Unit 5: Plant Protection Equipment

I. Orientation: Principles of Plant Protection Equipment

Plant protection equipment applies pesticides, biological agents, or other crop-protection materials uniformly and safely to plants, soil, or stored produce. Sprayers deliver chemicals as liquid droplets, while dusters deliver finely divided solid particles. Their effectiveness depends on correct dose, suitable droplet or dust size, uniform coverage, proper timing, and safe operation.

• Purpose: Control insects, diseases, weeds, and other pests while minimizing damage to crops, operators, and the environment.
• Application forms: Sprayers use liquid formulations such as solutions, emulsions, or suspensions; dusters use dry powders.
• Uniformity: Every treated area should receive approximately the recommended quantity; excessive application causes residues and crop injury.
• Calibration: Application rate is commonly expressed as litres per hectare (L/ha) for sprays or kilograms per hectare (kg/ha) for dusts.
• Coverage: Sprays require suitable droplet size and nozzle distribution; dusts require fine particles and air movement for spreading.
• Operating conditions: Wind, temperature, humidity, crop stage, and pest location influence application efficiency and drift.
• Safety principle: Operators must use protective clothing, avoid leaks and inhalation, and clean equipment without contaminating water sources.

II. Sprayers — Liquid Application Equipment

A. Components

A sprayer is a machine that takes a pesticide mixture from a tank, pressurizes it, and discharges it through nozzles as controlled droplets.

• Tank: Holds the spray mixture, commonly made of polyethylene, fiberglass, or corrosion-resistant metal.
  • Capacity: Small knapsack sprayers may hold 10–20 L; tractor-mounted tanks may hold several hundred litres.
  • Filling opening: A screened opening prevents leaves, stones, and undissolved material from entering.
• Agitator: Keeps wettable powders and suspension concentrates evenly mixed so that heavier particles do not settle at the tank bottom.
• Pump: Produces the pressure needed to move liquid through the delivery system.
  • Piston or diaphragm pumps: Used where relatively high pressure and resistance to chemicals are required.
  • Centrifugal pumps: Suitable for high-volume, lower-pressure applications.
• Pressure regulator: Maintains selected operating pressure and returns excess liquid to the tank through a bypass line.
• Pressure gauge: Shows liquid pressure, usually in kilopascals (kPa), bar, or pounds per square inch (psi).
• Filters and strainers: Remove particles before the pump and nozzle; a blocked nozzle often indicates inadequate filtration.
• Hoses and pipes: Carry liquid from the tank to the boom, spray gun, or lance and must withstand the working pressure.
• Boom: Supports several nozzles at a fixed spacing for field crops; its height strongly affects spray overlap.
• Nozzles: Convert pressurized liquid into droplets and determine flow rate, spray pattern, and droplet size.
  • Flat-fan nozzles: Produce overlapping fan patterns for boom spraying.
  • Hollow-cone nozzles: Produce fine droplets and are often used for insecticide or fungicide coverage.
  • Solid-cone nozzles: Deliver a denser central spray for some specialized applications.
• Frame and controls: Support the tank and pump and provide levers, valves, throttle controls, and pressure adjustment.

B. Working

The working principle of a sprayer is hydraulic atomization: pressure forces liquid through a small nozzle opening, breaking it into droplets that cover the target surface.

• Mixing: The pesticide is measured and mixed with the recommended quantity of water in the tank; wettable powders should first be made into a slurry.
• Pressurization: The pump draws liquid through the suction filter and delivers it under pressure to the discharge line.
• Regulation: The pressure regulator controls the pressure while surplus liquid may return to the tank, maintaining agitation.
• Atomization: At the nozzle, pressure energy becomes liquid velocity; the nozzle orifice and internal design determine spray pattern and droplet size.
• Application: The operator maintains a steady travel speed, boom height, and pressure so that each nozzle applies a consistent rate.
• Calibration relationship: For a boom sprayer, application rate can be estimated by:

Application rate (L/ha) =
600 × nozzle flow (L/min)
--------------------------------
nozzle spacing (cm) × speed (km/h)

• 600: Unit-conversion constant.
• Nozzle flow: Discharge from one nozzle in litres per minute.
• Nozzle spacing: Distance between adjacent nozzles in centimetres.
• Speed: Forward travel speed in kilometres per hour.
  • Worked example: A nozzle discharging 1.2 L/min at 50 cm spacing and 6 km/h gives 600 × 1.2 / (50 × 6) = 24 L/ha. Increasing speed reduces the application rate if pressure and nozzle flow remain unchanged.
  • Droplet behavior: Fine droplets improve coverage but drift more easily; coarse droplets reduce drift but may give poorer coverage on difficult targets.

