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Pesticide Application
Introduction
Regardless of the potential efficacy of a pesticide against a target pest, its efficacy in the field or on the
target will depend on the application technique used
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It is important that the quantity of pesticide needed to do
the job is applied to the target area with a uniform distribution
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Improper application techniques can result in too little or too much pesticide reaching the
target, resulting in inadequate control in the former case and waste, phytotoxicity, pest resistance,
environmental contamination and human health risks in the latter
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The application equipment chosen for a particular job should be
influenced by the type of formulation, working conditions, the type of area or crop to be treated and
specific problems in the area
...

Different types of application equipment available are: Hydraulic sprayers*; Air blast sprayers*; Low
pressure boom sprayers*; High pressure boom sprayers; ULV (ultra low volume) sprayers; Granule and
bait applicators; Thermal foggers; Cold foggers; Fumigation applicators; Aerosol generators; Hand
dusters; Power dusters; Fixed wing aircraft; Helicopters; Applicators for livestock
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Hydraulic sprayers
Compressed air sprayers
These are usually hand carried sprayers which operate under pressure
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The tank containing the pesticide is pressurized by means of a self contained manual pump
before spraying commences
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Nozzles are interchangeable
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2

Lever operated knapsack sprayers
Lever operated knapsack sprayers are designed to fit comfortably on the operator's back
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The piston pump is preferred
when high pressures are required while the diaphragm is preferred where suspensions are being
applied
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Advantages: Easy to use and inexpensive; Suited for small space jobs; Easy to clean and simple to repair
Disadvantages: Operator fatigue results in variations in pressure hence variations in droplet size;
Pesticides corrode steel parts and breakdown rubber; Poor cleaning results in rapid deterioration of
equipment; Rapid fall in pressure results in changes in droplet size
Air blast sprayers
These sprayers use a high speed, fan driven air stream to break up nozzle output into fine droplets
which move with a blast of air to the target
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Advantages: Give good coverage and penetration; they operate at low pressures; Have mechanical
agitation
Disadvantages: Hard to confine spray to target area: Some large and cannot be used in small areas
Mistblowers: Mistblowers are knapsack air blast sprayers designed to apply low volumes of highly
concentrated sprays
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Flow
of liquid into the airstream is controlled by a restrictor
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The pump should have a pumping capacity
of sufficient volume, to supply the system and maintain desired pressure when operating at full
capacity
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NOZZLES
The function of the nozzle is to break the spray into droplets and control the final dispersal of the spray
through short distances
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Nozzles are usually classified
according to the type of energy used to break the spray into droplets e
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hydraulic and gaseous
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Hydraulic nozzles: produce droplets when liquid under pressure is forced through a small orifice with
sufficient velocity energy to break the liquid into droplets
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The nozzle body holds the strainer and tip in position, while the cap secures them to the body
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They 3

control the flow rate and may be interchanged on single nozzle body to provide a variety of spray
patterns
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Impact or flooding nozzles: produce a fan shaped spray pattern when a jet of fluid passes through a
relatively large orifice and impinges at high velocity on a smooth surface at a high angle of incidence
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Fan nozzles: produce a fan shaped spray pattern when two jets of liquid strike each other at an angle
greater than 90o
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The
regular flat fan produces an oval pattern with tapered ends
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The even flat fan produces a narrow oval spray, uniform across its
width
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Cone nozzles: produce a cone shaped spray pattern
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These nozzles may produce a solid or hollow cone pattern and are used where penetration and
coverage of plant foliage and other irregular targets are desired
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Solid stream nozzles: are similar to cone nozzles but without a swirl chamber
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Gaseous energy nozzles: Gaseous energy nozzles produce droplets when a liquid impacts with a high
velocity air stream
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The most important variable for droplet
size control is the air/liquid ratio
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Droplet Size and Distribution
Sprays emitted from nozzles contain a large number of small spheres called droplets
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Pesticide sprays are classified according to droplet size
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4

Aerosols are usually used in pesticides for flying insects
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g
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A fine spray is used
when a compromise between reduced drift and good coverage is required
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Mixing and Diluting
The method for measuring and mixing will vary depending on the formulation being used
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Formulations which mix easily with water can be measured and poured directly
into the mixing container about 3/4 full of water
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Wettable powders should be premixed into a paste before adding to mixing container as above
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Ungraduated equipment (e
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Some wettable powder formulations provide scoops for measuring
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Rate calculations (dilutions)
Powders
Recommended dosages for powder formulations may be given in kg per 100 litres or per hectares
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) = kg needed
100 litres
If recommendation is in kg/ha
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Litres preparation = hectare preparation will spray
Litres applied per/ha
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)

Hectares to be sprayed x kg formulation/ha = kg needed
If recommendation is in g a
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/ha
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i
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to g formulation/ha
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i
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i
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If recommendation is in litres/100 L
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(rec
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Litres preparation = hectares preparation will spray
Litres applied per/hectare (rec
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i
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:Convert litres a
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/hectare to litres formulation/hectare
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i
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i
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Calibration of hand operated knapsack sprayers
To determine the quantity of chemical needed per unit area (litres/hectare), the following needs to be
determined:1
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The swath width in metres
3
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However, the
discovery of synthetic organic pesticides led to the extensive use of pesticides to control pests during 6

the 1940s and 1950s
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In fact, the agricultural sector became even more heavily dependent on pesticides, which
were seen as the remedy for all pest problems and led to pesticides being used injudiciously
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The three “R”s - pest resistance, resurgence, and
replacement - are the major sources of ecological backlashes and from these stem other backlashes
(Pedigo, 1991)
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When a pesticide is applied
on a pest population, a certain percentage (normally a small minority) of physiologically stronger
individuals always survive
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Each time the
pesticide is applied, the resistant individuals will survive and reproduce while the weaker, susceptible
ones will be killed
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PEST RESURGENCE - The use of synthetic pesticides over an extended period of time may keep the
target pest population in check at first but eventually, the pest population will recover and occur in even
higher numbers than that which was present to begin with
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Destruction of the key pest’s natural enemies - this may be through direct contact with the pesticide,
feeding on poisoned host/s and starvation because of the absence of the host (pest)
2
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Favourable effect on the pest’s physiology and behaviour - for instance, sub-lethal concentrations of
insecticides may stimulate egg production in insects
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REPLACEMENT BY SECONDARY PESTS - Cultivated crops and livestock usually have a complex of pests
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Hence, the most
destructive pest is the major (or key) pest; the other secondary pests cause only minor damage of little
economic importance because their populations are kept at low levels by their natural enemies
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Other backlashes are destruction of microbes, enhancement of microbial action, and the creation of an
ecological imbalance
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This will influence the persistence of
the insecticide in the environment and the impact on non-target organisms
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The
fate of a pesticide in the soil depends upon its physical removal and degradation, which involve erosion
or run-off, leaching, volatilisation, biological removal, and microbial, chemical or photochemical
degradation
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