BRE 211: Principles of Agriculture and Forestry

1
BRE 211 Principles of Agriculture and Forestry

• Lecture 4

2
Principles of Agricultural/ Crop Production

• They include
• Land preparation
• Plant propagation
• Nursery establishment
• Transplanting seedlings
• Field Planting
• Fertilizer application
• Crop protection
• Harvesting
• Post harvest handling and storage

3
Land Preparation

• Involves
• Land Clearing
• Drainage
• Preparatory cultivation
• Land Clearing
• Existing vegetation is cleared.
• Intensity of clearing varying from clear felling
  to selective thinning depending on the crops to
  be grown.
• Intensively grown crops usually require total
  clearance of the vegetation.

4
Techniques of Land Clearing

• Normally two techniques including
• Slash and Burn
• Clear Felling and Stumping
• Slash-and-burn involves
• Slashing the herbaceous undergrowth followed by
  burning of the debris and standing shrubs and
  trees.
• In some instances the bigger trees are pruned or
  ring barked and fired to kill them in places
  where they endanger the growing crops.

5
Advantages of Burning

• Releases nutrients bound in the plant tissues in
  readily soluble ash and the planted crop may
  subsist on such nutrients immediately on
  germination.
• Acts as a disinfectant that destroys pests,
  disease causing organisms and weed seeds.

6
Disadvantages of Burning

• Destroys the potential organic matter in
  vegetation by releasing the volatile nutrients
  such as nitrogen and sulphur.
• Some forest litter may resist burning thus result
  in poor land clearing.
• However,
• Burning is becoming less frequent on intensively
  farmed areas near homes and villages.
• Burning of clearings is still practiced in the
  establishment of tree crops.
• Clear felling and stumping
• This is rare but under intensive or mechanized
  cropping it is done thoroughly in order to
  facilitate mechanical cultivation.
• After clearing, soil conservation and drainage
  works commence.

7
Drainage

• Causes of Poor drainage
• Some soils have a water table permanently or
  seasonally high enough to adversely affect crop
  growth thus need drains to lower the water table.
• Physical condition of one or more horizons of the
  soil checks the downward movement of excess
  surface water thus impeding the drainage of
  excess surface water to a depth below the root
  range of crops.
• If the soil is wet and especially if it is high
  in clay content, a barrier impeding water
  percolation can also be formed by the smearing
  action of tractor wheel slip or of an implement
  which destroys structure and seals coarse pores
  and cracks.

8
Conditions for Drainage

• Where rainfall in abundant and well distributed
  throughout the year, it might be desirable to
  keep the water table below crop rooting depth at
  all times.
• Although it is necessary to improve drainage
  during part of the wet season in drier areas, it
  is undesirable to lower the water table more than
  is necessary since in such areas the objective is
  to conserve water.
• On peat soils, it is usually desirable to
  maintain the water table as high as crop
  requirements permit because draining peat too
  deeply enhances its tendency to dry, shrink and
  reach a high temperature during the day.

9
Conditions for Drainage

• Tree crops that need to develop a deep root
  system to anchor them firmly against strong winds
  will require a lower water table than some annual
  crops or surface-rooting perennials such as
  pineapple.
• Main effect of improving drainage is to improve
  the aeration of the soil enabling the crop to
  develop a deeper root system so that it can tap a
  larger volume of soil for nutrients and is better
  able to withstand periods of draught

10
Methods of improving drainage

• Sub-surface drains of tile, plastic pipe, rubble
  (bits of broken stone) and brushwood. Uncommon
  due to initial and maintenance cost
• Open surface drains Made mechanically with
  scrapers, bulldozers, and drainage ploughs or
  dragline excavators. Cheaper in cost but take up
  land, inconveniences mechanized tillage
  operations, harbour obnoxious weeds and rodents
  requiring constant maintenance.
• Ridge and furrow system Land is formed into
  broad ridges with a slight gradient on the
  furrows or ditches between them.
• Cambered bed system This is a modification of
  the ridge and furrow system in which the land is
  raised into beds.

