplished in two stages with high concentrations of mixed-function oxidases and other enzymes hat produce primary products. Although these primary products may be excreted directly, most often they undergo a secondary metabolism, forming water-soluble conjugates (covalent addition of sugar, amino acids, sulfates, phosphates and other materials) that in turn are excreted.

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b. Physiological resistance is any form of resistance that reduces toxicity through changes in basic physiology. With this mechanism, the chemical is not broken down into a less toxic form by the insect. Rather, it is accommodated by one or more physiological functions. One of the most important of these involves alterations at the site of insecticide activity. For instance, knockdown resistance in house flies to DDT and pyrethroids is believed caused by reductions in numbers of target- site receptors, making nerve sheaths less sensitive to the toxicants (a quantitave factor on numbers of receptors). In other species, cholinesterase may be altered so that they are not affected by organophosphates and carbamates. Physiological resistance may also include decreased penetration of the insecticide through the body wall. This resistance is usually conferred through modifications in composition or structure of the cuticle (for example addition of waxy layers). Other physiological mechanisms include increased rates of excretion of the insecticide and sequestering the chemical. In the later instance, lipophilic insecticides like DDT may be stored in body fat and thereby are prevented from reaching their site of action.

c. Behavioral resistance involves changes in behavior by which insects avoid insecticides. One of the best-known examples of behavioral resistance occurs with mosquitoes that vector malaria- causing plasmodia, namely Anopheles gambiae and other mosquitoes in Africa. In these species, an endophilic strain, inhabiting human structures, was susceptible to sprays of DDT applied to walls indoors. An exophilic strain not inhabiting buildings became dominant because its behavior allowed it to avoid exposure to the insecticide. Among other pests, behavioral resistance has been shown in the tobacco budworm, where resistant larvae slow their movements in the presence of pyrethroids and thus received less exposure to otherwise lethal doses.

Cross-resistance implies that an insect with resistance to one insecticide is able to resist other insecticides. For example insects that have became resistant to DDT also have cross-resistance to methoxychlor and those resistant to dieldrin have cross-resistance to heptachlor and toxaphene. This within-class cross-resistance has led to categories of resistance according to insecticide class. Some of the major classes includes 1. DDT resistance, 2. dieldrin resistance, 3. organophosphate resistance, 4. carbamates resistance, and 5. pyrethroid resistance.Although most of cross-resistance has been observed within classes, it also may exist between classes. For instance, house flies resistant to DDT have cross-resistance to pyrethrins and pyrethroids. Likewise, flies with resistance to organophosphates may have cross-resistance to carbamates. Cross-resistance usually occurs because of similar toxicity modes of the chemicals involved and inheritance of a resistance gene for that mode. DDT and pyrethroids are axonic poisons (upset impulse transmition along the nerve axon) and organophosphates and carbamates act on cholesterases.

Management of resistance

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Because of the problems associated with insect resistance, this subject has received the most attention with regards to management approaches. The development of insect resistance management is under girded by an understanding of the causes of resistance. The basic cause is an intensive mortality (or reduced reproduction) burden placed on an insect population, resulting in an advertent selection for individuals capable of overcoming the burden. Resistance can be expressed to occur against any tactic that imposes a significant population burden; the greatest question is how quickly it will develop. Therefore resistance management is mostly a matter of anticipating and slowing down the rate of development.Factors that influence rate of resistance1. Operational factors

2. Biological factors. Slowing the rate of development of resistance. The prevention of resistance to any effective pest management tactic is practically impossible in many situations.The most basic resistance management routine is use of combined tactics to achieve suppression. By integrating ecological tactics, natural enemy suppression, and resistant plants with chemical insecticides, undue reliance is not places on any one tactic. Multiple tactics place diverse pressures on the pest population, making it more difficult for the species to overcome the effects of any one tactic. More over if resistance develops to one tactic in the integrated scheme (such as insecticide resistance), its effects will be lessened because other tactics will still contribute to suppression.Another possible approach to slow resistance is to employ passive tactics in the management program, when possible. Passive tactics place no known burden on pest populations. These tactics include such measures as irrigation and fertilization to produce thrifty plants, which can better tolerate insect injury. The tactic also involves developing plant varieties capable of acceptable yields despite pest injury. When passive tactics are used, selective pressures are lessened and resistance development is less likely. Indeed these passive tactics provide the most enduring management solutions. Unfortunately, these tactics are not practical, particularly when a high-value, blemish-free produce is desired.

Resistance to insecticides. The more practical approach to slowing resistance to insecticides is perhaps to modify use patterns. There are several methods that have been suggested and employed that disrupt or significantly delay resistance in pest populations.

Chemical strategies of resistance management can be summarized as:

Management by modification.Objective: reduce selection pressure and conserve susceptible genes in the population.Advantage: Helps conserve environmental quality and natural enemies.Limitation: less practical with high-value crops and medical pests.

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Management by saturationObjective: saturate insect defense mechanisms by doses that can overcome resistance.Advantages: applicable o high-value crops like blemish-free apples and vegetables and medicinal pests.Limitation: possible adverse impact on the environment.

Management by multiple attackObjective: reduce selection pressure by imposing several independently acting forces, such that pressure from any one is below the level to achieve resistance. This is similar to using several different management tactics, only here, several different insecticides are involved. Advantages: potentially useful against pests of high value crops and medicinal pests.Limitation: imposes environmental risk, destruction of natural enemies, and risk of super resistance (resistance to several compounds at once).

Pesticide Registration

Main purpose is to ensure that pesticides when used in accordance with the directions for use, warnings, and precautions will be effective for their intended purpose while not causing unacceptable hazards to users, consumers of the treated crops and wild life or other non target organisms.In other words pesticide registration is a system by which national authority permit the entry and distribution of pesticides in their countries and consist of independent evaluation of data by these authorities on efficacy, safety to man and environment, in order to allow availability of suitable pesticides and to ensure safe and effective use.

A well devised and operated registration scheme also incorporate suitable controls, such are on product quality, packaging, manner of distribution including transportation and storage plus labeling and use of pesticide produce at the market place. Such a scheme includes recommendations of safe disposal both of product and used container.

Data required for registrationFive sets are normally required

1. Physical and Chemical properties of pesticide2. Efficacy of pesticide3. Toxicity of pesticide 4. Residues and metabolites that the pesticide leaves or may leave5. Effect of the pesticide if any to wildlife and environment

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Physical and Chemical propertiesThe identity, physical and chemical properties of the pure active ingredient. The material can be supplied in pure or technical grade or formulated product. Pure staff may be 99.9% active ingredient and is produced by chemists.Technical grade may be 80-90% ai and is supplied by the manufacturer of the product. The formulated product is one after mixing with diluent at the farm.The source, appearance and quality of the technical grade material as routinely manufactured.Identity, composition and properties of product as formulated for sale.The above is meant for quality control.

Pesticide EfficacyEfficacy is the ability of a pesticide to fulfill the claims made for it on the proposed label.It may be expressed in terms of extent of decrease of pest population occurring on the crop or the extent of development of a pest population surviving the treatment and also in terms of the protection of yield quality or quantity against damage caused directly or indirectly by the pest concerned e.g. Reduced pest population by 50%.

Pesticide efficacy test can be conducted through lab biological assays or field trials.

Pesticide Efficacy Laboratory Bioassays Bioassays are strictly experiments involving the use of living organisms to determine a pesticidal effects in a substance. The term bioassay is used in a wide sense to cover all expts where the potency of a pesticide, drug or any compound having a measurable effect on living organisms is measured using standard lab populations of suitable species.

Pesticide efficacy field trialsA field trial is a comparison of a number of plant production processes on small plots. Depending on the objective of the trial, the individual plant production processes differ with respect to type, quantity or timing of one or more production inputs or techniques while all other growth influences ie meteorological, pedological, hydrological and labour factors remain the same/equal.The effects of different variance of production inputs or techniques on crop yield or quality can be measured, weighed and observed. The differences in the results are analyzed statistically to measure whether the effects of variance differ or are the same.

Toxicity of pesticideThe study of effects of toxic substances on human being is called Public health toxicology.

Route of entryA pesticide can be taken into the body through mouth (oral), skin (dermal) or through the lungs (inhalation).

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Uptake orallyThis is minimal during pesticide application unless an operator eats, drinks or smoke before washing his hands or face.Oral poisoning has occurred when pesticide have been improperly stored in food containers especially beer or soft drink bottles; where recently sprayed fruits has been eaten or a person has deliberately committed suicide.

