Pesticides are applied on crops to keep the pests under minimum biological activity. Insecticides are used against insect pests, fungicides are used against fungal crop diseases and herbicides are used against weeds in order to protect crops and avoid losses.
It is necessary to select the most efficient equipment for securing a uniform deposit on the target in the least time with minimum labour and without appreciable wastage of material. The concentration and quantity of the spray fluid or dust material to be applied will depend upon the type of machinery used.
The efficacy of a machine depends upon its ability to give the maximum pest control per unit area and time with the minimum dose of actual ingredient of the poison. The wastage and pollution of the environment should also be the minimum. Pesticides may be applied as dusts, sprays, mists, aerosols, smokes, etc. Various types of equipment used include dusters, sprayers, agricultural aircrafts, granule applicators, soil injectors, etc.
Type # 1. Dusters:
Appliances that are used to distribute dust formulations are known as dusters. These dusters may be manually operated or power operated.
I. Manually Operated Dusters:
There are several types of manually operated dusters that are available in the market.
Some of the important ones are described here:
(i) Plunger Duster:
It is made up of air pump, dust chamber and a discharge assembly. The duster is held by one hand and is pumped with the other hand. The air pumped in creates a dust cloud which passes through the delivery vent. The amount of dust to be applied can be controlled by the speed at which plunger is forced and by adjusting orifice at the vent. These are easy to operate and are quite inexpensive and are useful for dusting in households and kitchen gardens. These are also used for spot-treatments against ants, poultry pests and external parasites of farm animals.
(ii) Bellows Duster:
These can be carried in hand as well as on the back and the air blast is created by operating the bellows. It has a small container for dust, which is fed to the air stream, thus producing a dense cloud.
(iii) Rotary or Fan Duster:
It has an enclosed fan geared to a hand crank and a hopper holding the dust. The high speed gear transmits the velocity to a blower and the dust cloud enters the atmosphere through spreader nozzle. The dust is carried by wind and it falls on the target. These machines are useful for dusting on crops like paddy growing in standing water.
(iv) Wet Dusting Equipment:
In this type, while the dust is passing, a fine discharges of water mixes with it before reaching the target. This dust adheres better on the crop surface than the ordinary dust and drift is also reduced. This machine is more suitable for semi-arid zones.
II. Power Operated Dusters:
(i) Tractor Mounted Duster:
It is also known as power take off duster. This duster is mounted on a tractor and the power to operate the duster is taken from tractor with the help of a V-belt. The dust flows through eight nozzles mounted on a boom. The speed of fan producing the blast varies with that of the tractor; so it is difficult to maintain a uniform discharge. The machine can carry 20- 45 kg dust.
(ii) Engine-operated Duster:
These dusters are operated with an internal combustion four stroke engine of 1-3 hp. Larger dusters are also available with power up to 25 hp. These can be held in hand, can be carried on back (knapsack type) or can be carried on a stretcher or trolley, depending upon the size and the use.
In these dusters the fan normally has a speed of 2,200- 3,400 rpm and delivers 14.56-28.00 m3/min of air at velocities of 80-260 kmph. These dusters are suitable for dusting trees and large fields. Some of the tractor trailor dusters have booms up to 9 metres with as many as 18 delivery nozzles.
Type # 2. Sprayers:
A sprayer is an appliance which atomizes the spray fluid, which may be a suspension, an emulsion or a solution. The fluid is ejected with some force for proper distribution. The various types of sprayers can be grouped into four categories, depending upon the volume of spray fluid discharged to cover a unit area.
Categories of Sprayers:
(i) High Volume (HV):
These require 300-500 litres per ha of spray fluid normally and some-times even up to 800-1000 litres per ha, depending upon the size of the crop. These are the most versatile sprayers. The size of spray droplets ranges between 300-500 µm and the density is 10-20 droplets per cm2. There are many such sprayers, for example, foot sprayer, stirrup sprayer, knapsack sprayer, hand compression sprayer, rocker sprayer, etc.