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Drainage

• Drains cannot help once the structure of the
  surface soil has been destroyed
• They only reduce the risk of such damage
  occurring by keeping the surface layer drier and
  thus prolonging periods during which it is not
  too wet for mechanized tillage.

12
Preparatory Cultivation

• It is better to cultivate at the end of the rains
  in order to expose weed seeds, pests and
  pathogens to desiccation during the dry season.
• Extent and efficiency of preparatory cultivation
  depends on the type of soil and the cultivation
  equipment.
• Simple and light tools such as the hoe, panga,
  slasher, etc are associated with cultivation of
  soils in small-scale tropical agriculture.
• Human supplies the energy used in cultivation
  although farmers in the savanna also commonly use
  animal power.
• Tractors and their associated implements such as
  ploughs, harrows, and ridges are associated with
  highly developed agriculture of industrialized
  countries .

13
Effects of Cultivation

• Eliminates competition by weed species.
• Incorporates organic and inorganic manure.
• Improves the tilth or granular condition of the
  soil, which facilitates aeration, water
  percolation and easy rooting of seedlings.
• Helps destroy some pests and pathogens present in
  the soil by exposing them to the sun.
• Buries some weed seeds too deep for germination.
• However may turn up previously buried weed seeds
  which can dominate the re-growth after
  cultivation.

14
Plant Propagation

• Objectives
• To increase the number of plants
• To preserve the useful characteristics of the
  plants.
• Types
• Sexual Propagation (Propagation by seed)
• Asexual Propagation (by use of specialized
  vegetative parts of the plants or by artificial
  techniques such as grafting, layering, cutting or
  budding)

15
Propagation by seed

• Commonest way of propagating self-pollinated and
  many cross-pollinated crops.
• Advantages
• Seeds are usually not expensive
• Seeds can be stored for long periods
• Seeds can remain viable at least until the next
  planting season when stored in a cool dry place
• Seed does not usually carry over diseases and
  pests, which attack growing crops although some
  fungal spores infect seeds.

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Propagation by seed

• Disadvantages
• Development of off-types and variation in plant
  populations when cross-breeds are grown
• Long juvenile period when plant is unable to
  produce seeds especially in tree crops
• Some seeds do not produce plants that resemble
  their parent plants
• Some seeds cannot produce yields during the first
  year e.g. Root and tuber crops.

17
Vegetative propagation

• Depends on the ability of plant parts to
  regenerate roots and shoots and grow into new
  plants having the same characteristics as their
  parent plant.
• Advantages
• Eliminates the problems of dormancy and reduces
  the juvenile period of plants
• Yields are obtainable easier and faster than seed
  propagated plants.
• Produces seedless crops e.g. banana easily
  through
• Maintains crossbred plants in heterozygous
  condition indefinitely.
• Disadvantage
• Danger of transferring diseases to the new plants
  or locations.

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Methods of Vegetative Propagation

• Use of specialized vegetative parts or modified
  stems and roots such as bulb, corm runner,
  rhizome, suckers, tubers and root.
• Induction of adventitious roots and shoots by
  cutting or layering the stem e.g. in tea and
  sweet potato propagation.
• Grafting Two plant parts are joined by
  regeneration of their tissues.
• Budding Only the vegetative bud is joined to
  another plant where it regenerates a new plant.
• Ratooning Outgrowths from stools of a harvested
  crop are used.

19
Nursery Establishment

• A Nursery phase is an important part of the
  planting operation for most trees and some field
  crops.
• Seedlings can be better cared for and
  conveniently watered with less effort to increase
  growth and development.
• Characteristics of a good nursery site
• Should be near a source of water
• Should be as near as possible to the site of
  field planting
• Site should not be subject to planting other
  crops.
• Ground should be level or terraced.