DermalContamination of the body is principally by absorption through the skin, particularly where they is any cut or wounds. The back of the hand and wrist absorbs more than the palm. Similarly the back of neck, feet and armpits are areas that need protection and great care must be taken to protect the eyesThe risk of skin adsorption is increased in hot weather when sweating occurs with minimal amount of effort and conditions are not conducive to wear protective clothing.

InhalationPesticides can enter the lungs by inhaling droplets or particles principally those less than 10um in diameter, or vapor but the amount is usually less than 1% than those absorbed through the skin. The greatest risk occurs when mixing concentrations or applying dust of fog especially in poorly ventilated areas e.g. greenhouses.

Residues in FoodPesticide residues is that fraction of a pesticide that as a result of its practical use has found its way into the produce or soil and is present there in the form of a parent compound or significant degradation compound or as bound residue.

Maximum residues limit (MRL)MRL is the maximum concentration of a pesticide residue resulting from the use of a pesticide according to good agricultural practice that is recommended by the Codex Alimentarius Commission, to be legally permitted or recognized as acceptable in/on a food, agric commodity, or animal feed. The concentration is measured in milligrams of pesticide residue per kg of the commodity.

Effect of pesticide on the environmentEnvironmental toxicology is the study of the effects of toxic substances in relation to the environment in which they occur. The main areas of study as far as ET is concerned are environmental chemistry and ecotoxicology.

Environmental chemistryThe registration officer looks at the physical and chemical properties of the pesticide.

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1. Vapor pressure- this will tell if the chemical is suitable for fumigation and opening the container.

2. Water solubility- movement of chemical within water and soil.3. Fate in the environment

- degradation of the pesticide in mammals and plants- degradation in the soil y microorganisms to products that are less

poisonous or even more poisonous.- Degradation in the aquatic environment by microorganisms to products

which are less or more poisonous4. Mobility in the environment

- adsorbed/desorption to the soil particles becoming unavailable to pests.- Leaching chemicals finding their way into soil water and ground water.- Volatility- how it distributes itself into water and soil

EcotoxicologyEffect of chemicals on the environment, that is on wildlife -vertebrate wildlife (mammals and birds)-non target aquatic organisms-non target soil organisms like earthworm,-how dangerous is it on predatory and parasitic arthropods

The Pesticide Container LabelInformation on the container label.3 types

1. identity of pesticides2. safe use3. effective use

Pesticide identityInformation on the identity falls under the following,

1. trade name2. purpose of the pesticide- is it an acaricide, herbicide3. names of all active ingredients and their percentages.4. Toxicology group of pesticide –colour codes5. Name and address of distributor or company responsible for marketing the

product.6. Physical nature of preparation- is it a wettable powder, liquid, solid.7. Main uses- is it used in bananas etc.8. Weight and volume of pack eg. 5kg or 500ml.9. Manufacturing lot identification.

Safe use ( Precautions)Information under safe use falls under the following;

1. Appropriate and clear indications of the degree and type of hazard using relevant warnings of risk symbols usually appear on the label eg. skull.

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2. Appropriate safety phrases to protect operators, consumers, 3rd parties, animals (domestic and wildlife) eg harmful if swallowed.

3. When the toxicity of formulated product warrant it, the symptoms of poisoning, recommended first Aid measures, the antidose (if any) and other information for physicians as required by the appropriate health authorities usually appear on the label.

4. For each use the period between application of product and sowing or planting/ harvesting, use or consumption/ sowing or planting of susceptible crops.

Effective use (directions for use)Categories include;

1. Application rate2. Time of application3. number of applications4. method of applications

Reference to information on the labelInformation on the label must be read before 1.1. buying the pesticide2. opening a pesticide container3. measuring and mixing the pesticides4. applying a pesticide5. disposing the waste (expired pesticide, excess or empty container).

Pesticide Registration scheme in ZimbabwePesticide as any chemical used primarily for the control of

-insects and other invertebrate or vertebrate pests-diseases of plants and animals-weeds-growth regulators and growth inhibitors.

All chemical products imported into Zimbabwe must conform to certain health regulations and environmental standards

Objective;-right type of chemicals are imported and safely used in Zimbabwe-ministry of Agriculture and Health are responsible for ensuring that new pesticides products are tested for their efficacy and toxicity for a period of three years.-The registration process is largely concerned with hazard assessment and concern for human and environmental safety.Health safety standards refers to safe use, storage and disposal.Registration is done to ensure safe and efficient use of pesticides in the interest of:

User – who is concerned with the efficacy of the material and its hazards in handling.

The consumer- who is concerned with possible residues in food.

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The general public- who is concerned with such hazards as drift, contamination of waterways and loss of wildlife.

The vendor- who should be protected from unsound or unfair claims from competitive products.

Legislation1. There is an Act which prohibit the sale or distribution of pesticides unless they are

registered by Ministry of Agriculture with the Plant Protection Research Institute in the Dep’t of AREX. Fertilizer, Farm and Seeds and Remedies Act (Chapter 186, Section 24). -defines and establishes the regulations and process of registration, experimentation, storage, distribution, labeling and selling of pesticides.-Ensures that only the right type of chemical is imported into Zimbabwe.

2. Hazardous substances and Articles Act (Chapter 322, Section 47) this act is administered by Ministry of Health.-emphasis is on labeling, proper use of hazardous substances and proper handling. -the act requires that all hazardous substances should be classified on how hazard they are.

3. Protective Clothing: General regulation, 1984-defines and specifies the conditions for safe use, application and handling of pesticides.-It requires that people must be provided with safety clothing before use of these hazardous products.

The Registration Process2. Requirements

a. For any pesticide to be considered for registration in Zimbabwe that pesticide must be registered in the country of origin

b. Registration must be done by a resident representative of the company that manufacture the product who will then market the product in Zimbabwe.

Application should be submitted in triplicate to the registering officer.Attached should be:

Three copies of the proposed label The text of any advertisement to be used to promote the sale of

the pesticide Two samples of the pesticide- the amount being specified by the

Registering Officer. Information on efficacy and toxicity.

Registration is completed when the applicant is issued with a certificate of registrationIf applicant is refused permission he/she is free to appeal to the ministry of Agriculture within 50 days of being notified of the refusal.

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3. Colour categorizing of pesticides

The Registration Officer assigns a colour code to each commercially available pesticide based on mammalian toxicity as indicated by:

Acute oral LD50 of the technical material- this data will be taken from the Pesticide Manual published by the Crop Protection Council. The oral LD50 is that single dose expressed in mg/kg of body weight which when given by mouth kills 50% of the animals under test.

The strength of the formulation The persistence of the material after application Other relevant data

Purple - Acute oral LD50 of up to 100.- may only be sold to someone whose business, profession or trade require

them- may only be offered for sale by licensed dealers where part of premises is

set aside for the sale of dangerous substances.- dealer must keep a register of all sales of this group of pesticide, each sale countersigned by the purchaser or his nominee and the firm’s license number noted. - the product must be enclosed and locked wherever it is stored.- Have a skull and crossbones within a purple triangle- words “V. DANGEROUS Poison” appear beneath the triangle.

Red - Acute oral LD50 of between 100 and 500- Use should be generally restricted to horticultural, agricultural, health or

industrial pest control operations. - May be sold by a licensed dealer, with a special part of premises set aside

for the storage and sale of dangerous substances.- must not be bought from supermarkets- skull and bones and its written DANGER.- Word “Dangerous Poison” beneath the base of the triangle.

Amber (Orange)

- Acute oral LD50 of between 501 and 2000 - Can be used without danger in home gardens and for external use about

the home.- can buy them from the supermarkets.- Skull and bones and word Danger appears within the amber triangle.- Word “Poison” beneath the base of the triangle.

Green -acute oral LD50 of over 2001 mg/kg of body weight

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-can be used without danger in homes/ as admixture to grain or other stored produce for human or animal consumption.-can be sold by any shop or store.-word “Caution” within a green triangle -words “ Harmful if swallowed” beneath the base of the triangle.

Integrated Pest ManagementApplication of technology, in the context of biological knowledge, to achieve satisfactory reduction of pest numbers or effects. -technology aspect includes such tools as insecticides and equipment used to apply them.-Biological knowledge of pest-allows us to know where, when and how to apply the technology.

Historical Highlights of pest technologyCan be divided into three eras:

1. Pre-insecticide era2. Insecticide era3. Pest management era.

Pre-insecticide eraControl of pests was based on natural compounds like botanicals.Equipment for pesticide applications was developed.Application was not effective

Insecticide eraDiscovery of chemicals such as DDT----- Organophosphates--------Carbamates----------Pyrethroids.Problems of resistance.1960s detrimental effects of insecticides were felt, residues found in food, environment, development of resistance.

