Chapter 8

EQUIPMENT AND CALIBRATION


Many over-the-counter pesticides for household and garden use are sold in a form ready for application. Solid products are often spread simply by sprinkling from the boxes in which they are furnished, and some liquid products can be sprayed from simple, small pressurized equipment. Several pesticides used for vector control are available in granular forms that can be applied by hand or through commonly available equipment like fertilizer spreaders or horn seeders. Other pesticides used in vector control require specialized equipment for their application. Some public health pesticides come in concentrated form and must be diluted to produce what is known as a tank mix. Mosquito adulticides that are applied as fogs or by using ultra-low volume techniques require equipment designed for these purposes. Because the labels of the pesticides used in these kinds of applications carry specific restrictions on droplet size and application rates, it is critical that the equipment be maintained in good working order, and that the equipment is calibrated frequently to make sure the applications conform to label requirements.

The first question that needs to be asked when choosing the type of pesticide application equipment to be used in vector control operations is whether a liquid or a solid (dust or pellets) pesticide formulation will be used. For liquid formulations, the basic choice will hinge on the spray techniques to be used. Spray techniques, in turn, often are classified on the basis of the spray volume used in an application. The three basic types of liquid spray techniques are high volume (40 gallons per acre or more), low volume (0.5–40) gallons per acre), and ultra-low volume (0.5 gallons per acre or less).

Pesticide Application Equipment

The type of application device to be used for a specific job should be selected after careful consideration of the location and size of the area to be treated and the pest to be controlled. There are two basic types of equipment used to apply public health pesticides: powered and unpowered.

Unpowered Equipment

Generally, unpowered equipment is suitable for relatively small pesticide applications, such as spot treatments of aquatic sites where mosquito larvae are present. Typical unpowered equipment for liquid pesticides includes the some backpack and tank sprayers. Sometimes these types of equipment are called compression sprayers. Unpowered backpack sprayers are really just tank sprayers with straps to permit them to be carried like a backpack. These sprayers sometimes have a continuously operated pump lever to maintain pressure in the pesticide tank. Others are pumped up by hand until pressure reaches a certain point. The pesticide then can be sprayed until the pressure drops below the level where the sprayer works effectively. Then it must be re-pressurized. Pressurized tank sprayers and backpack sprayers come in sizes ranging from about 1–5 gallons. Sprayers that are not backpack types are often referred to as "hand can, or by their capacity, such as a "3-gallon sprayer."

Pesticides in solid form (granules, slow release briquettes, powders, etc.) can be applied by hand, with small crank-operated spreaders, dust cans, or similar devices. Aerosol bombs are also unpowered pesticide applicators.

Small unpowered equipment is inexpensive, simple to use, and easy to clean and store. Small areas (less than an acre) can be treated by a single person in a relatively short period of time. However, calibration of small unpowered devices can be difficult, and larger-capacity liquid tank sprayers may be difficult for physically smaller technicians to handle.

Powered Equipment

For large-scale pesticide applications, powered equipment is essential. This type of equipment ordinarily is mounted permanently in terrestrial or aquatic vehicles, or is attached to fixed- or rotary-wing aircraft. On the other hand, not all powered equipment is large. Some backpack sprayers may use small 2-cycle engines as a power source, and some of these miniature units have been used for ULV applications.

All power equipment works by pumping or blowing product from a storage tank through a distribution line or hose to various types of control mechanisms. The control mechanisms may be mounted on various devices such as guns, booms, or cylinders that can be aimed. For liquid products, the pesticide is applied through nozzles which control the shape of the spray pattern, the rate of flow of the spray, and the size of individual spray droplets. Nozzles are available in many sizes and configurations. Solid pesticides are spread using hoppers or air streams to propel the particles.

The details of the equipment are matched to the needs of the job and vary from machines designed to shoot pellets long distances to ULV machines designed to create tiny droplets to drift on the wind.

TYPES OF POWER APPLICATORS

There is a variety of powered application equipment used in vector control, including tank sprayers, mist blowers, granular applicators, and ULV sprayers. Vehicles used with power applicators have become highly specialized, and are often equipped with complex computerized tracking devices that produce maps of areas treated and records of vehicle speed, wind velocity, temperature, and pesticide application rates.

Foggers And Aerosol Generators

These types of devices work by breaking pesticide formulations into very small droplets. The output is may be visible as a cloud or a fog. The pesticide cloud is produced in one of two ways. In thermal fogging, the fog is produced by some type of heating element called a thermal generator. Here the pesticide is carried on heated oil particles. In cold fogging droplets are produced by atomizing nozzles, spinning disks, or high pressure. This form of fogging is much less visible. Large truck-mounted foggers have been used almost exclusively for control of flying insects such as mosquitoes and gnats. Small portable foggers have been used for control of roaches and stored product insects in warehouses and similar structures.