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Nursery Requirements

• Water
• A small nursery can be watered using watering
  cans by family labour while a larger one may
  require more workers or the use of a pump and
  hose system.
• Polythene bags
• Most widely used containers for nursery seedlings
  because they are cheap and durable and make
  handling of seedlings at planting very easy.
• size of bags used depends on the seedlings.
• Shade
• Young seedlings do better under partial shade at
  the early stages. they will become self-shading
  when they get larger

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Nursery Requirements

• Fertilizer
• Usually nursery seedlings will grow faster if
  fertilized. The easiest way to fertilize
  seedlings is to dissolve a nitrogen fertilizer
  containing all the major nutrients in water and
  water lightly once every week.
• Fertilizer scorch can be avoided by immediately
  re-wetting with water alone.
• Sometimes micronutrient deficiencies will occur
  and these are best dealt with by watering with a
  complete/compound fertilizer dissolved in water
  and given periodically.

22
Transplanting seedlings

• Should be done during a sufficiently wet season.
• Before planting the seedlings, any weak,
  slow-growing, diseased, deformed or otherwise
  abnormal plants should be discarded as it affects
  the long-term yield of the field planting.
• Seedlings grown in Polythene bags are easy to
  transport to the field and lorry, tractor,
  trailer or hand may carry them depending on the
  situation.

23
Transplanting seedlings

• Use a box and double poles carried on the
  shoulders of two workers to carry seedlings over
  rough ground.
• Before planting the Polythene bags must be
  stripped off by slitting lengthwise with a razor
  blade or a very sharp knife.
• Although Polythene bags are widely used for
  nurseries some farmers may still prefer to plant
  seedlings directly in the soil.
• This often means that considerable damage is done
  to the seedling on extraction, thus delaying its
  development.

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Field Planting

• Seed or planting material largely determines the
  quantity and quality of the harvested produce.
• Good stocks of planting materials ensure
• Reduced costs of cleaning, standardization and
  disinfection
• Uniform germination thus eliminating replanting
  or supplying missing stands
• Vigorous seedling growth which reduces weed and
  disease damage
• Uniform growth rates, maturity and produce

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Field Planting

• Low grade or poor-quality planting materials lead
  to
• Uneven germination and establishment which may
  necessitate replanting or supplying missing
  stands
• Feeble seedling growth susceptible to disease and
  insect damage
• Costly disinfection or grading of planting
  materials against seed-borne diseases and pests
• Uneven growth rates due to lack of uniformity in
  genetic composition.
• Uneven maturity which affects the cost and
  efficiency of harvesting
• Lack of uniform produce due to a combination of
  all the above factors.

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Field Planting

• This affects not only the efficiency of primary
  processing but also the quality and market value
  of the products.
• Most farmers in the tropics still provide for
  their planting materials from their own harvests
  or purchase them from unregulated markets.

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Methods of planting

• Broadcast
• This is limited to crops that will be
  transplanted particularly small seed crops. It is
  unsuitable for large seeds and vegetative
  cuttings
• Drilling
• This is planting seed in small furrows
• Dibbling
• Holes are made and the seeds placed in these
  holes and covered. The crops could be planted in
  scattered like beans.

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Sowing Practices

• The successful establishment of seedlings of
  annual crops depends upon
• Viable seed of adapted cultivar
• Uniform sowing placement depth
• Firm seed-soil contact
• Availability of moisture and nutrients in the
  soil
• The factors involved in sowing management can be
  divided into two broad groups
• Mechanical factors such as depth of planting,
  emergence habit, seed size, seedbed texture, and
  seed-soil contact.
• Biological factors such as companion crops (in
  mixed cropping and pastures) and competition for
  light.

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Spacing and plant population

• Spacing crops optimally reduces interplant
  competition for sunlight, moisture, air and
  nutrients.
• The ultimate yield from a unit land area is
  contributed to by all the plants growing on it.
• Excessively wide or narrow spacing leads to
  reduction in yield.
• The exact spacing for any crop depends on
• Soil productivity
• Location
• Time of planting.
• On fertile moist soils, closer spacing will give
  better results than on poor soils or soils
  susceptible to moisture stress.
• This explains the sustained high yields from
  close spacing and high plant populations in
  irrigated as compared to rainfed crops.