Emergence of pest managementBecause of problems of resistance, replacements and resurgents people were moving back to pre-insecticide methods, integrated control such that natural enemies can be preserved.Pest management differed in its holistic approach, its sythetic ideas, inclusion of basic population theory in its design.On this approach emphasis was on economic threshold levels.

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The Concept of Pest ManagementDefinition and characteristics of pest management Pest management can be defined as a comprehensive pest technology that uses combined means to reduce the status of pests to tolerable levels while maintaing a quality environment.This definition carries with it several implications that set pest management apart from other technologies.

1. First it seeks to deal with pests in the context of whole production system rather than as a separate collection of individual systems. It proposes that several technologies be employed to alleviate problems rather than relaying on a single tactic eg. Insecticides alone.

2. The objectives of pest management are also clear from the definition. The main objective is to reduce pest status. Although reducing status can be achieved by killing pests, killing certainly is not the objective, preventing the economic loss is. Indeed pest status also may be reduced by avoiding or repelling pests or reducing their reproductive rates.

3. Another implication of the definition is that pest populations or their effects should be reduced to tolerable levels. In this instance, tolerance means that humans should accept the presence of pest species, although at levels that are not economically important. This aspect admits that complete elimination of pests may not be feasible or even desirable. This acceptence of pest presence sets pest management apart from pest control.

4. Finally the most important objective of pest management is the maintainance of a quality environment. This objective clearly refers to conservation and it includes quality of both cropping and non agricultural environment (air, water, soil, wildlife and plant life). With pest control approach, environmental quality was largely ignored except for attention paid to crop vigor and soil elements supporting the crop.

The principle of pest management emphasize that cropping systems behave similarly to unmanaged or natural systems, that is they have a diversity of interacting elements like natural insects and weed elements that influence the ecology of the crop environment. By maintaining the quality of this environment lasting solutions can be achieved.

Pest Management StrategiesA pest management strategy is the overall plan to eliminate or alleviate a real or perceived pest problem. The particular strategy development depends on the particular life system of the pest and the crop involved.In addressing problems using pest management, we aim to reduce pest status, this is determined by both the insect and the crop. Our management program hence may emphasize modification of either or both of these. Therefore several types of strategies might be developed, based on economics and pest characteristics:

1. Do nothing.2. Reduce pest population numbers3. Reduce crop susceptibility to pest injury,4. Combine reduced population numbers with reduced crop susceptibility.

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After strategy has been developed, the methods of implementing the strategy must be chosen. These methods are usually called tactics. Optionally several tactics are used to implement a management strategy.

Do nothing strategyIt is possible that insect injury only seems as if it is causing a loss, when in reality the crop species tolerates the injury without economic damage. The phenomenon of mistaking trivial insect injury for economically significant injury occurs all too often and is usually the result of not assessing population density in relation to the economic threshold. When pest populations are below the economic threshold, ‘do nothing’ definitely is the strategy to follow; otherwise, more money is spent on management than is gained in utility. The most frequent need for the ‘do nothing’ strategy usually arises when insects cause indirect injury. This strategy may also be the ultimate one following a successful pest manament program

Even though tactics are not implemented in this strategy it does not mean that little activity is involved is involved or that pest suppression is not occurring. Considerable sampling is required to assure that taking no action is appropriate, and significant pest suppression may have occurred as a result of natural environmental factors.

Reduce numbers strategyReduced insect numbers to alleviate or prevent problems is probably the most widely used strategy in pest management. This strategy is usually employed in a therapeutic manner when densities reach the economic threshold or in a preventative manner based on the history of problem.The tactics utilized in the reduction of the number strategies are many and varied. Most of these increase the mortality in pest populations by creating or intensifying hazards to insects in their environment. Hazards are increased with tactics such as natural enemies, insecticides, many resistant cultivars, ecological modifications, and insect growth regulators.Other tactics attempt to reduce numbers by reducing reproductive rates in pest populations. Some of these include release of sterilized insects and application of chemicals that disrupt mating activity.

Reduce crop susceptibility strategyReducing crop susceptibility to insect injury is often one of the most effective and environmentally desirable strategy available. For this strategy, the pest population is not modified at all. Rather we rely on changes made in the host plant that renders it less susceptible to an otherwise damaging pest population.The tactics involved in the reduce crop susceptibility strategy usually involve elements of host plant resistance and ecological management (crop environment manipulations).Some of the tactics in ecological management for reduce crop susceptibility are improving plant vitality through fertilization and charging planting dates to upset the synchrony between a pest and a susceptible plant stage.

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Combined strategy The remaining and perhaps the most obvious strategy is one that combines objectives of all previously mentioned strategies to produce a pest management program with several tactics. In many ways, this is the most desirable strategy when feasible.

Kinds of pests and likely strategiesThe appropriate strategy and subsequent complexity of a pest management program is primarily determined by the status of a pest in the production system. Four pest types may be designed according to status. The type include noneconomic (subeconomic), occasional, perennial, and severe pests.

Subeconomic pests These insects are pests in a true sense, even if they cause insignificant losses. The GEP with this pest type is far below the economic injury level, and the highest pest populations fluctuations do not reach that level. Attempting to reduce injury from such pests would cost more than the losses they inflict.

Occasional pestsThis is the most common type of the pest. It has a GEP substantially below the economic injury level, but the highest fluctuations exceed this level occasionally and usually sporadically. This pest may be present on a crop most years but, does not cause economic damage.A wait and see attitude is assumed, with reliance on early detection, prediction of impending outbreaks, and employment of tactics only when the economic threshold is reached. The objective is to dampen outbreak peaks, with no efforts towards reducing the GEP.

Perennial and severe pestsThese are the most serious and difficult problem pests in crop production. Only a few insects belong in these categories, and often referred to as key pests. Problems created by these pests are usually caused by relatively high market value of the crop and/ or very dense insect populations. In this category are insects and other arthropods that attack the harvested produce directly and those that almost always occur in great numbers. Some of the worst pests may cause only blemishes on produce, making it unacceptable to consumers and resulting in serious economic losses.With perennial pests, the GEP is below but close to the economic injury level that economic injury occurs in more years than not. Only infrequently do population peaks of this pest type not reach the economic injury level.Severe pests have a GEP that is actually above the economic injury level, making them a constant problem.

Development of a pest management program.(read)

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Insecticide formulations(read)

Application of liquid pesticides formulations

Components of a sprayerTank, pump and nozzle

Spraying equipment

Ground equipment1. Knapsack sprayer-it can be fitted with a lance or a boom. Boom can be a vertical

boom (tail boom) or a horizontal boom.Carried on the back.

2. Hand carried sprayersa. Battery operated spinning disc sprayerb. Motorised fan assisted spinning disc sprayer.

3. Tractor mounted sprayersa. Boom sprayer – can be fitted with hydraulic nozzles or spinning cupsb. Mist blower - it is almost like a fan assisted- can have hydraulic nozzles

or spinning cups.

Aerial sprayersType of aeroplane used

1. Fixed wing- very fast speed2. Rotary wing (helicopter)- slow can manauver its way in terrains.

Selection of spraying equipment

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Pest ControlApplication of technology, in the context of biological knowledge, to achieve satisfactory reduction of pest numbers or effects. -technology aspect includes such tools as insecticides and equipment used to apply them.-Biological knowledge of pest-allows us to know where, when and how to apply the technology.

Insect Pest controlThe control of insect pests (arthropods)

1. Legislative control.Legal enforcement of certain control measures, or inspection procedures aimed at regulating the spread of pests from one area (region, country or continent) to another.Involves: Quarantine, Eradication, Certification and Rotation orders.

a. Quarantine. Quarantine laws allow for inspection at the point of entry of all products that might harbour foreign pests. These laws also enforce strict isolation of any species imported for study (eg. for biological control research).Unfortunately it postpones the entry of pests.

b. Eradication.Serious pests may be subject to a ‘notification order’, whereby any farmer who suspects that the pest may have appeared on his/her crop must notify the appropriate authorities, who then undertake pest eradication. The Colorado beetle in Britain falls into this category.

c. Certification.Certain plants, seeds, tubers, etc., subject to particular pests may not be sold unless free of the problem. These pests include greenhouse whitefly in Britain.

d. Rotation orders.Rotation is among the cultural practices, which have been subject to legal enforcement in various countries at various times. (eg. sugar beet rotation to control beet eelworm in Britain).

2. Cultural Methods.These are simple farm or agricultural practices that man has learnt by his long experience as a farmer in order to keep the pest populations down. These methods act bests as prophylaxis rather than a complete cure (control) therefore are suitable when used alone for low-unite-value crops. This method costs nothing except labour, and are convenient and without hazards.

a. Crop Rotation.