Fig. 8.1 A thermal fogger (Curtis Dyna-Fog, Ltd.)

Low Pressure Tank and Boom Sprayers

Low pressure sprayers deliver a low volume (0.5–40 gallons per acre) of dilute spray through nozzles with 30-60 pounds per square inch (psi) pressure. Tank and boom sprayers are designed to apply either undiluted (neat) or mixed product from a supply tank, through a single hose or a series of hoses through one or more nozzles. For vector control, this type of sprayer is usually mounted to an all terrain vehicle (ATV), an amphibious vehicle, or a low-speed aircraft to treat pastures. The purpose of the booms is to achieve wider and more even coverage for each pass of the vehicle carrying the sprayer.

This type sprayer comes in a variety of sizes, from small units with 10 or 15 gallon tanks mounted on ATVs to large units with water capacities of 1,000 gallons or more mounted on large flatbed trucks with a series of nozzles designed for roadside weed spraying.

Although boom sprayers are used in vector control, specific distribution is more important than uniform application of larvicides, so single-nozzle hand-gun type sprayers are used more frequently than boom sprayers.

Larval mosquito control products such as the liquid formulations of microbial insecticides, Bti and Bs, Golden Bear oil (GB-1111) and some herbicides are most commonly applied using this type equipment. For most of these products, adequate agitation is not a significant problem. For wettable powder formulations a mechanical agitator may be required.

Low pressure boom sprayers are relatively inexpensive. They are light in weight, have enough capacity to cover large areas, and may be adapted to many uses. However, low pressure boom sprayers are not useful when high volume is required because their rate of application is low. They cannot penetrate dense foliage because they operate at low pressure. They produce visible fogs, which some people find objectionable.

High Pressure Sprayers

Rarely used in vector control operations, high pressure sprayers are often called "hydraulic sprayers". This type sprayer is designed to apply large volumes (40 gallons per acre or more) of liquid at high pressure.

High pressure sprayers are more versatile than low pressure units. They can deliver very large volumes at pressures high enough to penetrate dense foliage or reach the tops of tall trees. They are usually well built, often have mechanical agitation, and are designed to resist wear. High pressure sprayers are also expensive. They are heavy and they require large amounts of water and fuel. Because the spray is produced at high pressures, there is a tendency for it to form small droplets subject to drift.

Air Blast Sprayers

This type sprayer is rarely used for vector control, but may occasionally used for fly control. These units use a high speed, fan-driven air stream to disperse the spray. A series of nozzles inject the spray into the air stream which breaks up the droplets and blows them onto the target. They can deliver either high or low volumes of spray.

The air blast sprayers give good coverage and penetration. They use low pump pressures and have mechanical agitation. They can be operated at low volumes and therefore require small amounts of water. The disadvantages of air blast sprayers are that they may produce small droplets that may create a drift hazard. Because of this they must be used under calm weather conditions. Typically these are relatively large, heavy machines that are not appropriate for use in small areas.

Low Volume Air Sprayers (Mist Blowers)

Mist blowers are a type of low volume sprayer used to control both larval and adult populations of mosquitoes. Mist blowers are characterized by relatively low fluid pressures, with flow rates of several ounces per minute. Dispersal of liquid insecticides is done using high air velocity. Typically, the product is run through hoses to a metering device which may or may not be connected to a conventional nozzle. Some large mist blowers are mounted on trucks and dispense mists of pesticide though nozzles mounted within large open cylinders. The cylinders can be aimed, sometimes by remote control, thus permitting aiming of the spray.

Fig. 8.2 A high pressure mist and dust sprayer (Buffalo Turbine Corporation)

Backpack-sized units can be used to treat areas up to several acres quickly and efficiently. The main advantage over air-blast sprayers is the lower volume of water needed. Mist blowers are particularly useful in mosquito control for treating dairy lagoons, roadside sources, and for applying a residual adult control product to individual properties. Small units are highly portable. Larger units can be mounted on pickup trucks or small trailers. A large mist blower can be used to treat many acres in a single day. Backpack-type power mist blowers allow rapid treatment of up to several acres by individual vector control technicians. Although this type of unit is best suited for liquid applications, some manufacturers offer the option of equipping them with hoppers for us with dusts and pellets or granules. Large units are unusable in areas without roads. Many large units also require two people for operation – one to operate the sprayer while the other drives the vehicle.