C. Types

Sprayers are classified according to the source of pressure, method of carrying, and means of producing airflow or movement.

• Hydraulic sprayers: Use pump pressure alone to force liquid through nozzles; common examples include tractor-mounted boom sprayers.
• Compression sprayers: The tank is partly filled and pressurized with air before spraying.
  • Use: Suitable for gardens, nurseries, and small areas.
  • Limitation: Pressure falls during operation, so spray output gradually changes.
• Knapsack sprayers: A 10–20 L tank is carried on the operator’s back and pressurized by a hand-operated lever.
  • Use: Useful for small farms, orchards, and spot treatment.
  • Limitation: Output depends on pumping rhythm and operator fatigue.
• Rocking or lever-operated sprayers: A hand lever operates a piston pump, often from a stationary position; they are useful where a knapsack unit is unsuitable.
• Motorized knapsack sprayers: A small engine operates the pump and may provide a continuous spray at higher output than hand-operated units.
• Mist blowers: Use an engine-driven fan to carry fine droplets in an air stream, allowing penetration into foliage and orchard canopies.
  • Limitation: Fine droplets are highly susceptible to wind drift.
• Air-blast sprayers: A powerful fan carries spray through a large air volume toward trees and dense crops; they are common in orchards.
• Boom sprayers: Several nozzles are mounted on a horizontal boom for uniform treatment of field crops.
• Hand sprayers and spray guns: Deliver a directed jet or fan from a lance and are used for spot spraying, livestock premises, and localized treatments.

D. Maintenance

Proper maintenance preserves application accuracy, prevents chemical exposure, and extends the service life of the sprayer.

• After each operation: Drain unused mixture according to label instructions and rinse the tank, hoses, boom, and nozzles with clean water.
• Nozzle care: Remove nozzles and strainers and wash them with a soft brush; never use wire or a pin because enlarging the orifice changes the discharge rate.
• Filter cleaning: Clean suction and line filters regularly; a blocked filter reduces flow and can cause uneven spraying.
• Pump inspection: Check oil level where applicable, diaphragm or piston condition, seals, and abnormal vibration or noise.
• Pressure system: Test the pressure gauge and regulator; fluctuating pressure indicates air leakage, worn pump parts, or a blocked line.
• Leak prevention: Replace cracked hoses, loose clamps, damaged gaskets, and worn nozzle caps before operation.
• Calibration check: Collect nozzle output for one minute and compare nozzles; a nozzle differing substantially from the average should be cleaned or replaced.
• Storage: Store the machine clean and dry, protect it from direct sunlight, and drain water from the pump during freezing conditions.
• Operator safety: Wash contaminated clothing separately, remove pesticide residue from exposed surfaces, and keep the equipment away from food and drinking-water containers.

III. Dusters — Dry Powder Application Equipment

A. Components

A duster is a plant protection machine that meters dry pesticide powder and disperses it as a cloud or stream over the target.

• Hopper: Stores the dust formulation and should have a cover to prevent moisture entry and accidental spillage.
• Agitator: Breaks bridges and loosens compacted powder so that material feeds continuously from the hopper.
• Metering device: Controls the quantity of dust leaving the hopper.
  • Slide gate or rotary feeder: Varies the opening or feeding speed.
  • Calibration control: Sets the approximate discharge in kilograms per minute.
• Delivery tube: Carries dust from the metering unit to the outlet; smooth internal surfaces reduce clogging.
• Fan or blower: Produces the air stream that carries and disperses the powder in many mechanical dusters.
• Dust outlet or nozzle: Directs the dust toward the crop; several outlets may be fitted to cover a row or boom width.
• Power source: May be a hand-operated crank, wheel-driven mechanism, electric motor, or petrol engine.
• Frame and carrying arrangement: Supports the hopper and permits use as a hand duster, knapsack duster, or tractor-mounted machine.
• Strainer or screen: Removes lumps and foreign material before they reach the metering outlet.