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Same crop is not grown successively on the same field. This is effective if the preceeding crop pest would not affect those of the following ones. Crop rotation normally reduces and delays attack rather than giving complete control because, although control may be significant within a given field, it is less restraint over an area as a whole. Most pests have strong migratory powers or, if not, can survive rotation on wild host plants. Affects those insects that have limited host range (eg. serous insect pests of the maize, wheat and red clover rotation only three are important pests of all three crops) and are relatively immobile in the stage of their development. Eg. Soil-inhabiting pests (wireworms, white grubs, ahfers, leatherjackets and shoot-boring flies), which multiply most successfully under grass. The various crop midges (eg. pea midges and bladder pod midges) are weak fliers and also are affected by crop rotation.

b. Crop Location. Crops from adjacent fields should be chosen such that the pest(s) of one crop may not be attracted by those of the other. Mixed crops would produce the same effect.

c. Sanitation.Farm hygiene often has a pest control purpose. The destruction of crop residues removes residual pest populations (eg. stalk-boring grubs in maize) and eliminates plant debris on the soil surface in which many pests find shelter for hibernation (eg. flea beetles and whiteflies of brassicas). Destruction of crop residues of cotton followed by a gap before cotton is planted again is mandatory in many countries, including Zimbabwe. It is effective against the bollworm Platyhedra since this pest does not have any wild host to maintain the species if the crop population is destroyed. In banana and cocoa, pests often breed in fallen, rotting leaf or stalk material, and both fruit flies on the coffee berry borer often infest new fruits after emergence from fallen fruits on the plantation floor. The destruction of weeds acting as reservoirs for pest populations is often recommended. In cotton, nearby free growing cotton and related weeds (Malvaceae) should be eliminated to reduce populations of the cotton-stainer bug in cotton fields. Weeds outside the farmer’s boundary are just as important as those within.

d. Pruning and Thinning. Occasional pruning of the old, damaged and weak portions of the plants (or the trees) encourage growth of new shoots, which are healthier and pest resistant. The removal and destruction of infected growing plant material where there is danger of spread to other parts of the crop can be used to control pests. Before the advent of adequate plant resistance to the pest, the control of reversion virus spread by the black currant gal mite was largely dependent on the removal and burning of infested bushes; rouging plants attacked by the sisal weevil are still a component of control of this pest in the tropics.

e. Soil manuring and Fertilisation.Vigorous, healthy plants are less attacked by pests. This is achieved in four ways:i. Rapid growth shortens any susceptible stage. It therefore induces resistance

against pests such as stem borers, cut worms to which seedlings have a relatively short window of susceptibility before tissue hardens.

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ii. It may lead to the maximum expression of some chemical resistance factors.iii. It will allow maximum compensation for damage by the plant. For example,

good root systems would clearly withstand root grazing by pests where weak root system will not. Another example, the shothole borer (Xyleborus fornicatus) on tea in Sri Lanka, where damage was successfully reduced by fertilizing the bushes with nitrogen. The stimulation in growth enabled the bush to form new tissue as a support bracket over the beetle gallery so that breaking of the branches at the gallery as tea pluckers passed through the plantation no longer occurred.

iv. It can promote uniformity and density of the crop stand. This can discourage pests such as chinch bug (Blissus leucopterus), which is abundant where the crop stand is somewhat thin. Aphids occur in small numbers where the crop is more dense, this is because fewer winged immigrants land where less bare ground is exposed.

However, just as fetilisers produces a more nutritious plant for man, so many insects may also benefit. Aphids, leafhoppers, mites, thrips and leaf-mining grubs have all been found to breed or develop more rapidly on plants given good nitrogen fertilization. By contrast, there is some evidence that manuring with potassium and phosphate may reduce the incidence of some pests, and with aphids, which are sap feeders, good potassium fertilization can reduce nitrogen available in the sap without impairing the value of the leaf protein. f. Soil Cultivation Many insects live and hibernate in suitable temperature and humidity conditions relatively near the soil surface. These conditions can be disturbed by ploughing.

This tends to reduce soil insects and those, which pass any of their developmental stages under the soil.

i. burying and exposing (to full radiation of the sun and predators) a developmental stage (larvae and pupae) of the pest. Eg. white grubs (beetle larvae pest), other pupae and eggs may be buried to a depth from which they fail to reach the soil surface after emerging.

ii. Other pests may be killed mechanical by rough contact with soil clumps; root aphids (eg. cereal root aphids) will suffer from break-up of the ant colonies, which tend them.

iii. Changing physical conditions (pH, moisture or oxygen content) of the soil. Compacting the soil with rollers is a cultural method for limiting the between-plant movement of some larger soil insects such as beetle larvae.

iv. Eliminating the alternative host plants. The stem-boring frit fly develop large populations in grasses and migrate into winter wheat seedlings, but problem is never serious when lands are ploughed in late summer and left fallow until the sowing of wheat.

v. Increasing growth and vigour of crops.

g. Growing resistant or tolerant plant varieties.

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This involves growing crop varieties that are less vulnerable to attack than others or which yield well in spite of attack. Resistance of the plant to insects is a property that enables it to avoid, tolerate or recover from injuries inflicted by insect populations that could cause damage to other plants of the same species under similar conditions. This property is generally derived from certain bio-chemical and/or morphological characteristics of the plants, which affect the behaviour and/or metabolism of insects so as to influence the degree of damage caused by them. The property of resistance is developed by selective plant breeding.

h. Trap Crop.Small planting of a susceptible or preferred crop (eg. kale for certain bug pests of cabbages) maybe grown near a major crop to act as a trap. Pests accumulated on this trap may then be killed by suitable means, insecticides, or ploughing or feeding the crop to animals or the use of flame gun. Such concentrations can also be induced by position (eg. edge rows for swede midge); by exploiting the crop zone in which most insects are deposited behind windbreaks; by planning taller plants at the edge of the crop to filter out flying insects, by early sowing (eg. against corn earworm).

3. Biological Control.This is the employment of any biological agent (natural enemies) for control of a pest.Or can be defined as tactic involving purposeful natural enemy manipulation to obtain a reduction in a pest’s status.Natural enemies of pests, are living organisms found in nature that kill outright, weaken them and thereby contributing to their premature death or reduce their reproductive potential. A natural enemy usually reduces the subject insect pest population, the host or prey, by feeding on individuals, thereby promoting its own population at the expense of the population fed upon. Not only do these natural enemies help prevent some insects from attaining pest status, but they also play a role in reducing the damage potential of significant pests. Established pests, as damaging as they may be, would cause even more damage were it not for the presence of natural enemies.Virtually all insects’ populations are affected to a greater or lesser extent by natural enemies.

Classical biological control.The theory of classical biological control is actually not different from that in ecology and population dynamics. Many environmental factors regulate population density, thereby keeping insects within certain bounds of fluctuation. These include density-dependent and perfectly and imperfectly density-independent factors.In the context of biological control, pest population is one being regulated, and natural enemies as imperfectly density-dependent factors responsible for that regulation. The objective of biological control is either to introduce natural enemies or manipulate

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existing ones to cause to cause the pest population to fluctuate (be regulated) at a density below the economic injury level.A goal of many of these biological control programs is to establish a self-sustaining system. For example, a natural enemy is introduced in an area with hopes that it will become established, cause the pest population to fluctuate below economic injury level, and continue to hold the density down indefinitely without further manipulation. This strategy does not mean total elimination of the pest in an area because achieving that would also mean elimination of the food supply for the natural enemy.The mechanism for the self-sustaining system, in theory, is based on food supply for reproductive capability of the natural enemy. An increasing pest population provides plenty of food for the natural enemy, and natural enemy population expands. As expansion occurs, an increasing proportion of the pest population is destroyed, reducing food for the natural enemy. This food shortage worsens until natural enemy reproduction rates decreases, causing a downward trend in enemy population numbers. As natural enemy numbers fall, less pressure is placed on the pest population, and pest numbers turn upward, followed by an increase in natural enemy numbers.