Ultra Low Volume Sprayers (ULV)

Ultra Low Volume (ULV) sprayers (i.e., cold fogging) are designed to apply extremely low volumes of highly concentrated pesticides in the form of very small (5-30 micron) droplets into the air. A micron, abbreviated "Ám", is equal to 1/25,000 of an inch. ULV sprayers are used primarily against adult mosquitoes, and require the use of insecticides formulated for this purpose. These formulations are either sprayed as ready to use without additional dilution or diluted with light oils. Most ULV sprayers utilize a small electric pump that can be very finely adjusted to vary droplet size and flow rate. Many commercial ULV formulations are available for adult mosquito control. A typical formulation contains a small concentration of pyrethrin (5-10%) combined with a synergist such as PBO. The remainder of the pesticide usually consists of an oil of some kind. With the exception of malathion, ULV products have a low percentage of active ingredient. ULV sprayers may be mounted in trucks, amphibious vehicles, or in aircraft. They are currently the most widely used type of sprayer for adult mosquito control.

Fig. 8.3. A ULV pesticide sprayer (Curtis Dyna-Fog, Ltd.)

ULV spraying is a highly effective means of adult mosquito control and a sensible alternative to the old fashioned thermal fogging machines. The combination of extremely low volumes (often less than one ounce of total liquid volume per acre) and pesticides having very low toxicity for humans and other vertebrates makes them very safe for both humans and other non-target organisms.

Effective ULV spraying requires careful attention to weather conditions. The very small droplets of concentrated pesticide tend to drift out of the target zone at high wind speeds, and generally, the higher the wind speed during application, the lower the effective swath. ULV applications are generally not effective for mosquito control at wind speeds over 10 MPH. Temperature is another important consideration because of the effect it can have on evaporation of the pesticide. The pesticide label should be consulted for specific meteorological limitations

Temperature inversions occur when temperatures at ground level are lower than temperatures at higher altitudes. This is the reverse of the normal temperature situation near the surface of the earth. During inversions, cold air is trapped by the warm air above it, and there is little vertical mixing of air. Under these conditions, the very small droplets produced by ULV sprayers remain suspended in the cool air within several feet of ground level. For some agricultural applications, and for application of herbicides, spraying under these conditions is considered undesirable because the spray droplets may remain suspended in the cooler air at ground level and damage non-target organisms. However, a temperature inversion is considered desirable for ULV mosquito control applications, because at the time of spraying female mosquitoes are host seeking (seeking a blood meal) near ground level, and the risk of damage to non-target organisms is low. If there is no lateral air movement, and no temperature inversion, the very small droplets will rise with vertical air currents above the level where they will effectively kill ground-level mosquitoes.

Because of the effect of weather variation on ULV applications, calibration should be checked frequently for flow rate and droplet size. Many new labels if not all require an annual calibration certification.

Solid Pesticide Applicators

Dusters

Equipment for dispersing dusts can be obtained in a variety of configurations, both powered and unpowered. Some equipment used for application of liquid pesticides can be used for solid materials with the installation of accessory hoppers and other devices.

Fig. 8.4 A Maruyama powered backpack sprayer for misting or dusting (Clarke Mosquito Control)

Granular Pesticide Spreaders

These devices are designed to apply coarse, dry uniform size particles to soil or water. The two major types are granular blowers (backpack or truck mounted) and seed or fertilizer spreaders mounted on some piece of equipment.

Granular spreaders eliminate the necessity of mixing the formulation with a solvent. The equipment is relatively inexpensive, and there is little drift hazard. The granules themselves are less hazardous to the applicator. Existing equipment (such as seeders) can often be modified to spread granules.

Power granular applicators allow vector control technicians to treat habitats where liquid products may not be effective, and allow a single technician to treat many acres in a day. Power backpack granular blowers are particularly effective in treating areas that are difficult to reach.

It may be difficult to calibrate power granular applicators because of the difficulty in maintaining constant travel speed while walking or driving. For units mounted on terrestrial vehicles or on backpacks, the equipment must be re-calibrated for each different product or formulation.

SPRAYER COMPONENTS

Tanks

Most sprayers have a single tank that holds mixed pesticide ready to be applied. For some larger truck-mounted sprayers, there are separate tanks for product and clean water, with a much smaller mixed (injection) tank of mixed product.

Some tanks may contain an agitation device, especially those designed to work with insoluble pesticide formulations such as wettable powders. Tanks are typically made of impermeable plastic, or stainless steel.