(ii) Low Volume (LV):
These sprayers require 50-100 litres of spray fluid per ha. They are normally motorized knapsack sprayers. The size of droplets ranges between 100-300//m and the density is 30-50 droplets per cm2.
(iii) Ultra Low Volume (ULV):
These sprayers require 1-5 litres per ha of spray fluid. Normally special formulations are available which are used without any dilution. The size of spray droplet ranges between 60-100 µm and their density is 50-70 droplets per cm2. The fogair, knapsack mist blowers, with restrictors, are included in this category.
(iv) Aerosols:
Less than 1.0 litre per ha of spray fluid is required to create fog. Aerosols are applied normally in enclosed places. The size of droplets ranges between 1-50 µm and density is 70-350 droplets per cm2. The examples are pressurised containers, swing fog machine, etc.
Various types of droplet spectra are adopted for different situations. Most of the flying insects require very fine spray having particle size 10-30 µm. For locusts and forest insects, a spectrum of 20-60 µm is most suitable. Most herbicidal sprays have a spectrum of 400-1000 µm which gives minimum drift. The droplet spectra are generally classified as given in Table 7.2.
Types of Nozzles:
There are various types of nozzles to disperse the spray fluids. Nozzles are usually classified and named after the energy used to form droplets.
(i) Hydraulic Nozzles:
These nozzles are mostly used in sprayers in which large quantities of water are used in spray fluid. The liquid under pressure is fed through a nozzle. The pressure determines the rate of discharge, throw of the fluid and its atomization.
These nozzles usually produce coarse sprays and are of following types:
(a) Impact or Floodjet Nozzles:
These operate at low pressures of 0.5-1 kg per cm2 giving a coarse spray without any drift. These are used for spraying herbicides and liquid fertilizers.
(b) Flat Fan Nozzles:
These are supplied with variable discharge rates varying from 500 to 3,000 ml per min at different angles (60-110°). Those most commonly used have a discharge of 1,500 ml per min at a pressure of 3 kg per cm2and an angle of 80°. These also give fine to coarse sprays without much drift and are more suitable for insecticidal and fungicidal spray for a good coverage.
(c) Cone Nozzles:
Generally, hollow cone nozzles rather than solid cone nozzles are used in agriculture. These are suitable for the application of insecticides and are most widely used because of their low price.
(ii) Gaseous/Pneumatic Nozzles:
These are usually used with mist blowers. The atomization occurs by the impact of air blast on the drop of a pesticide falling with gravity. The ratio of fluid discharge to air is 1 to 1000 times for appropriate atomization. These nozzles provide fine sprays suitable for low volume spraying.
(iii) Centrifugal Nozzles:
The spray fluid is fed to a rotating disc and the centrifugal force disintegrates it into droplets of very fine size. The nozzle is used in rotatory disc ULV sprayers. The droplet size is inversely proportional to the speed and the size of the disc.
(iv) Thermal or Hot Tube Nozzles:
A fog composed of very fine droplets can be produced by condensing a pesticide which has been injected into a stream of hot gas to shear the liquid into droplets which are immediately vaporized. These vapours later on condense into very fine droplets which are suspended in the air for sometime till they finally settle on a surface. This method is very suitable for controlling flying insects in enclosed spaces.
Types of Sprayers:
I. Manually Operated Sprayers:
These are of two types, i.e., pneumatic and hydraulic.
(i) Pneumatic Sprayers:
(a) Hand Compression Sprayer:
The spray fluid is filled in a tank above which there is an air pressure, created with the help of a built-in air pump (Fig. 7.5). After all the solution is discharged through the nozzle, the air is released before the tank can be refilled. Since pressure drops with the lowering of fluid level in the tank, occasional pumping is required. These are small spray pumps and are suitable for kitchen gardens and houses. These pumps carry 0.5-1.0 litre fluid. The body of the pump can be made of polyvinyl carbonate or of a metal with an anti-corrosion coating.
(b) Pressure Retaining Pumps:
There is an air chamber which is filled with air under pressure and then liquid is pumped with the help of a charge pump. Because of continuous and constant pressure at the nozzle, a uniform discharge and droplet size is maintained throughout the operation. The lance is also provided with a regulation to have uniform discharge.