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Fertilizer Application

• Fertilizers are chemical compounds containing the
  elements that are added to the soil to supplement
  its natural fertility.
• Fertilizers containing only one of the major
  elements (N, P, and K) are single, simple or
  straight fertilizers
• Those containing two or three elements are
  classified as mixed compound or complex
  fertilizers.

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Fertilizer Application

• Nutrients in fertilizers must come within the
  feeding range of plants roots for maximum
  benefit from the application.
• The soluble constituents of fertilizers diffuse
  through the soil vertically and only slightly in
  a lateral direction.
• The method of application therefore must ensure
  distribution in a moist soil to reach the plant
  roots.
• Thus method of applying fertilizer is important.

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Methods of Fertilizer Application

• Broadcast before planting Fertilizer is spread
  as uniformly as possible over the field after
  ploughing land then mix it with soil by ploughs
  or cultivators.
• Gives good results with crops like millet which
  are planted in narrow rows.
• Suitable for those crops whose seeds are usually
  broadcast.
• However, it stimulates weeds.
• Row Placement Fertilizer is placed in bands or
  in localized areas along rows at a calculated
  distance for maximum absorption by the plants.
• Advantages
• Fertilizer comes in contact with minimum amounts
  of soil particles reducing phosphorus fixation.
• Fertilizer is within reach of the roots and the
  plant can feed on it easily
• Fertilizer placed in bands does not supply
  nutrients to the weeds near the surface

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Methods of Fertilizer Application

• Top-dressing Second application by broadcasting
  on the soil surface close to the plants when the
  crop is 3-4 weeks old.
• Drill placement Fertilizer is applied along
  with the seed.
• Good for crops like wheat, maize and other
  cereals, which can withstand contact with the
  fertilizer.
• Band Placement Fertilizer is placed in bands on
  one side or both sides of the row about 5cm below
  the seed and 4cm away from the seed or plant.
• The method is useful for cotton, tomato and
  potato crops that are sensitive to direct contact
  with fertilizer.
• Side-dressing Second application when the crop
  is partly grown (4-8 weeks) given as a continuous
  band near the crop row to a depth of 4-5 cm.

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Methods of Fertilizer Application

• Application by plough Fertilizer is placed in a
  continuous band at the bottom of the plough
  furrow. Each band is covered as the succeeding
  furrows are turned over.
• Applying liquid fertilizer Fertilizer is mixed
  with most fungicides and pesticides and applied
  simultaneously or dissolved in irrigation water
  and applied together in a process referred to as
  fatigation
• Used for high-value crops by direct spraying.
• Carbamide (urea) is the most commonly used in
  this way.

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Types of Fertilizers

• Nitrogenous fertilizers
• Phosphatic fertilizers
• Potassium fertilizers
• Mixed or compound fertilizers.
• Farmyard manure

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Nitrogenous Fertilizers

• All major inorganic fertilizers in common use are
  synthetically produced.
• Many nitrogenous compounds are made from ammonia
  in an atmospheric nitrogen manufacturing process
  known as the harber process.
• Hydrogen is combined with nitrogen in the ratio
  31 by volume at high temperature (400-500 o C)
  and pressure (200-1000 atmosphere) in the
  presence of catalyst form ammonia.
• This ammonia is used directly as fertilizers or
  is converted into various nitrogen fertilizers.

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Phosphatic fertilizers

• Are of three grades depending on their
  solubility.
• Water-soluble phosphate
• Citrate-soluble phosphate
• Phosphates that are only soluble in strong
  mineral acids such as sulphuric acid and nitric
  acid.
• The solubility depends on the chemical
  composition or formula of the phosphate and the
  degree of fineness.

