Transcript Environmental Impact Assessment (EIA)

BRE 211: Principles of
Agriculture and Forestry
Lecture 4
Principles of Agricultural/
Crop Production
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They include:
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Land preparation
Plant propagation
Nursery establishment
Transplanting seedlings
Field Planting
Fertilizer application
Crop protection
Harvesting
Post harvest handling and storage
Land Preparation
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Involves:
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Land Clearing
Drainage
Preparatory cultivation
Land Clearing
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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.
Techniques of Land Clearing
 Normally
two techniques including:
 Slash
and Burn
 Clear Felling and Stumping
 Slash-and-burn
 Slashing
involves:
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.
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.
Disadvantages of Burning
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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.
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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.
Drainage
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Causes of Poor drainage:
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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.
Conditions for Drainage
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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.
Conditions for Drainage
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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
Methods of improving drainage
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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.
Drainage
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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.
Preparatory Cultivation
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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.
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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 .
Effects of Cultivation
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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.
Plant Propagation
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Objectives:
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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)
Propagation by seed
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Commonest way of propagating selfpollinated and many cross-pollinated crops.
 Advantages:
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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.
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.
Vegetative propagation
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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:
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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:
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Danger of transferring diseases to the new plants or
locations.
Methods of Vegetative
Propagation
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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.
Nursery Establishment
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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
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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.
Nursery Requirements
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Water:
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Polythene bags:
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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.
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:
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Young seedlings do better under partial shade at
the early stages. they will become self-shading
when they get larger
Nursery Requirements
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Fertilizer:
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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.
Transplanting seedlings
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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.
Transplanting seedlings
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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.
Field Planting
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Seed or planting material largely determines
the quantity and quality of the harvested
produce.
 Good stocks of planting materials ensure
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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
Field Planting
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Low grade or poor-quality planting materials
lead to:
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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.
Field Planting
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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.
Methods of planting
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Broadcast:
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Drilling:
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This is limited to crops that will be transplanted
particularly small seed crops. It is unsuitable for
large seeds and vegetative cuttings
This is planting seed in small furrows
Dibbling:
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Holes are made and the seeds placed in these
holes and covered. The crops could be planted in
scattered like beans.
Sowing Practices
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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.
Spacing and plant population
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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:
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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.
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.
Fertilizer Application
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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.
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.
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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
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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
Methods of Fertilizer Application
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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.
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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.
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Good for crops like wheat, maize and other cereals, which
can withstand contact with the fertilizer.
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.
Methods of Fertilizer Application
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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
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Used for high-value crops by direct spraying.
Carbamide (urea) is the most commonly used in
this way.
Types of Fertilizers
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Nitrogenous fertilizers
Phosphatic fertilizers
Potassium fertilizers
Mixed or compound fertilizers.
Farmyard manure
Nitrogenous Fertilizers
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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.
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Hydrogen is combined with nitrogen in the ratio
3:1 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.
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.
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solubility depends on the chemical
composition or formula of the phosphate
and the degree of fineness.
Potassium Fertilizers
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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:
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Muriate of potash
Sulphate of potash
Mixed or compound fertilizers
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Contain at least two of the three major elements N, P,
K.
 Advantages of compound fertilizers include:
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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.
Farmyard Manure (FYM)
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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 3:1.
 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.
Farmyard Manure (FYM)
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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.
Factors affecting Fertilizer Use
Crop factors
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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
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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
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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.
Factors affecting Fertilizer Use
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Economic factor
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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
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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.
Effects of Fertilizer Application on
Agriculture
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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.
Crop Protection
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Crops are protected against:
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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 noneconomic 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.
Crop Pests
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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
Classification of Pests
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According to damage they
cause
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Biting and chewing insects
Piercing and Sucking insects
Boring insects
Classification of Pests
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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.
Classification of Pests
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Numbers of organisms involved
Frequency of occurrence
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Occasional pests
Potential pests
Migrant pests
Fundamental Principles of
Crop Protection
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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
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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.
Fundamental Principles of
Crop Protection
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Eradication
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Eliminating pest once already established on a
plant or in a farm through.
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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
Fundamental Principles of
Crop Protection
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Protection
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Placing a protective barrier between the
susceptible part of the host and the pest.
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In most instances this is a protective spray or
dust applied to the plant in advance of the arrival
of the pest.
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Sometimes it means killing insects or other
inoculating agents,
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Storage of food surpluses, preservation by
freezing, canning, salting etc. can also protect
the food items from pest damage.
Fundamental Principles of Crop
Protection
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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.
Pest Control
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Objective
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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
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Preventing pests from gaining access to the host/ Pesthost interaction prevention.
Killing the pest directly reduces the population of the
pest on the host.
Methods of Pest control
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Include:
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Physical control
Legislative control
Cultural control
Biological control
Chemical control
Integrated pest management (IPM)
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:
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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
Physical control
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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
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Frightening devices.
Traps
Attractants
Anti-feedants – inhibit feeding of pests
Legislative Control
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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:
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Quarantine: Restricts movement of produce
from areas of infection to other areas
Eradication regulations
Certification regulation
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:
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Relatively cheap and effective.
Poses minimal danger to the environment.
Cultural control involves:
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Cultivation of the soil
Variation in planting and harvesting dates
Crop rotation
Close season
Trap cropping
Resistant crop varieties
Mixed cropping
Good husbandry practices
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:
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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.
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.
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:
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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.
Chemical control
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Disadvantages
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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.