In a knapsack battery sprayer, for example, a pressure of 4-5 kg per cm2 is developed with a pump mounted on the sprayer itself. The tank capacity is 10-20 litres and the liquid is discharged at a constant rate. These are low volume sprayers requiring 250-300 litres spray fluid for one hectare. One person can spray one ha per day with 15-20 refillings.
(c) Small Pneumatic Atomizers:
These pumps have a small container of 250 ml and there is a pump mounted on it externally. On working the pump handle there is a direct fine discharge. These machines are most suitable for controlling household pests like mosquitoes, houseflies, etc., by keeping the doors and windows shut for a while. These are made of polyvinyl carbonate as well as of tin metal. The fluid should be removed from container after use.
(ii) Hydraulic Sprayers:
(a) Knapsack Sprayer:
The tank in this sprayer is not pressurized but is provided with a shut off regulator. It has a plunger or a diaphragm pump which is mounted either outside or inside the tank, and is immersed in the spray fluid (Fig. 7.6). The pump is operated by a hand lever under the arm. Newer models are now equipped with solid piston type pumps instead of the plunger type.
Continuous pumping is necessary to have a uniform discharge. The capacity of the tank varies from 15 to 20 litres. One person can work this sprayer independently and can cover one ha of normal crop in one day, with 15-20 refillings. It is a medium volume sprayer, requiring 350-450 litres of spray fluid per ha.
(b) Foot Sprayer:
It is a high volume sprayer and is also known as the pedal pump. It is worked by up and down movements of the foot of an operator. It has one suction outlet but two delivery tubes, lances and nozzles which are handled by two men. Constant pedaling is required to develop a continuous pressure up to 17-21 kg/ cm2.
This sprayer is also suitable for tall crops. It requires 500-1000 litres water per ha depending upon the growth of a crop and four persons are needed to operate it. One person pedals, two persons hold the lances for spray and fourth person prepares the spray fluid and also acts as a reliever to the pedaller. With this pump, 2 hectares can be sprayed in a day.
(c) Rocker Sprayer:
It is also a high volume sprayer requiring 500-750 litres of spray fluid per ha. It is very similar to the foot sprayer but is operated by a long hand lever. The pump may be either of single action or of double action type but in both cases continuous pumping is necessary for a uniform discharge. It can develop a pressure up to 14-18 kg per cm2 and can also be used for spraying trees up to 5 m height. Normally, two persons are needed for this sprayer and they can cover about 1-2 ha in one day.
(d) Stirrup Pump:
It is a high volume sprayer and is commonly known as bucket pump, because it is worked after placing it in a bucket full of the spray fluid. The pump may have a single barrel or a double barrel. The pump is worked with hand by up and down movements.
It can develop a pressure up to 14 kg per cm2 and can be provided with two delivery tubes, two lances and two nozzles. If there are two lances, then four persons are required to carry out the spray operations and they can cover 2 ha in a day. It requires 500-875 litres water per ha depending upon the crop size.
II. Power Operated Sprayers:
(i) Mist Blower or Motorized Knapsack Sprayer:
It is a low volume sprayer, but with a restriction in the nozzle. It can be converted into an ultra-low volume sprayer. A two-stroke petrol engine drives the blower; a part of the air also pressurizes the chemical tank.
An impeller blows the air through the sprayer nozzle, while the solution separately flows from the liquid tank. The fluid gets atomized at the point of contact with the air blow. The tank capacity is 7-12 litres and the air blast is delivered at the rate of 2.7-9.1 cm3/ min, at velocities ranging from 175-320 kmph.
The discharge rate is variable from 0.5 to 5 ml per min. When used as a low volume sprayer one man can cover 2 ha in one day, using 125-200 litres spray fluid per ha. The swath width is 4-5 m horizontally and 3-4 m vertically. Trolley mounted mist blowers are also available with a much larger tank, having a capacity of 50 litres.
