Unit 5: Plant Protection Equipment - Subjective Questions

Definition: A sprayer is a plant protection machine used to convert a liquid pesticide formulation into droplets and distribute them uniformly over a target area.

Main functions:

• Atomization: Breaks the spray liquid into droplets of the required size.
• Pressure development: Produces sufficient pressure to force liquid through the nozzle.
• Metering: Regulates the quantity of spray liquid discharged per unit time.
• Distribution: Deposits droplets uniformly on crops, weeds, soil, or other targets.
• Agitation: Keeps pesticide ingredients uniformly mixed in the tank.
• Control: Allows the operator to start, stop, and regulate the spray.

Sprayers are commonly used for applying insecticides, fungicides, herbicides, plant growth regulators, and liquid fertilizers.

The major components of a hydraulic sprayer are:

• Tank: Stores the spray solution and is generally provided with a filling opening, strainer, drain plug, and level indicator.
• Agitator: Keeps the pesticide uniformly mixed and prevents settling of wettable powders.
• Pump: Draws liquid from the tank and supplies it under pressure.
• Strainers or filters: Remove foreign particles and protect the pump, valves, and nozzles from blockage.
• Pressure regulator: Maintains the required operating pressure and returns excess liquid to the tank.
• Pressure gauge: Indicates the pressure in the delivery line.
• Air chamber: Reduces pressure fluctuations in reciprocating pump systems.
• Hose and delivery pipe: Carry pressurized liquid to the spray lance or boom.
• Cut-off valve: Starts or stops liquid flow.
• Nozzle: Meters, atomizes, and forms the desired spray pattern.
• Boom or lance: Supports and positions one or more nozzles at the required height and spacing.

A hydraulic sprayer works by forcing spray liquid through a small nozzle opening under pressure.

Working sequence:

1. The pesticide and water are mixed in the tank in the recommended proportion.
2. An agitator maintains a uniform concentration throughout the mixture.
3. The pump draws liquid from the tank through the suction strainer.
4. The pump increases the liquid pressure and sends it to the delivery line.
5. The pressure regulator maintains the selected operating pressure and bypasses excess liquid back to the tank.
6. When the cut-off valve is opened, pressurized liquid moves through the hose and lance or boom.
7. At the nozzle, the liquid is metered and broken into droplets.
8. The nozzle pattern distributes the droplets over the target surface.

The application rate depends mainly on nozzle discharge, operating pressure, nozzle spacing, and forward speed.

Classification according to power source:

• Manually operated sprayers: Hand atomizer, hand compression sprayer, rocker sprayer, and knapsack sprayer.
• Animal-drawn sprayers: Ground-wheel-driven field sprayers.
• Power-operated sprayers: Power sprayer, tractor-mounted sprayer, and self-propelled sprayer.
• Aerial sprayers: Spraying systems fitted to aircraft or drones.

Classification according to method of atomization:

• Hydraulic sprayers: Liquid is forced through a nozzle under pressure; examples include knapsack and boom sprayers.
• Air-carrier or air-blast sprayers: High-velocity air carries droplets to the crop; commonly used in orchards.
• Pneumatic sprayers: High-speed air atomizes the liquid at the nozzle.
• Centrifugal sprayers: A rotating disc or cage produces droplets by centrifugal force.
• Electrostatic sprayers: Electrically charged droplets are attracted to plant surfaces.

The appropriate type is selected according to crop geometry, target pest, area, spray volume, and available power.

Construction: A knapsack sprayer consists of a tank carried on the operator's back, straps, a hand-operated lever, piston or diaphragm pump, air chamber, agitator, suction strainer, hose, lance, cut-off valve, and nozzle.

Working:

• The tank is filled with filtered spray solution.
• Movement of the lever operates the pump.
• The pump draws liquid from the tank and delivers it under pressure to the air chamber.
• Compressed air smooths the flow of liquid.
• Opening the cut-off valve allows liquid to pass through the nozzle and form a spray.

Advantages:

• Portable and simple to operate.
• Suitable for small farms and row crops.
• Low initial cost.
• Can operate in fields inaccessible to tractors.

Limitations:

• Low field capacity.
• Operator fatigue is high.
• Pressure and discharge may fluctuate.
• Uniform application depends strongly on operator skill.

Comparison:

• Reciprocating pumps provide positive displacement and require pressure-relief arrangements.
• Diaphragm pumps isolate working parts from the chemical liquid.
• Centrifugal pumps are simple, compact, and provide smooth flow but are not suitable for very high pressure.
• Pump selection depends on required pressure, discharge, chemical compatibility, and maintenance facilities.

Functions of a nozzle:

• Controls the liquid discharge rate.
• Atomizes liquid into droplets.
• Produces a specific spray pattern.
• Directs droplets toward the target.
• Influences coverage, drift, and penetration.