Tanks should be designed for easy filling and cleaning. It is a requirement that filler caps be lockable. Further, all tanks are required to be fitted with a device that maintains an air gap to prevent back flow from the tank into a water supply. As an alternative, the fill hose can be equipped with an automatic back pressure shut-off device. The tank is also required by regulation to have an easy-to-read accurate sight gauge or other external means of determining the internal level.

The opening of the tank should be fitted with a cover that can be secured enough to prevent spills or splashes. The drain should open through the bottom of the tank so that the tank can be emptied completely. If the tank contains a pesticide, it must have a label including the EPA registration number of the pesticide, the owner of the equipment, and any applicable precautionary statements

Agitators

Very few products used for vector control require continuous agitation inside a spray tank. In-tank agitation may be accomplished by hydraulic or mechanical means. Hydraulic agitation is achieved by pumping some of the solution back through the tank. Mechanical systems achieve agitation through the use of some sort of paddle or propeller mounted on a shaft in the spray tank.

Pumps

The pump is the heart of the sprayer. Most equipment used by vector control agencies are purchased as a unit, with a pump already installed. Choosing the correct pump requires matching it to the spray equipment to be used, and due consideration must be given to capacity, pressure, and resistance to corrosion and wear.

Gasoline engine-driven pumps have been supplanted by electric pumps in many modern spray systems, especially those using ULV spray techniques. Electric pumps are used in all new ULV mosquito control equipment, because these pumps are capable of the fine control over pressure and flow rate needed to meet label requirements for application rates. For other sprayers, there are many types of pumps available.


Nozzles

The nozzle is probably the most critical element in a system for application of liquid pesticides. The nozzle determines many spray characteristics. Nozzles affect the application rate, discharge shape (i.e., fine mist, cone, fan, etc.), droplet size, uniformity, pressure, and carry distance of the pesticide stream used for pesticide applications. Poor nozzle performance can destroy the effective and efficient performance of the entire sprayer system. The position of the nozzle on the aircraft may also affect the product output. The differential airflow created by an aircraft may affect uniformity of applications. For nozzles to perform efficiently, they must be cleaned, repaired, and adjusted frequently. Damaged nozzles should be replaced with new ones promptly.

For any given pesticide application and any given spraying system, various characteristics of nozzles must be considered for nozzle selection and installation:

l      Nozzle type

l      Nozzle size

l      Nozzle condition

For boom sprayers the following also may be important in achieving maximum effectiveness:

l      Nozzle orientation

l      Nozzle spacing on the boom

l      Boom and nozzle elevation above the ground

Types of Sprayer Nozzles

Many different types of nozzle are available commercially. Although not all of the following types are used in vector control operations, they are listed to provide an understanding of how nozzle characteristics can affect spray applications.

Flat Fan

This nozzle is used primarily on boom sprayers. It produces a nearly flat fan of spray in several selected angles and deposits an oval pattern on the ground. Less material is deposited at the outer edges, which requires the fan patterns to be overlapped to produce uniform coverage. This coverage depends upon proper spacing of the nozzles on the boom. When used from trucks or tractors, distance above the ground also has an effect on uniformity of application. These nozzles are used for broadcast or boom spraying in weed control work, and also in unpowered tank sprayers for work in home and garden situations.

Even Flat Fan

This nozzle also is used primarily on boom sprayers. It fills the outer portions of the spray pattern to produce even coverage across the entire width of the pattern. It is not designed for overlapping use on a boom. It is efficient for coverage of a given strip through the field as over a crop row. It is generally best for band spraying of herbicides in row crop work.

Cone

These nozzles are found commonly on unpowered backpack sprayers, unpowered tank sprayers, and boom sprayers. Spray is produced as either solid or hollow cone patterns. The cone angle contributes to better coverage of foliage and is one of the most popular nozzles for insect and disease control work.

Hollow cones are used primarily on unpowered backpack sprayers. They are designed for moderate to high pressures and are used where thorough coverage of crop foliage and uniform distribution is desired. There is little or no spray in the center of the pattern.

Solid cones are used for hand spraying, spot spraying, and moderate pressure foliar applications. The spray is well distributed throughout the pattern.

Flooding Or Impact

These nozzles are rarely seen in vector control use except for weed control applications. They have agricultural uses on farms and in home gardens, where they are used to spray liquid fertilizer solutions. They normally operate at low pressures with large droplets and can cover a wide area, so that it may by unnecessary to use a boom. This is an advantage on rough terrain or where many obstacles would hinder boom operation.