B. Working

A duster works by regulating a dry pesticide feed and carrying the particles to the crop with mechanical movement or an air stream.

• Loading: The hopper is filled with a dry, free-flowing formulation; damp powder is likely to bridge and produce an irregular rate.
• Agitation: An agitator keeps the material loose and moves it toward the metering opening.
• Metering: A gate, rotary feeder, or vibrating mechanism releases a controlled mass of powder.
• Dispersal: In a blower-operated duster, the fan mixes the powder with air and sends it through the outlet as a cloud.
• Targeting: The outlet is directed toward foliage, plant rows, or a localized pest area; slow, steady travel improves uniformity.
• Rate calculation: If a machine releases m kilograms during a test run over a treated area A hectares:

Dust application rate (kg/ha) = m / A

• m: Mass of dust discharged, in kilograms.
• A: Area covered during the test, in hectares.
  • Worked example: If 2.4 kg of dust is discharged while treating 0.08 ha, the rate is 2.4 / 0.08 = 30 kg/ha.
  • Environmental effect: Dust is easily carried away by wind; application is generally most effective in calm conditions with adequate humidity.

C. Types

Dusters differ mainly in their power source, carrying method, and mechanism for dispersing the powder.

• Hand rotary or crank dusters: A hand crank operates a rotary fan and feeder; they are inexpensive and suitable for small plots or spot treatment.
• Plunger or bellows dusters: Repeated squeezing of a bellows produces air that carries powder through a delivery tube; they are useful for gardens and individual plants.
• Knapsack dusters: The hopper is carried on the back and a hand lever or crank operates the fan and feeder.
  • Advantage: Portable and suitable for small farms and irregular fields.
  • Limitation: The application rate depends on the operator’s movement and maintenance of the crank.
• Wheel-operated dusters: Wheel rotation powers the metering mechanism as the machine moves; output is linked more closely to travel distance.
• Power-operated dusters: An engine or electric motor drives the fan, allowing higher output and better coverage than hand-operated units.
• Tractor-mounted dusters: Mounted on a tractor and used for larger areas, with outlets arranged to cover crop rows.
• Air-blast dusters: Use a high-volume air stream to carry dust into dense foliage or orchard canopies.
  • Limitation: They can create considerable drift and should not be used near people, livestock, water, or susceptible crops.

D. Maintenance

Duster maintenance focuses on keeping the powder path dry, the metering mechanism accurate, and the operator protected from accumulated pesticide.

• Hopper cleaning: Empty the hopper after use and remove residual powder with a dry brush or approved cleaning method; moisture causes caking.
• Metering mechanism: Inspect gates, rotary feeders, agitators, and springs for wear; worn parts alter the discharge rate.
• Air system: Clean the fan, air inlet, and delivery tube so that reduced airflow does not produce incomplete or uneven spreading.
• Blockage removal: Stop the machine before clearing a blocked outlet and use a tool or brush rather than bare hands.
• Calibration: Measure the discharge over a known distance or time and adjust the gate until the required kg/ha is obtained.
• Moving parts: Lubricate bearings, gears, chains, and crank mechanisms according to the manufacturer’s instructions.
• Structural checks: Tighten frame fasteners, inspect straps, and replace cracked hopper covers or delivery tubes.
• Storage: Keep the duster dry, covered, and separate from seed, feed, fertilizer, and household materials.
• Safety cleaning: Wear gloves, protective clothing, and respiratory protection while handling residues; never blow pesticide dust from the machine with the mouth or compressed air directed toward the body.
• Final inspection: Before the next operation, confirm that the feeder, outlet, fan, and carrying straps work correctly and that no powder leaks from joints.