Hollow-cone nozzle:

• Produces a circular ring-shaped pattern.
• Forms relatively fine droplets.
• Provides good foliage coverage and penetration.
• Commonly used for insecticides and fungicides.

Flat-fan nozzle:

• Produces a flat, fan-shaped pattern.
• Requires proper overlap on a boom.
• Commonly used for broadcast herbicide application.

Flood-jet nozzle:

• Produces a wide-angle pattern with coarse droplets.
• Operates effectively at relatively low pressure.
• Has lower drift risk but less uniformity when incorrectly spaced.
• Used for fertilizers and some soil-applied herbicides.

Factors affecting droplet size:

• Nozzle orifice size: A larger orifice generally produces larger droplets at the same pressure.
• Operating pressure: Increasing pressure usually produces smaller droplets.
• Nozzle design: Cone, fan, air-induction, and centrifugal nozzles produce different droplet spectra.
• Liquid properties: Viscosity, density, and surface tension affect atomization.
• Nozzle wear: Wear enlarges the orifice and increases discharge.

Factors affecting deposition:

• Wind speed and direction.
• Temperature and relative humidity.
• Boom height and nozzle orientation.
• Crop canopy and target position.
• Forward speed and spray volume.

Practical significance: Fine droplets provide good coverage but are highly susceptible to drift and evaporation. Coarse droplets reduce drift but may provide inadequate coverage for contact pesticides. The operator must therefore select a droplet size that balances coverage, penetration, retention, and environmental safety.

Calibration ensures that the recommended quantity of pesticide is applied uniformly.

Procedure:

1. Inspect the sprayer, clean the filters, and check all nozzles.
2. Fill the tank with clean water.
3. Set the recommended pressure and measure the discharge of each nozzle for a fixed time.
4. Replace a nozzle if its discharge differs significantly from the average.
5. Measure the effective spray width.
6. Operate the sprayer over a measured distance and determine the actual forward speed.
7. Calculate the application rate and adjust pressure, nozzle size, or speed if required.

If total boom discharge is L/min, effective width is m, and speed is km/h, then:

For nozzle calibration, if nozzle discharge is L/min and nozzle spacing is m:

The constant converts the units to litres per hectare. Calibration should be performed under conditions similar to actual field operation.

The application rate is calculated using:

where:

• = application rate in L/ha,
• L/min,
• m,
• km/h.

Substituting the values:

Therefore, the sprayer applies L/ha.

The application rate can be reduced by:

• Increasing the forward speed within safe operating limits.
• Using nozzles with smaller discharge ratings.
• Reducing operating pressure, provided the spray pattern remains satisfactory.
• Increasing effective spray width where equipment design permits.

Changing nozzle size is generally more reliable than making a large pressure adjustment because pressure also affects droplet size and drift.

After each use:

• Empty the remaining spray liquid according to pesticide safety recommendations.
• Rinse the tank, pump, hoses, filters, boom, and nozzles with clean water.
• Use an appropriate cleaning agent when required by the chemical label.
• Operate the sprayer briefly with clean water to flush all lines.
• Remove and clean strainers and nozzle tips with a soft brush.
• Check for leaks, loose fasteners, damaged hoses, and worn seals.

Periodic maintenance:

• Lubricate moving parts as recommended by the manufacturer.
• Check pump oil level where applicable.
• Inspect the pressure gauge and regulator.
• Measure nozzle discharge and replace worn nozzles.
• Examine belts, bearings, valves, and air chambers.

Storage:

• Drain the equipment completely.
• Release pressure from the system.
• Protect metal parts against corrosion.
• Store the sprayer in a dry, shaded, secure place.
• During freezing conditions, drain all water or use an approved antifreeze procedure.

Nozzle openings should never be cleaned with wire or a sharp metal object because this changes the orifice shape and discharge rate.

Definition: A duster is a plant protection machine used to apply pesticides in dry, finely divided powder form to crops or soil.

Working principle:

• Dust pesticide is stored in a hopper.
• An agitator prevents bridging and maintains a continuous flow.
• A metering mechanism regulates the quantity of dust leaving the hopper.
• A fan or blower generates an air stream.
• The measured dust enters the air stream and becomes suspended in it.
• The air-dust mixture moves through the delivery tube and is discharged through an outlet or nozzle.
• The dust settles on the target surfaces due to impaction, interception, gravity, and electrostatic attraction.

Effective dusting requires dry powder, calm weather, proper metering, and suitable air velocity.

The principal components of a power duster are:

• Hopper: Holds the pesticide dust and is shaped to promote continuous flow.
• Lid and screen: Prevent contamination and stop large foreign particles from entering.
• Agitator: Breaks lumps, prevents bridging, and keeps dust flowing toward the outlet.
• Metering mechanism: Controls the rate at which dust leaves the hopper.
• Fan or blower: Produces the air stream required to carry the dust.
• Power source: Drives the blower and other moving parts; it may be an engine, tractor PTO, or electric motor.
• Feed tube or venturi: Introduces metered dust into the moving air stream.
• Delivery hose: Carries the air-dust mixture to the outlet.
• Nozzle or discharge spout: Directs and distributes dust over the target.
• Control lever: Starts, stops, or regulates dust delivery.
• Frame and carrying arrangement: Supports the components and permits mounting, transport, or carrying.