(ii) Tractor Mounted Sprayer:
The pump is driven by the power take-off shaft of a tractor. The sprayer may be mounted on the power lift or on a trailor. It has a big liquid tank of 500-600 litre capacity. The swath width is about 18 m and may carry as many as 18 nozzles on a single boom lance. Two persons are required to conduct the spraying and they can cover upto 4-5 ha in a day. The crop should be in rows and it should be just as tall as the clearance of body of tractor allows. These pumps are comparatively less expensive but are very versatile in use.
(iii) Power Sprayers:
These are high volume sprayers and can be mounted on a stretcher, a wheel barrow, a tractor or a truck. These sprayers usually have hydraulic pumps of the piston type. The power is supplied by a four-stroke petrol engine. It has one or two delivery hoses. A delivery hose may be 7-30 m long which ends into a hand-operated spray gun with a regulator.
The pumps operate at pressures upto 56 kg/cm2 and have a discharge capacity of 6.8 to over 273 litres/min and carry 180-3,600 litres of spray fluid, depending upon the size of tank and the engine. The sprayers are commonly used for applying pesticides, fertilizers, plant hormones, etc. on shade trees, fruit plants or ornamentals.
(iv) Ultra Low-Volume Sprayers:
The first trial with ultra-low volume (ULV) sprayers was carried out in USA in 1962 for the control of grasshoppers. In 1964, technical malathion was used successfully at the rates of 850-1125 ml per ha for the control of cotton boll weevil. Since then a lot of progress has been made in this field. The efficiency of these machines depends upon the regulation of a uniform size of the droplets.
If droplets are larger than 150 µm, the coverage will be poor. If droplets are smaller than 30 µm, they will miss the target and cause environmental pollution through drift. In this machine small droplets are propelled at a high velocity so that they reach the target after penetrating the air cushion around the surface to be sprayed.
In motorized knapsack sprayers, nozzle can be fitted with a suitable restrictor for ULV spraying. There is now a number of spinning disc ULV sprayers which run on 12-volt battery. These sprayers are very handy and easy to operate. The droplet falls on a dentate disc spinning at 3,000 rpm.
The speed, the number of dents per unit length and size of disc determine the ultimate size of the droplets created. These sprayers mostly use air currents to disseminate the droplets but these can also be provided with a blower to force the droplets towards the target. This increases the penetration of the droplets through the air cushion for reaching the target surface.
The machines are marketed in various models, for example, overhead sprayer, hand held rotary disc sprayer, chest-mounted rotary disc sprayer, etc. The container can carry up to 1 litre concentrated ULV formulation which may be enough for one hectare.
There are certain modern ULV sprayers in which sonic energy is used to break the droplets. The atomizing nozzle uses sound waves to break the spray fluid into fine droplets. The compressed air is passed through the centre of the nozzle into a resonator cavity; such nozzles are called soni-core nozzles.
The sonic-energy field explodes the passing fluid into a mist of 50-100 µm. It is a very efficient sprayer, and is being marketed by Buffalo Turbine Agricultural Equipment Co., New York, USA. This ULV sprayer is recommended for use in enclosed spaces like a warehouse or a living quarter, for the control of flies, mosquitoes, grain pests and other indoor pests.
The drift and droplet spectrum can be studied by placing stretched parafilms or manganese oxide-coated plates or cellophane tapes at varying distances from the sprayer. The droplets so collected can be used to determine the density and the size of droplets under a microscope, using occular and stage micrometers.
(v) Aerosol Dispensers:
These dispensers have metallic containers to withstand the pressure of liquefied propellant. The droplet size being small (1-50 µm), the particles remain suspended in the air for a long time, which is desirable for controlling flying insects like flies and mosquitoes. These can be used successfully in greenhouses also.
A dispenser is fitted with a delivery tube which remains dipped in the pesticide. When a button having a small orifice is pressed at the top of this tube, the propellant forces its way out along with a fine spray of the pesticide. The propellant most frequently used is an inert gas, dichlorodifluoromethane (Freon-12) or methyl chloride. Aerosol dispensers for pyrethrum, allethrin, DDT, lindane, DDVP, etc. are available.