Agents of biological control.i. parasites. A parasite is an organism that lives on or within a larger organism, its host. The parasite feeds on its host, usually weakening it and sometimes killing it. A parasite requires only one or part of one host to reach maturity. Frequently there are many parasites in a single host. Parasites with greatest impacts on insect populations are insects and nematodes. Mites also parasitize insects but have lesser impact on host population.

ii. Parasitoids.Insects that parasitize other insects are most appropriately called parasitoids. A parasitoid is parasitic in its immature stages but is free living as an adult. In all instances the parasitoid kills their host, but in some instances, the host may live much of its full life before dying. Parasitoids may attack any host stage, but the adult stage is the least frequently parasitized.Six orders of insects have been listed as parasitoids. These orders include the Coleoptera, Diptera, Hymenoptera, Lepidoptera, Neuroptera and Strepsiptera. However by far the most important of these are the Hymenoptera and Diptera, in that order. Parasitoids either penetrate the body wall and lay eggs insider the host or attach eggs to the outside of the body of the host, the newly emerged larvae then burrow inside or somehow breaks through the host’s exoskeleton to feed.

iii. predators.These are living organisms that feed on other organisms, their prey, sometimes devouring them completely and usually rapidly. Predators may attack prey both as immatures and adults, and more than one prey individual is required for a predator to reach maturity.The most important predators for biological control programs have been insects and mites.iv. pathogenic microorganisms.

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Just like people and other animals, insects contract diseases, and natural populations are often strongly influenced by diseases. The major microorganisms causing diseases in insects include bacteria, viruses, protozoans, fungi and rickettsiae. They may cause diseases that kill insect outright, reduce their reproductive capabilities or slow their growth and development.Most of these microorganisms have been used or studied for use as microbial insecticides. Microbial insecticides are biological preparations that are often sprayed or delivered in ways similar to those of conventional chemical insecticides. The various formulations include baits, dust, granules, and must be registered.

Advantages of biological control.

1.The technique is selective with no side effects. Biological control agents tend to be fairly prey specific, and do not carry the kind of environmental dangers associated with insecticides. This does not mean that side effects can be totally excluded, although they have been very rare in the history of biological control. On one occasion a serious disease of sugar cane was introduced into Trinidad on the ovipositor of a parasitic insect being brought in for biological control purposes, and there have been at least two cases where, after controlling the intended prey, biological control agents have switched to other related herbivores, which were important in controlling weeds. Some kinds of side effects on other insects are almost inevitable; the success of the parasite against cassava mearlybug has resulted in a decline of the ladybird predators of the mearlybug, because the parasite caused such a dramatic reduction in their food supply. 2. Biological control is cheap. It is far less than the cost of developing an insecticide and also this cost only has to be met once. Moreover it is usually free of charge as far as the farmer is concerned and may be the only economic solution for some forestry and pasture problems, and for many tropical crops grown which have low inputs and are unable to carry the cost of insecticides.

3. Biological control agents are self-propagating and self-perpetuating. Ideally, once introduced, biological control agents will persist in time and may spread over large areas from the points of realize and reach targets that chemicals cannot (such as larvae concealed in fruit, stems or underground.

4. The development of resistance of pests to biological control is unlikely. Although insects are often capable of defence against attack by carnivores and may, for example exhibit escape behaviour, release repellent chemicals and encapsulate foreign bodies such as parasite eggs, an existing natural enemy of a pest is clearly adapted to such behaviour and is moreover, capable of further adaptation. Disadvantages of biological control.

1.Biological control limits the subsequent use of pesticides. Where biological control agents are being used against one pest, it is clearly difficult to continue using insecticides against other pests on the same crop. This may make the use of biological control

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impossible unless biological control systems can simultaneously be set up against other insect pests.

2. Biological control acts slowly. It takes some time for biological control agents to spread from their points of release, to built up in numbers and make their impact on the pest population. During this period, the pest may still be present at intolerable levels; any use of pesticide against it or other pests on the crop can endanger the biological control system.

3. Not an exterminant. A biological control system, if intended to be self-perpetuating, involves the presence of the prey even if only at low levels. Growers therefore cannot expect to have a totally clean crop as they can with insecticides, and there may be several types of pests (eg. Blemishers of quality, disease vectors) which even low levels, will cause economic damage.

4. Biological control can be unpredictable. The grower has relatively little control over a biological control system, and this might worry him. Even working programmes can suddenly fail. The ladybird (Chilocorus cacti) was released against mulberry scales in Puerto Rico in 1938. The control was successful, but over a long period the ladybird virtually exterminated the scale and then died out itself. This resulted in a sudden mass outbreak of scale recurred in1953. Similarly, in the biological control of whitefly in greenhouses, a sudden change in weather or a period of extreme hot or cold can cause a breakdown of the system. Techniques of biological control.

i. Introduction Introduction also known as importation, is often considered the ‘classical’ practice in biological control because most early programs used this approach.The basis for this practice is to identify the natural enemies that regulate a pest in its original location and introduce these into the pest’s new location: thus, natural enemies are reassociated with their prey and host. The hope is that the natural enemies, once introduced, will become established and permanently reduce the pest’s general equlibrium position (average population levels) below the economic injury level.Successful examples includes, introduction of;

1. vedalia beettles to control cottony cushin scales.2. citrus blackfly Aleurocanthus woglumi controlled by a wasp parasitoid

Eretmocerus serius. ii. Augmentation Augmentation is a biological control practice that includes any activity designed to increase numbers or effect of existing natural enemies. These objectives may be achieved by releasing additional numbers of a natural enemy into a system or modifying the environment in such a way as to promote greater numbers or effectiveness.Releasing additional numbers of natural enemies is similar to the introduction practices, except that augmentative releases are expected to result only in temporary (usually one

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season or less) suppression. Therefore the ecological result is most likely the dampening of pest population peaks, rather than significantly changing the general equilibrium position. Because of their temporary effect, these releases must be made periodically.These periodical releases may be considered as either inundative or inoculative. iii. Inundation releases.These releases depend on propagation of massive numbers of natural enemies and their widespread distribution. Subsequently, the release of the actual enemies suppresses the pest population, either little or no impact expected from progeny of the released individuals.Examples include:Control of Europian corn borer with Trichogramma species.In many instances, however inundative releases of insect predators and parasitoids have been unsuccessful. The lack of success is usually ascribed to insufficient coverage over a greater enough area or augmentation in environments not supportive of the numbers released. Another reason is the movement of released natural enemies out of the targeted area.Some of the most successful inundative releases have been with pathogenic microorganisms like B. thuringiensis. Microbial insecticides have been applied mostly against caterpillars (Lepidoptera), beetles (Coleoptera), mosquitoes, and black flies (Diptera), they suppress a pest population quickly, much the same way as a conventional insecticide. After the initial impact of the release little subsequent suppression can be expected.

iv. Inoculation releases. These releases differ from inundative releases in that, once they occur, the natural enemy is expected to colonise and spread throughout an area naturally. An inoculation is often made only once in the growing season, and the progeny of the released individuals have the most significant impact on the pest population. Some of the most successful programs utilizing this approach with predators and parasitoids have been reported from field and greenhouse crops in China and Russia.

v. Conservation Probably the most widely practiced form of biological control is conservation of natural enemies. The objective of conservation is to protect and maintain these existing populations, particularly the insect predators and parasitoids, in an agroecosystem. Basically, this approach requires knowledge about all aspects of the natural enemy community, including species present, population numbers, phenology, and impact of pest population. With this knowledge, crop production activities, including existing pest management practices, are modified to avoid natural enemy destruction.Methods to conserve natural enemies may include less frequent moving of field edges and clipping alfalfa in strips at different times to maintain habitat and alternate food source for their populations. Perhaps more important as a conservation approach is use of insecticides in a way that will avoid natural enemy mortality. This method usually includes using chemicals less toxic to natural enemies, reducing numbers of applications and reducing dosage levels.

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Nematode control.