38
Potassium Fertilizers

• Manufactured from natural deposits of potassium
  salts found in various parts of the world.
• The crude potash minerals are dissolved in water
  and the various salts separated by fractional
  distillation.
• All are soluble in water and the potassium
  content is readily available to plants unlike the
  nitrogen fertilizers.
• Most potash fertilizers have no effect on soil
  pH.
• Most important potash fertilizer materials are
• Muriate of potash
• Sulphate of potash

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Mixed or compound fertilizers

• Contain at least two of the three major elements
  N, P, K.
• Advantages of compound fertilizers include
• Can be applied by hand as well as a fertilizer
  drill since it is usually dry with fine and
  well-mixed granules.
• Is stable and does not cake up, form lumps or
  deteriorate in any way over time.
• Contains all the major plant nutrients in the
  right proportions.
• The ready-made mixture saves farmers the labour
  of mixing fertilizers.
• Save time and labour when applied in the
  calculated amount instead of using separate
  straight fertilizers.
• Disadvantages include
• Cost slightly more than the total cost of three
  equivalents of NPK.
• May be unsuitable for many soils.

40
Farmyard Manure (FYM)

• FYM refers to all the refuse from farm animals.
• It is a by-product consisting of two components
  solid and liquid in a ratio of 31.
• Solid part is made up of dung and straw that has
  been used for animal bedding while the liquid
  comes from the urine.
• Dung comes mostly from undigested material and
  the urine from the digested material that is
  absorbed by the animal and then excreted.
• More than 50 of the organic matter contained in
  dung is in the form lignin and protein similar to
  those contained in humus.
• This material is quite resistant to further decay
  and therefore the nutrients present in this
  fraction of dung are liberated very slowly.
• Nutrients present in the urine are readily
  available either directly or after simple
  decomposition.
• Over half of nitrogen, almost all the phosphate
  and about two fifths of potash are found in the
  solid portion.

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Farmyard Manure (FYM)

• Manure is essentially a nitrogen-potash
  fertilizer.
• Manure supplies nutrients required by plants.
• Because it originated from plants, FYM naturally
  contains all mineral constituents including trace
  elements.
• FYM improves the physical properties of the soil
  by increasing humus content and consequently the
  water holding capacity of the soil.
• Carbonic acid helps to release minerals present
  in FYM.
• It releases these nutrients fastest when the soil
  provides warm moist conditions favourable for
  microbial decomposition.

42
Factors affecting Fertilizer Use

• Crop factors
• Certain crops need larger amounts of particular
  nutrients than others e.g. Legumes require large
  amounts of P whereas grains require
  proportionately more N.
• Crop variety Recently developed varieties are
  more responsive to higher doses of fertilizer
  than traditional crop varieties.
• Soil Factor
• Soils differ in their potential for production.
• Large applications of fertilizer can be
  profitable on soils that have high potential but
  are low in fertility
• Climatic factor
• Soils in areas of low rainfall lose little by
  leaching thus nutrients level remains stable. If
  fertilizers are added, the limited amount of
  water available means that the plants are unable
  to respond.
• Soils of humid regions lose nutrients through
  leaching and weathering but their water supply is
  adequate for high crop production. Here,
  fertilizer application will show good results.

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Factors affecting Fertilizer Use

• Economic factor
• Fertilizer use is increase by low prices and
  decreased by high prices.
• Crop prices have the opposite effect High price
  for the crop will give a profitable return from
  large fertilizer application yield but follow a
  curve of diminishing returns
• Management factor
• Managers choose the input-output levels at which
  they will operate. Increased crop outputs usually
  require increased fertilizer inputs.
• Top yields depend on many factors including soil
  type, climate, cropping history, fertilizer
  history and soil amendments, tillage practices,
  weed control and timing of operations. Most of
  these are managerial factors.

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Effects of Fertilizer Application on Agriculture

• Use of mineral fertilizers boosts crop growth
  which harvested provides a considerable amount of
  residue adding the organic content of the soil.
• When well fertilized, cereals e.g. millet, maize
  and sorghum leave behind considerable organic
  residue in the form of roots, stumps and stalks
• When nitrogen is applied or a cereal-legume
  rotation is adopted, the organic residue
  undergoes rapid microbial decay to produce humus.
• Thus the use of fertilizers in conjunction with
  farmyard manure increases the efficiency of crop
  plants.