The popular capacity of an aerosol dispenser is 300-400 g of formulation but 2-5 kg sizes are also available. Aerosols are used at the rate of 7-14 g/100 m3 of space, at 5-10 per cent concentration in the dispenser. Other ways of generating aerosols are through centrifugal energy, compressed air or high velocity hot air pulse jet.
(vi) Smoke Generator:
Solid particles in a smoke are in the range of 0.001 to 0.1 µm. The smoke rises to the top and no enclosure remains untreated. The smoke particles settle down later and the crawling insects usually pick up the lethal doses. The smoke produced by burning insecticides loses killing capacity to some extent. In relatively stable insecticides like DDT and lindane, the loss due to heat may be as much as 30 per cent. Smoke formulations are prepared by mixing the technical material with some slow burning material.
For example, DDT or lindane formulated for slow burning contains 58-60 per cent technical material, a burning mixture of sucrose and potassium chlorate (30-40 %) and a retardant such as clay or diatomaceous earth (2- 10 %). A container having 450 g of this mix will burn for 3 minutes, and treat 450 m3 of enclosed space. These are also commonly called as ‘smoke bombs’. Smokes are used to kill pests of greenhouses, warehouses, industrial establishments and cargo ships.
(vii) Vapour Generators:
These are popularly known as pesticide vaporizers or thermal vapour generators or electric-vaporising devices. These are used in enclosed spaces. Mostly hydrocarbon pesticides like lindane and DDT are held in an electrically heated container at a flash temperature which permits slow but continuous vaporization. It can convert 28 g of pure lindane crystals into vapours in 5 minutes which would be sufficient to kill insects in 280 m3 of space. The vapours act as fumigants.
Type # 3. Agricultural Aircrafts:
An aircraft was first used for pest control in 1920. Since then these have been used for applying pesticides in 40 countries. It is estimated that there are 20,100 aircrafts, which cover 171.4 million hectares annually, throughout the world.
The use of an aircraft enables the coverage of vast areas rapidly, timely and economically. Both the fixed wing aircrafts and the rotary wing aircrafts (helicopters) have been employed for applying pesticides on field crops, orchards, forests, pastures and wastelands. It is also employed most successfully for locust control in desert areas.
There are three types of fixed wing aircrafts:
(i) Light Aircraft:
It is usually monoplanes with ground speed of 100-150 kmph. It has single engine of 90-125 hp.
(ii) Medium Aircraft:
It is usually biplanes with ground speed of 130-300 kmph. It has single engine of 100-450 hp.
(iii) Heavy Aircraft:
It is a biplane with ground speed of 150-250 kmph and has usually two engines of 125-500 hp each. It has the advantage of maintaining altitude even when one of the engines fails. It is a desirable factor for low-level operations.
The rotary wing-aircraft may be a light machine with a single rotor or a heavy machine with large twin rotors. The advantages of helicopters over aeroplanes are ability to land close to the fields to be treated, capacity to hover-over the ‘hot’ spots of pests, accuracy to confine pesticide application to a given field, and greater manoeuvrability.
Operational conditions greatly influence the choice of aircraft. A fixed plane requires 270-450 m of clear landing strip whereas a helicopter can land on a clear piece of land about 30 m2. Further, the spray pattern of a helicopter is better than that of a fixed wing plane in which the wing tips and propeller create air columns and turbulences in the micro-environment that is being sprayed. In addition to this, the spray from helicopter drops at a speed of 48-50 kmph which results in a rebound from the soil surface and thus foliage from top as well as from bottom gets treated.
In other words, coverage of foliage is more thorough in case of helicopter spray and also there is lesser drift and more accurate spraying of the target as compared with that of the fixed-wing aeroplanes. There is also a greater crash safety in case of helicopter for pilots. The major drawbacks of a helicopter are the higher initial cost and high maintenance investment. The cost of a helicopter is 3-4 times that of a fixed wing.