1.Cultural control. The bases for this method were simply to deprive the pest of a suitable host plant. This practice is still the major component of nematode control.

i. Crop rotation.Still forms the base for cultural control. Use of non-hosts, resistant or immune hosts, tolerant hosts and poor hosts are central.Planting with known non-host grasses plays a critical role for root-knot control in tobacco and tomatoes. Examples of these non-host grasses are:

Ermelo weeping lovegrass (Eragrotis curvula cv Ermello).Umgeni weeping lovegrass (Eragrotis curvula cv Umgeni),Katambora Rhodes grass(Chlori gayana),Sabi panic grass (Panicum maximum).

ii. Resistant hosts.Plant breeders continue to breed resistance to nematodes into susceptible crops. Resistance to root knot nematode already exists in certain cultivars of tobacco and tomatoes. In addition, many citrus rootstocks are resistant or are poor hosts to citrus nematodes.

iii. Flooding.Flooded soil will help control nematodes by creating essentially anaerobic conditions, but to be effective, soils must be flooded for long periods eg. greater than 6 months. This technique has little practical value in intensive agriculture especially where water is a limiting factor.

iv. Fallow.Leaving the soil fallow, free of any crop and weeds will cause a reduction in nematode numbers especially in hot, dry climates. In area where wind or water erosion occurs, this also is not effective.

v. Catch crop.Roots of common marigold and also the tall khakhi weed Tagetes minuta stimulate active penetration of root-knot nematode but does no support it, this results in the nematode dying.

vi. Heat

a. Heat treatment of plant material.This control nematodes in plant materials that are usually dormant or relatively resistant plant stages, eg. bulbs, nursery material, seed, etc. This practice is dependent on the

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nematode being more sensitive to the procedure than the plant tissue. The plant material is dipped into hot water, raising the temperature of this material rapidly to about 45-500C and maintaining it for about 20-25 minutes.

b. Soil solarisation.A thin, clear polyethylene sheet is placed over exposed, well-cultivated soil to trap the solar energy in the soil. This procedure is most effective in hot climates in summer months. The sheet must be leveled tightly over the soil for a period of 4 to 8 weeks, allowing temperatures in excess of 500C to develop in the top few centimeters of soil.

c. Steam treatment.This involves the application of heat; usually steam to small quantities of soil to sterilize that soil. This method involves a very high capital cost and high inputs and is only used in large and concentrated horticultural industries. The method has drawback in that it removes the also beneficial organisms in soil, like mycorrhizol fungi that consequently have to be artificially re-introduced.

2. Quarantine.The exclusion of nematode pests by effective quarantine practices plays an important role both on a national basis and within intensive self-contained environments eg. glasshouses and nurseries. This involves plant materials being inspected and cleared before being used.Sound hygienic principles in nurseries are also important in limiting the spread of nematode diseases. In order to be effective, all root media must be sterilized, irrigation water must be purified and access to all nursery restricted.3. Biological Control.Present in many soils are a range of organisms that have the potential as biocontrol agents of nematodes. These include viruses, bacteria, fungi, predacious nematodes, protozoa and mites.

Examples,a. nematode destroying fungi, acting either as endoparasitic fungi infecting the

nematode internally certain cyst nematode populations are regulated this way, or predacious fungi that trap and kill active nematodes in the soil.

b. Endoparasitic bacteria, eg. Bacillus penetrans, an organism frequently found infecting nematodes.

c. Soil living mites.

4. Chemical control.Use of nematicides such as methyl bromide; ethylene dibromide (EDB); 1,3 dichloropropene (DD); EDB + chloropicrin mixtures; methyl bromide + chloropicrin mixtures.

Control of plant diseaseAvoidance or evasion of pathogen

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-several methods are used in an attempt to evade pathogens. This type of control helps to avoid the interaction that is suitable for an epidemic.

1. Choice of geographic area-choose an area where disease risks are not too high.eg. (a) Anthracnose (Colletotricum lindemuthianum) and bacterial blights (Xanthononas phaseoli and Pseudomonas phaseolicola) are seedborne diseases favoured by high humidity.In dry, irrigated areas the conditions of low humidity are unsuitable for these pathogens, and therefore the plants and the seeds are likely to be free of them. (b) to produce potato seed tubers free of viruses, potatos are grown in cooler and higher altitude areas where aphids the vectors of these viruses are absent or their populations are small and can be easly controlled.

2. Choice of planting date, either late or early plantings. This helps you to avoid or escape infections by avoiding the favorable interaction of disease components. eg. (a) early planting in the control of soyabean rust in soyabeans, by planting early November you avoid exposing the most susceptible stage of the plant (flowering and pod filling) to disease which usually sets in between February and March. (b) early planting of tobacco to reduce problems of tobacco bushy top disease.

3.Use of disease free planting material for example, vegetative propagated materials such as buds, root stocks, tubers, pathogen free seed.

4. Modification of cultural practices for example proper distance between fields to prevent spread of pathogens. Avoid overlapping susceptible crops.

Exclusion of the pathogen As long as plants and pathogens can be kept away from one another, no disease will develop.1. Treatment of planting materials or seeds. This increases the chances that the host will remain free of the pathogen or go through its susceptible stage before the pathogen reaches the host.

2. Quarantine, inspectionWhen plant pathogens are introduced into an area in which they did not previously exist, they may cause much more catastrophic epidemic pathogens. Acts that prohibit or restrict entry into or passage through the country of plants, plant products, soil, and other materials carrying or likely to carry plant pathogens not known to be established in this country.

3. Crop CertificationSeveral voluntary or compulsory inspection systems are in effect in various states in which appreciable amounts of nursery stock and potato seed tubers are produced. Growers interested in producing and selling disease free plants submit to a voluntary inspection or indexing of their crop in the field and in storage by the state regulatory agency, experiment station personnel or others. If, after certainprocedures recommended

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by the inspecting agency are carried out, the plant material is found to be free of certain diseases, the inspecting agency issues a certificate indicating that the plants are free from these specific diseases.

4. Elimination of insect vectors

5. Removal of alternative hosts. This interrupts the life cycle of some pathogens like wheat rust, Puccinia graminis which requires two hosts (wheat and barberry) to complete its life cycle.

Eradication of the pathogen1.Biological control which results in reduction of the amount of pathogen.

2. Crop rotation. For control of soilborne pathogens that infect plants one or few species. Satisfactory control through crop rotation is possible with pathogens that are soil invaders, that is, survive only on living plants or only as long as the host residues persists as a substrate for their saprophytic existence. When the pathogen is a soil inhabitant, however that is produces long lived spores or can live as a saprophyte for more than 5 to 6 years.

3. Removal and destruction of diseased plants. This can be done by burning the host plants infected by the pathogen. This prevents the spread of numerous diseases as you eliminate potential sources of inoculum.

4. Heat and chemical treatement of planting stock.

5. Soil treatments, for example with methyl bromide.

6. Sanitation.Consists of all activities aimed at eliminating or reducing the amount of inoculum present in a plant, a field or a warehouse and at preventing the spread of the pathogen to other healthy plants and plant products. Thus plowing under infected plants after harvest, such as leftover infected fruit, stems, tubers or leaves, helps cover the inoculum with soil and spread up its disintegration (rotting) and concurrent destruction of most pathogens carried in or on them.

7. Pruning infected or dead branches and removing infected fruit and any other plant debris that may harbor the pathogen.

8. Washing their hands before handling certain kinds of plants, such as tomatoes and tobacco, workers who smoke may increase the spread of TMV.

9. Disinfection of knives used to cut propagative stock.

10. Disinfecting pruning shears between trees.

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11. Washing the soil off farm equipments before moving it from one farm to another help to prevent spread.

Protection of the plantFoliage sprays or dust of planting material and/or plants in the field- protectants or

eradicantsControlling insect vectors- with spraysFertilization and manuringGood field drainage

Hosts plants resistant-cheapest, easiest, safest and most effective means for controlling plant diseases.

Control of virusesFor pathogens like viruses, there is no direct method of control using chemicals, most of the procedures are designed to prevent or restrict infection.

1. Removal and avoidance of source of infectiona. Eradication of source of infection in or near the crop.-living hosts -weeds

-volunteer plants-roguing infected plants.

-crop hygiene- treatment of implements and washing of hands eg. TMV.

b. Use of virus-free seed and planting material.-vegetative material from clean mother stock- tested and shown to be free of particular pathogen.-extraction from hydrochloric acid (HCL), or heat dried seed in HCL.-virus free plants can be obtained through tissue culture, heat therapy or chemotherapy.

c. Cultural control-planting dates escape infection at critical stage of the plant.-cultivate crops in isolated areas.-avoid overlapping susceptible crops.

2. Control or Avoidance of the vector-planting in areas free of the particular vector-avoid flights of vectors -fine mesh covers.

-chemical control of vectors.-oil sprays reduce the ability of some aphids to transmit viruses.-soilborne vectors -use of fumigants, surfactants, nematicides and fungicides.-barriers- crop barrier-bare fallow-found that 10m of bare fallow reduced the movement of leafhoppers from wild grass into maize thus reducing MSV infection.

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-biological control of vectors.

3.Protecting the plant from systemic diseases.a. cross protection

-deliberately infecting a plant with mild strain of a virus protects it against later infection by a more severe strains.

b. antiviral chemical.-used to control viral symptoms- suppress virus symptoms when applied to diseased plants without reducing virus concentration within the plant eg. benlate, bavistin, bion.

d. use of resistant cultivars.-cheapest and most effective way to combating virus diseases.

Control of bacterial Bacterial diseases are difficult to control especially with chemicals because the pathogen spends very little time on plant surfaces, multiplies quiet rapidly and no vulnerable stage that can be targeted.