45
Crop Protection

• Crops are protected against
• Fire
• Pests
• Diseases
• Weeds
• Pests and diseases are among the most serious
  limiting factors to economically efficient crop
  production and utilization of natural resources
  in tropical agriculture.
• Crop losses through pests and diseases may
  sometimes be negligible but at other times total
  loss especially as a result of sporadic outbreaks
  of non-economic pests and diseases.
• Pests and disease-causing organisms or pathogens
  include rodents, bats, birds, insects, mites,
  molluscs, nematodes, weeds, parasitic plants,
  fungi bacteria, mycoplasma, viruses and sometimes
  humans.
• Some diseases are, however, caused by physical or
  soil factors.

46
Crop Pests

• Arise in two major ways.
• Natural occurrence Sudden attack of crops by
  insect e.g. locust outbreaks in arid and
  semiarid regions.
• Alteration of the ecosystem People attempting to
  change the ecosystems for their own benefit
  creating conditions that favour the development
  of pests. Some of these human activities

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Classification of Pests

• According to damage they cause
• Biting and chewing insects
• Piercing and Sucking insects
• Boring insects

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Classification of Pests

• According to Severity of damage c
• Key or major pests cause serious and persistent
  economic damage in an ecosystem in the absence of
  effective control measures.
• Minor pests Cause economic damage only under
  special circumstances in their local environment.

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Classification of Pests

• Numbers of organisms involved
• Frequency of occurrence
• Occasional pests
• Potential pests
• Migrant pests

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Fundamental Principles of Crop Protection

• Control of pests and plant diseases means the
  reduction in the amount of damage caused.
• Perfect control is rare, but there is economic
  control when the increase in yield more than
  covers the cost of chemicals, materials and
  labour used for the control operations.
• The fundamental principles of control include.
• Exclusion
• Preventing entrance and establishment of pests in
  farms, states or countries.
• Involves using certified seeds or plants,
  discarding any that are doubtful, possibly
  treating seeds or tubers before they are planted.
• For states and countries, exclusion also includes
  quarantine prohibition by law.

51
Fundamental Principles of Crop Protection

• Eradication
• Eliminating pest once already established on a
  plant or in a farm through.
• Removal of the diseased specimens or cutting off
  cankered tree branches eradication could be aided
  by control viral diseases
• Cultivation and deep ploughing to bury plant
  debris
• Rotation of susceptible with non-susceptible
  crops in an attempt to starve out the pest
• Disinfection with chemicals
• Heat treatment
• Spraying or dusting foliage with pesticides
• Treating soil with appropriate chemicals to kill
  insects, nematodes and fungi
• Trapping rodents

52
Fundamental Principles of Crop Protection

• Protection
• Placing a protective barrier between the
  susceptible part of the host and the pest.
• In most instances this is a protective spray or
  dust applied to the plant in advance of the
  arrival of the pest.
• Sometimes it means killing insects or other
  inoculating agents,
• Storage of food surpluses, preservation by
  freezing, canning, salting etc. can also protect
  the food items from pest damage.

53
Fundamental Principles of Crop Protection

• Immunization
• Control by the development of resistant varieties
  or by inoculating the plant with something which
  will inactivate the pest or pathogen.
• Avoidance
• Growing crops during period when the pest
  population is low or absent in the field.
• Crop is planted to avoid the damaging pest
  population.
• The use of early and rapidly maturing varieties
  can also have profound effect on the degree of
  pest damage experienced by the crop
• Insects and other arthropods are the most serious
  pests of crop plants in tropical agriculture.

54
Pest Control

• Objective
• To reduce the population of the offending pests
  below the economic threshold when its damage
  becomes uneconomical i.e. does not cause losses
  in yield.
• A pest control method will therefore be
  considered successful if it can maintain the pest
  population well below the economic threshold.
• Complete eradication of a pest from an ecosystem
  is not readily practicable or even desirable.
• Basic principles of pest control include
• Preventing pests from gaining access to the host/
  Pest-host interaction prevention.
• Killing the pest directly reduces the population
  of the pest on the host.