In India, aircraft was used first in 1945 to spray insecticides for the control of mosquitoes in Delhi. Against locusts, the aircraft was used for applying aldrin on ground in 1951 and on flying swarms in 1961 in Punjab. Till 1955, Piper-super cruisers used to be requisitioned for spraying purposes from the flying clubs. Two Beaver aeroplanes were then procured from Canada under the Colombo Plan in 1956-57 for general plant protection and locust control.
Later, one Auster Auto-car was purchased for this purpose. Basant, indigenously developed at Hindustan Aeronautics Ltd., Bangalore is an agricultural aircraft which is in extensive use currently. It has a 400 hp engine and can carry a load of 825 kg. It has proven its versatility in aerial spraying. Currently, there are more than 65 aircrafts engaged in aerial spraying in India.
Aircrafts can be used for conventional as well as for ULV spraying. For conventional spraying, the aircraft is flown at 2-4 m above the crop. It gives a swath width of 20-30 m and the plane uses 20 litres per ha of spray fluid. It can spray 300-400 ha in a day. In case of ULV application, the flying height is increased to 7.5-10 m. It gives a swath width of 30-45 m.
It can cover about 1200 ha in a day. The spray fluid is undiluted or special LVC formulations are used. The tank capacity varies from 160 to 900 litres depending upon the type of aircraft. The spray pump is normally centrifugal type generating 3.5 kg per cm2 pressure; it may be motor driven, propeller driven or it may derive power from the aircraft.
The size of a boom varies between 10-15 m and there may be 30-35 nozzles to cover a swath width of 30-45 metres. The volume median diameter (VMD) of droplets varies between 100-150 µm. Hydraulic, pneumatic or centrifugal rotary nozzles are used in aeroplanes.
Besides spraying, aircrafts can be used for applying dusts also. An aircraft can carry 90-900 kg of dust. Wind powered agitator is provided for uniform flow of the dust. There is an adjustable air- vent in the hopper for discharge regulation. Dusting is carried out at greater height than spraying, for obtaining a uniform distribution. Normally, aerial dusting is not as effective as spraying.
Type # 4. Miscellaneous Machinery:
i. Granule Applicator:
Placement of insecticidal granules in the whorls of crops like maize, jowar, etc. is very effective for the control of stem borers. To place granules at the right spot, a hand held granule applicator is required. The capacity of container is 500 g to 1 kg. The lid of container is perforated and is adjustable to deliver granules. Sometimes, the container is provided with a long lance which ends into an orifice which is provided with a spring hook for keeping the hole in closed position.
A clutch through a wire is used to open the hole and a lance guides the granules to the desired place. It is also good for applying granules in burrows. One person can cover 0.25 ha in a day. There is one knapsack granule applicator which has a similar device except that the hopper is large and is mounted on the back. The capacity of hopper is 10 kg.
There is a special applicator designed for palm trees in which case the hopper is at the top of the lance in inverted position. There is a sickel blade along with hopper to cut leaf axil so that granules can be dispensed at the correct place in palm trees.
ii. Soil Injectors:
Most soil fumigants are liquids and are applied with soil injectors. Handheld soil injectors with a capacity of 2-3 litres are commonly used to inject fumigants up to a depth of 15-22 cm, for controlling soil insects and nematodes. One person can treat about 0.25-0.5 ha in a day by selective spot treatment.
Tractor-drawn soil injectors are in regular use in advanced countries. The injectors are placed along with the harrow to direct the liquid into the furrow. These injectors get the supply from a tank mounted on the tractor. Similar injectors can be used for applying liquid ammonia in the soil as a fertilizer.
There are certain injectors which are used to control rats. These injectors have a container which is connected with plunger pump. There is a rubber tube about 1 m in length attached with the container. When plunger is worked, the air escapes through the tube connected with container. This carries a load of dry fumigant.
The rubber tube is inserted in a live burrow and pitted with soil. After injection, the rubber tube is pulled out and the hole is plugged with soil. For rat control, calcium cyanide dust is used which on coming in contact with soil moisture releases hydrogen cyanide gas, which is a deadly poison.