Common types of dusters:

• Plunger duster: A hand-operated plunger forces air through a chamber. The air picks up a measured quantity of dust and discharges it through a tube. It is suitable for kitchen gardens and spot treatment.
• Bellows duster: Compression and expansion of bellows generate airflow. It is simple and suitable for small-scale application.
• Rotary hand duster: A hand crank rotates a fan that produces continuous airflow. Dust is metered from the hopper into this stream.
• Knapsack duster: The unit is carried on the operator's back. A manually or mechanically driven blower carries dust through a hose and nozzle.
• Power duster: An engine or motor drives a high-speed blower. It provides greater discharge, range, and field capacity.
• Tractor-mounted duster: A tractor PTO drives the blower and metering mechanism. It is used for large field areas.
• Aerial duster: Dust is distributed from aircraft or drones over extensive or inaccessible areas.

Selection depends on field size, crop type, required output, available power, and the need for canopy penetration.

Working:

1. Pesticide dust is placed in the hopper.
2. The operator turns the crank at a nearly uniform speed.
3. The crank drives a rotary fan, which produces a continuous air stream.
4. An agitator keeps the dust loose and prevents bridging.
5. The metering opening releases a controlled quantity of dust.
6. Dust enters the air stream, becomes suspended, and travels through the delivery pipe.
7. The nozzle directs the air-dust mixture toward the crop.

Factors affecting performance:

• Crank speed and resulting air velocity.
• Size and setting of the metering opening.
• Dust particle size, moisture content, and flowability.
• Condition of the fan and agitator.
• Length and condition of the delivery hose.
• Wind speed, humidity, and crop density.
• Operator walking speed and nozzle movement.

Uniform operation is essential because changes in cranking or walking speed directly affect the application rate.

Spraying is generally preferred where water is available and accurate deposition is required. Dusting is useful where water is scarce, rapid treatment is needed, or wet application is unsuitable.

Calibration procedure:

1. Clean and inspect the hopper, agitator, metering device, blower, hoses, and outlets.
2. Fill the hopper with a known mass of dust formulation.
3. Select a metering setting and operate the duster at the normal blower or crank speed.
4. Travel over a measured distance at the intended field speed.
5. Weigh the dust remaining in the hopper or collect and weigh the discharged dust.
6. Determine the effective width covered.
7. Calculate the treated area and application rate.
8. Adjust the metering opening or travel speed and repeat until the recommended rate is obtained.

If kg of dust is discharged over distance m with effective width m, then:

Calibration should be conducted using the actual dust formulation because particle size, moisture, and flow characteristics influence discharge.

Maintenance after operation:

• Empty unused dust into a correctly labelled container if permitted by the product instructions.
• Remove dust deposits from the hopper, metering mechanism, fan, hoses, and outlets.
• Clean the machine by brushing or using a suitable low-pressure air method in a safe area.
• Keep the duster dry because moisture causes caking, corrosion, and blockage.
• Inspect the agitator and metering mechanism for wear or jamming.
• Check the fan blades, bearings, belts, seals, and fasteners.
• Replace cracked hoses and damaged discharge outlets.
• Lubricate bearings and moving parts according to the manufacturer's instructions.

Storage practices:

• Store the duster empty, clean, and dry.
• Close or cover all openings to prevent entry of dirt and moisture.
• Protect metal surfaces from corrosion.
• Store the machine away from food, animal feed, seed, and living areas.
• Keep pesticide residues and equipment inaccessible to children and unauthorized persons.

Before application:

• Read the pesticide label and follow the recommended dose, equipment, and waiting period.
• Wear suitable personal protective equipment, including gloves, protective clothing, boots, eye protection, and an approved respirator where required.
• Inspect and calibrate the equipment using clean water or a safe substitute.
• Check weather conditions and avoid strong wind, rain, and excessive heat.

During application:

• Keep people, livestock, and pollinators away from the treatment area.
• Avoid spraying or dusting against the wind.
• Prevent drift toward water bodies, houses, roads, and sensitive crops.
• Do not eat, drink, smoke, or touch the face while handling pesticides.
• Stop the machine and release pressure before clearing a blockage.
• Never blow through a nozzle or dust outlet with the mouth.

After application:

• Dispose of rinsate, residues, and containers according to regulations and label instructions.
• Wash equipment at an approved location away from wells and surface water.
• Wash hands and body thoroughly and launder contaminated clothing separately.
• Record the product, dose, field, date, weather, and operator details.

Correct equipment selection, calibration, and maintenance reduce operator exposure, crop injury, pesticide waste, drift, and environmental contamination.