1. Preventative measuresThese are aimed at pathogen avoidance, eradication and exclusion.a. Choice of site-climatic areas where disease risks are highb. strict quarantine c. eradication of any new disease that appears.d. avoid planting susceptible cultivars or alternative hosts of the pathogen.e. avoid tissue damage (especially during rain) from machinery, tools, insects.f. destroy all infected plants and plant debrisg. rotate crops, where soil infection is a problem.h. avoid water congestion.

2.Chemical controlMost successful chemicals in controlling field bacterial diseases are copper based compound.

-applied in the soil, seed, vegetative propagative material or plant foliage.a. Soil treatment.

-sterilize soil with steam or electric heat.-chemicals eg. Formaldehyde and chloropicrin.

b. seed treatment and other vegetative material.-use chemicals to disinfect the seeds-hypochlorite or HCL.-antibiotic solutions.-tool disinfection-hypochlorite, phenolic acid.

c. Foliar sprays-copper based compounds-copper sulphate, copper hydroxide.-calcium hydroxide, zeneb, zinc derivatives.-antibiotics-sprays or dips- streptomycin and oxytetracyline.

3. Biological control

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-use of bacteriocins eg. Agrocin 84 produced by Agrobacterium radiobacter effective against Agrobacterium tumefaciens. -use of saprophytic bacteria eg. Erwinia amylovora that causes fireblight in apples has been controlled by Erwinia herbicola.

4. Host plant resistance-resistance against Ralstonia solanacearum in tobacco, potato and tomatoes

Control of Fungi

a. Choice of site-climatic areas where disease risks are highb. strict quarantine c. eradication of any new disease that appears.d. avoid planting susceptible cultivars or alternative hosts of the pathogen.e. planting datef. destroy all infected plants and plant debrisg. rotate crops, where soil infection is a problem.h. avoid water congestion.

2.Chemical control

a. Soil treatment. -sterilize soil with steam or electric heat.-chemicals applied as drench on soil eg. quintozene -Rhizoctonia, Botrytis.

Zineb.b. seed treatment and other vegetative material.

-use chemicals to disinfect the seeds-captan, benlate, mancozeb.c. Foliar sprays

-maneb, bravo, antibiotics (streptomycin, cycloheximide, tetracycline)

Economic Decision Levels-keystone of insect pest management- Such levels are indispensable because they indicate course of action to be taken in any given pest situation.-bioeconomics-they have both biological and economic attributes.-sensible pesticide use is possible only with an understanding of the insect population levels that causes economic damage.-Economic decision levels in dealing with pests can increase producer profits and conserve environmental quality.-Economic decision levels are usually expressed as numbers of insects per area, plant or animal unit or sampling procedure.-Less commonly, such levels are given as degree of plant damage or combinations of numbers and damage.

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Economic Injury Level Concept (EIL)They developed the idea of economic damage, economic injury level and economic threshold collectively they called it EIL Concept.Pierce raised questions that became one incentive for developing economic injury level , ‘Is all insect attack to be computed as assessable damage? If not, at what point does it become assessable? Is control work warranted when damage is below that point? -Emerged as an encouragement for more rational use of insecticides.-emphasized the concerns of many persons regarding excessive and other inappropriate uses of insecticides.-highlighted the problem of insecticide resistance, residues and effects on nontarget organisms.-These ideas are a critical part of the concepts of integrated management replacing a simplistic strategy of ‘identify and spray’

Economic Damage and Damage Boundary

Economic damage- the amount of injury which will justify the cost of artificial control measure.Injury – is the effect of pest activities on the host physiology that is usually deleterious.[injury-pest and its activities]Damage- is a measurable loss of host utility, most often including yield quality, quantity or aesthetics.[damage –is centered on the crop and its response to injury]

As the concept applies to pest management, economic damage begins to occur when money required for suppressing insect injury is equal to the potential monetary loss from a pest population.Gain threshold has been a term used to express this beginning point of economic damage.

Gain threshold (kg/ha) = Management costs ($/ha) Market value ($/kg)

Problem: if management costs for application of an insecticide are $ 10 per hectare and harvested maize is marketed for $2 / kg. Calculate the gain threshold.

Damage boundary – the lowest level of injury where damage can be measured. The level is reached before economic damage occurs.

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Fig 2: Graph showing the relationship between the damage boundary and the Gain threshold

Economic Injury LevelThis is the lowest number of insects that will cause economic damage, or the minimum number of insects that would reduce yield equal to the gain threshold.-Even though it is expressed as number of insects per unit area, as its name implies, the EIL is really a level of injury. -Because injury is difficult to measure in a field situation, numbers of insects are used as an index of that injury.Eg. It is easier to count insect numbers than the area of foliageremovedby the pest population or the amount of juices (photosynthates) sucked from plants.-insect equivalents- instead of insect numbers in cases where several pest species causing similar injury are present these can be used. IE-is the amount of injury that could be produced by one pest through its complete life cycle. By understanding feeding activity of various species and comparing these according to the standard, EILs can be developed and decisions made for managing the whole complex.

From the previous example assuming that 1insect/plant cause 1kg/ha loss, then the EIL for the pest is 5 insects/plant. Therefore, such an insect population is considered economic, and management activities are justified. Insect populations below this level and whose potential growth will not allow them to reach this level are considered subeconomic: no management is advised.If management action (insect suppression) can be taken quickly and loss can be averted completely, then the EIL can be expressed as follows:

Vx I x P x D = C

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V-market value per unit of produce ($/kg)I-injury unit per insect per production unit (% defoliation/insect/ha)P-density or intensity of insect population (insects/ha)D-damage per unit injury (kg loss/ha/% defoliation)C-cost of management per area ($/ha)K- proportionate reduction in potential injury or damage (0.8 for 80%)

Fig.: Diagram showing relationship of the damage boundary to economic loss and the gain threshold

P = C/ [VxIxD]

EIL=P

In instances where some loss from the insect is unavoidable, for example if damage or injury can be reduced only 80%, then the relationship becomes:

EIL= C/[VxIxDxK]

Economic Threshold- probably the best known term and widely used index in making pest management decisions.-Number of insects that should trigger management action.-for this reason it is sometimes referred to as action threshold.If a pest population is growing as the season progresses, growth rates are predicted, and the ET is set below the EIL. By setting the ET at a lower value, we are predicting that once the population reaches it, chances are good that it will grow to exceed the EIL.

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Therefore it is appropriate for use to take action on an earlier date, before we accrue losses in reaching the EIL. No action is taken at levels below the ET.- The ET is based on the EIL, a value of economics and potential for injury. However, it also relies on an understanding of population dynamics because potential growth rates need to be predicted.

Fig.:Diagram showing relationship of the damage boundary to the economic injury level.

KINDS OF ECONOMIC THRESHOLDS

The ET of Stern et al. has been referred to as an operational, if not an ideal, decision rule (Mumford and Norton 1984), and it is the ultimate guideline that must be developed in any given situation. Yet, the ET is the most problematic because of considerable uncertainty.

In developing ETs, several approaches, representing different levels of sophistication, have been devised. The level of sophistication has been determined largely by existing data and needs of the particular management program. Most of these approaches can be grouped into two broad classes, subjective determinations and objective determinations.

Subjective vs. Objective ETs. Subjective determinations are the crudest approach to ET development. They are not based on a calculated EIL; rather, they are based on a practitioner's experience. These have been called nominal thresholds by Poston et al.

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(1983) and are not formulated from objective criteria. Nominal thresholds probably represent the majority of ETs found in extension publications and verbal recommendations. Although static and possibly inaccurate, these still are more progressive than using no ET at all because they require pest population assessment. Therefore, their use can often result in reduced pesticide applications.

Objective ETs, on the other hand, are based on calculated EILs, and they change with changes in the primary variables of the EILs (e.g., market values and management costs). With objective ETs, a current EIL is calculated, and estimates are made regarding potential of the pest population to exceed the EIL. The final decision on action to be taken and timing is based on expected increases in injury and logistical delays, as well as activity rates of the tactics used. Considering the various types of objective ETs, at least three can be described. These types can be termed 1) fixed ETs, 2) descriptive ETs, and 3) dichotomous ETs.

Fixed ETs. The fixed ET is the most common type of objective ET. With this type, the ET is set at a fixed percentage of the EIL, e.g., 50% or 75%. Use of the term "fixed" does not mean that these are unchanging; it means only that the percentage of the EIL is fixed. Therefore, these change constantly with changes in the EIL. The fixed ET ignores differences in population growth and injury rates; however, the percentages are usually set conservatively low; i.e., when they err, they err on the side of taking action when it is not necessary. Fixed ETs are crude, but they may be the highest level that can be developed when pest population dynamics is poorly understood. There are many examples of fixed ETs for crops, including those for pests on grapes, beans, soybean, sorghum, rice, and apples (Pedigo et al. 1986).