55
Methods of Pest control

• Include
• Physical control
• Legislative control
• Cultural control
• Biological control
• Chemical control
• Integrated pest management (IPM)

56
Physical control

• Includes the use of various barriers to prevent
  pests from physical contact with their hosts and
  mechanical removal or destruction of the pest.
• Barriers may be mechanical, chemical or
  behavioral.
• Mechanical barriers include
• Wire fences
• Mosquito nets
• Fine nylon net sleeves
• Nylon or paper bags
• Sticky bands
• Boots for waders
• Concrete foundation - prevent termites.
• Hand picking
• Flooding
• Lethal temperatures
• Hermetic storage Tightly closed bins
• Radiation

57
Physical control

• Chemical barriers include
• Prophylactic chemical treatment carried out on
  crops leaving a residual poison that is lethal to
  the pest.
• Behavioral barriers exploit the fact that pests
  locate their hosts by responding to external
  stimuli such as sight and oduors.
• They include
• Frightening devices.
• Traps
• Attractants
• Anti-feedants inhibit feeding of pests

58
Legislative Control

• Is the use of laws and regulation to prevent the
  importation of pest organisms into a country and
  to restrict the spread of pests from areas where
  they are already established.
• Main objective is to prevent dangerous pests from
  colonizing new areas.
• Include
• Quarantine Restricts movement of produce from
  areas of infection to other areas
• Eradication regulations
• Certification regulation

59
Cultural Control

• Is the manipulation of regular agronomic
  practices to influence on the incidence and
  populations of crop pests.
• The basic principle of cultural control is the
  disruption of the development and life cycles of
  pests either by denying them their food or by
  exposing stages in then life cycle to adverse
  conditions so that they are killed.
• Advantages
• Relatively cheap and effective.
• Poses minimal danger to the environment.
• Cultural control involves
• Cultivation of the soil
• Variation in planting and harvesting dates
• Crop rotation
• Close season
• Trap cropping
• Resistant crop varieties
• Mixed cropping
• Good husbandry practices

60
Biological Control

• Is deliberate use of organisms (parasites,
  predators and pathogens) to reduce populations of
  pests.
• Such natural enemies may be arthropods (insects
  and mites), bacterial protozoan, fungi, viruses,
  nematodes or even vertebrates (birds, toads,
  fish).
• Method is usually used as a supplement to other
  methods of control.
• Successful biological control requires that
• Pest population is reduced to levels well below
  the economic threshold.
• Population is maintained sufficiently low to
  allow the survival of the biological control
  agent.

61
Biological Control

• Biological control requires thorough knowledge of
  the ecosystem, the ecology and behaviour of the
  target pest and the bio-control agent.
• Advantages
• It is safe and cost-effective
• Is devoid of environmental pollution problems
  associated with chemical control.
• Care must be exercised, however, not to upset the
  ecosystem of the area by the manipulation of
  controlling species.

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Chemical control

• Most common and easily applicable method for
  reducing or preventing economic pest damage is
  the use of toxic substances or pesticides to kill
  or repel pests on their host crops.
• Continues to play a significant role in solving
  the food and wealth problems of tropical
  countries.
• Advantages
• Relatively easy method of pest control
• Produces quick and easy results
• Can be repeated as often as desirable
• Is cheap and individual farmers can take
  independent action on their own farms
• The broad-spectrum action of many pesticides
  makes it possible to control a complex of pests
  with one or a combination of pesticides.

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Chemical control

• Disadvantages
• Is repetitive and must be applied whenever there
  is a pest outbreak. Thus it is wasteful
• Pesticide applied rarely kills all the pests and
  the residual population which survives soon
  develops to cause economic damage
• Pesticides can be toxic to beneficial insects
  especially parasites, predators and pollinators.
  They are potentially toxic to wildlife, fish and
  humans
• Cause environmental pollution and ecological
  disturbance. Toxic residues may remain in
  agricultural produce.
• Pests may develop resistance to a pesticide which
  reduces the effect of that pesticide on that pest
• Chemical control provides only a temporary
  solution to pest problems
• Pesticides are expensive to manufacture and
  usually have to be imported by tropical
  countries.