Descriptive ETs. Descriptive ETs are more sophisticated than fixed ETs. With descriptive ETs, a description of population growth is made, and need for, as well as timing of, action is based on expected future growth in injury rates.

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Fig: Growth of a green cloverworm, Plathypena scabra, population on soybean as indicated by incremental sampling, and projection of future growth based on a statistical model.

When larval numbers cause injury to reach the damage boundary, a statistical model based on sampling data can be applied to project future population growth. If these projections indicate that numbers will exceed the EIL during the susceptible period, then action is taken; if not, incremental sampling usually would be continued to detect any unexpected population changes until the crop is no longer susceptible. This approach has the advantage of using current sampling data to keep track of the injuriousness of the pest population. Its weakness is in making projections from earlier injury rates; i.e., future rates may not show a strong relationship to past rates, giving errors in decision making.

Dichotomous ETs. Dichotomous ETs can be developed by using a statistical procedure for classifying a pest population as economic or noneconomic from samples taken over time. The statistical procedure has been termed time sequential sampling, which can be used with the damaging stage of a pest to objectively determine its ET. The procedure is based on the sequential probability ratio test as is conventional or spatial sequential sampling. However, time sequential sampling differs in that a time perspective, rather than a space perspective, is used to make decisions. For more information on this approach see Pedigo and Buntin (1994).

ECONOMIC INJURY LEVEL CONCEPTS AND ENVIRONMENTAL QUALITY

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Previously, the use of objective ETs has had an important impact on environmental quality, particularly in certain crops where it is the basis for IPM (National Research Council 1989). Regular application of conventional ETs can result in reduced pesticide use by decreasing the frequency of application. Indeed, it has been estimated that pest monitoring, establishment of EILs, and reduced pesticide dosage can reduce pesticide use by 30 to 50%. Therefore, an expanded use of objective ETs can be considered an important tactic in conserving environmental quality However, aside from development and increased use of exiting ETs, an examination of the EIL concept itself also can lead to even further reductions in pesticide use.

Concept of Environmental EILs. The challenge of providing IPM recommendations to result in ever decreasing pesticide inputs while maintaining agricultural production and profitability is daunting. In most instances the call is made for alternative tactics that replace pesticides. Currently, particular emphasis is being placed on developing safe and profitable biological control tactics or biointensive IPM (i.e., nonchemical IPM). Important as this priority may be, there are locations, systems, and circumstances where alternative tactics are unlikely to be practical even in the distant future. Some of the situations where development of alternatives has lagged are for annual crops, sporadic pest outbreaks, and pests in northern climates, i.e., agricultural situations that comprise most of the staple commodities and their related arthropod pests.

Further decreases in pesticide inputs in these situations can and should be attempted by developing environmentally based EILs and their concomitant ETs. An Environmental EIL is an EIL that focuses on environmental issues and attempts to incorporate environmentally conscience actions in its makeup, i.e., a purposeful manipulation of the EIL variables. Activities to support greater environmental responsiveness in the EIL include accounting for environmental costs in the C variable, reducing damage per injury by increasing plant tolerance in the D variable, and developing an effective, yet environmentally responsible, K variable by reducing pesticide application rates. For detailed information on suggested manipulations of the EIL variables see Pedigo and Higley (1992).

Dynamics of Economic Injury LevelsEconomic levels are very dynamic. They vary with changes in cost, values and production environment.An insect pest feeding on the crop at one time can be expected to have a different EIL when feeding on the crop at another time the same season or in another season. These variations may be insignificant at times or vary several fold at other timesThe major forces behind change in economic decision levels are

i. crop valueii. management costsiii. degree of injury per insectiv. crop susceptibility to injury.

Crop valueIt is one of the most variable, and it alone accounts for much of the changes in EILs.

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The relationship between EIL and market value is inverse; as market value increases, EIL decreases and vice versa.

Management costThis is the cost of suppressing a pest population. As management cost increases, net benefit of control decreases. Consequently, EILs must be raised to accommodate the higher gain thresholds.MC- labour (scouting and application of insecticides), materials (insecticides), and equipment (hydraulic sprayer and sweep nets)Management costs usually change gradually, depending on the inflation rates, and therefore are usually unpredictable.

Degree of injury per insectInjury is a dual sided phenomenon, governed by insect and host populations. With the majority of insect pests, direct quantification of insect feeding has not been attempted. Most studies have emphasized yield losses, comparing these with observed insect numbers.As degree of injury per insect increases the EIL decreases.

Crop susceptibility to injuryThe relationship between injury and crop yield or utility is the most fundamental factor of the EIL. This relationship provides the biological foundation on which economic and practical constraints can be superimposed. Four major factors involved in the injury/ plant response relationship. They include i.) time of injury with relation to growth; ii). Type of injury; iii). Intensity of injury and iv). Environmental influence on the plant’s ability to withstand injury.

Calculation of Economic Decision Levels

The calculation of the EIL for an insect is a continuing process because new values are required with changes in the input variables. Consequently, when market value, management costs, and plant susceptibility change, recalculation is necessary. Additionally, several EILs are usually required for any one season because of crop development and consequent changes in susceptibility. These basic steps are required to calculate the EIL are:

1. Estimate the loss per insect2. Determine the gain threshold3. Determine the loss that can be avoided by applying the management tactic4. Calculate the EIL as:

EIL = Gain threshold ---- Loss per insect x Amount of loss avoided

Problem:

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Limitations of the EIL/ ET Concept

i. type of pest -Decision levels for management of some pest cannot be determined with EIL. Eg. many vectors, medicinal pests, veterinary pests and pathogens these often do not have a quantitative relationship between damage and injury. Since we cannot put a market value on human health and life, it is virtually impossible to put an economic limit on the control of most medicinal pests.-It is very difficult to place a monetary value on the reduction in ‘aesthetic value’ associated with a given type of pest injury. Usually any assigned value is subjective which greatly limits their usefulness in calculating EILs.-A similar problem exists with forest pests. Almost all the components of EILs are difficult to estimate for forest insects; accurate market values are a problem because projections often must be made many years in advance. Management costs may vary greatly and frequently must include more environmental and social costs than in other pest management programs. In addition the injury/ crop response relationship may be difficult to determine because the growth of the crop spans many years.

ii. management tacticSome pests have a quantitative relationship to yield, but they are still difficult to manage with EILs. Yield reduction produced but many pathogens is usually quantitatively related to pathogen number. Unfortunately sampling and quantifying the numbers or amount of these pathogens tend to be impractical. Furthermore management tactics of these pathogens are more often preventative, not therapeutic, therefore determining whether or not pathogen population is at the EIL after infection may be of significant value if the only management options available must be applied before infection.

iii. research requirement and relative unsuitability when several diverse pests (those causing different kinds of injury) occur may present serious obstacles in attempting to employ the EIL concept. However if injuries from different pests produce the same host response and can be placed on a common basis, or if effects of different injuries are additive, the concept may find application for pest complexes.

Kinds of pests and likely strategiesThe appropriate strategy and subsequent complexity of a pest management program is primarily determined by the status of a pest in the production system. Four pest types may be designed according to status. The type include noneconomic (subeconomic), occasional, perennial, and severe pests.

Subeconomic pests These insects are pests in a true sense, even if they cause insignificant losses. The GEP with this pest type is far below the economic injury level, and the highest pest

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populations fluctuations do not reach that level. Attempting to reduce injury from such pests would cost more than the losses they inflict.

Occasional pestsThis is the most common type of the pest. It has a GEP substantially below the economic injury level, but the highest fluctuations exceed this level occasionally and usually sporadically. This pest may be present on a crop most years but, does not cause economic damage.A wait and see attitude is assumed, with reliance on early detection, prediction of impending outbreaks, and employment of tactics only when the economic threshold is reached. The objective is to dampen outbreak peaks, with no efforts towards reducing the GEP.

Perennial and severe pestsThese are the most serious and difficult problem pests in crop production. Only a few insects belong in these categories, and often referred to as key pests. Problems created by these pests are usually caused by relatively high market value of the crop and/ or very dense insect populations. In this category are insects and other arthropods that attack the harvested produce directly and those that almost always occur in great numbers. Some of the worst pests may cause only blemishes on produce, making it unacceptable to consumers and resulting in serious economic losses.With perennial pests, the GEP is below but close to the economic injury level that economic injury occurs in more years than not. Only infrequently do population peaks of this pest type not reach the economic injury level.Severe pests have a GEP that is actually above the economic injury level, making them a constant problem.

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