Offset

These nozzles lack the uniformity of the flat fan but can provide reasonably uniform coverage over wide areas for roadside and ditch bank weed control.

Atomizing

Atomizing nozzles produce a fine mist from liquid pesticides, and are the nozzles most frequently used in all types of ULV applications, both in ground and aerial spray operations. In comparison to nozzles used in compression sprayers, atomization nozzles can be very complex. Atomization is achieved in a variety of ways, depending upon the equipment used. In some the atomization is accomplished by rotation of the nozzle by electric motors, and others use wind-driven fans to produce rotation in the nozzle mechanisms.

Broadcast

These nozzles are used primarily from vehicles treating roadsides or rights of way with herbicides. They can be used either on boomless or boom-type sprayers. In the latter case a boom is used to extend the effective swath. The spray itself is in a wide flat fan pattern.

Solid Stream

In vector control, these nozzles are most often seen with handguns, hand can sprayers, and non-powered backpack sprayers when it is necessary to treat sites located at some distance from the operator. For larval mosquito control operations, best distribution of product is obtained by spraying upward and allowing the droplets to fall down onto the area. When compared to cone or solid cone nozzles, this application method allows much more rapid and efficient treatment of larger areas.

Adjustable

Adjustable nozzles are used frequently for vector control applications, and allow varying the spray pattern from a pinpoint stream to a cone. This type of nozzle is also used in small home garden sprayers. This type of nozzle is particularly useful when treating variable terrain. For example: The pinpoint stream nozzle may be used for a mosquito larval control application to target open areas in tulles or cattails in a pond, with the cone being used to treat flooded hoof prints along the edge.

Nozzle Construction And Use

Nozzles are subject to wear; they must be replaced before excessive wear occurs or they will fail to deliver the accurate amount and pattern of spray. The rate at which a nozzle wears depends upon several factors including: (a) the formulation of the material sprayed, (b) the nozzle design, and (c) the material used to construct the nozzle.

Characteristics of nozzle materials

l      Brass: Inexpensive, but wears quickly from abrasion. Good for limited use.

l      Stainless steel: Corrosion and abrasion resistant and relatively expensive.

l      Plastic: Very inexpensive. Resist corrosion, but swell when exposed to some solvents. Not recommended for high pressure spray applications.

l      Tungsten carbide and ceramic: Expensive, but provide long service. Highly resistant to abrasion and corrosion. Recommended for high pressure applications.

Selection, use, and maintenance of nozzles

l      Select nozzles that will provide the desired droplet size, volume of flow, and spray pattern.

l      After installation of new or repaired nozzles, properly calibrate the spray system to ensure proper application rates.

l      Avoid spraying tank mixes of pesticides containing hard particulate matter such as sand or metal particles. This greatly accelerates nozzle wear, even with expensive nozzles.

l      Always operate nozzles at the recommended pressure.

l      Mount the nozzles securely so that their location, relative to the target, is maintained constantly and properly.

l      Maintain nozzles in peak condition by periodic inspections, adjustments, and cleaning.

l      Never use a pocket knife or other metal object to clean a nozzle. It will damage the precision-finished nozzle edges and ruin the nozzle performance. A round wooden toothpick is much better. Better still, remove the nozzle tip and back-flush it with air or water first before trying anything else.

l      Don't blow through a nozzle by mouth, especially if it has been used for pesticide applications!

Sprayer Maintenance

Most troubles with sprayers can be traced to foreign matter that clogs screens and nozzles and sometimes wears out pumps and nozzles. Pump deterioration is brought about by ordinary use but is accelerated by misuse. The following suggestions will help prolong the useful life of pumps and sprayers.

1.      Use clean water. Use water that looks clean enough to drink. A small amount of silt or sand can rapidly wear pumps and other parts of the sprayer system. Water pumped directly from a well is best. Water pumped from ponds or stock tanks should be filtered before filling the tank. To avoid contamination of water supplies, regulations require that all application equipment be equipped with an air-gap separation or back-flow prevention device to prevent pesticides from being siphoned back into the water source.

2.      Keep screens in place. A sprayer system usually has screens in three places: a coarse screen on the suction hose; a medium screen between the pump and the boom or hose; and a fine screen in the nozzle. The nozzle screen should be fine enough to filter particles which will plug the tip orifice.

3.      Use chemicals that the sprayer and pump were designed to use. For example, liquid fertilizers are corrosive to copper, bronze, ordinary steel, and galvanized surfaces. If the pump is made from one of these materials, it may be ruined by a single application of the liquid fertilizer.

4.      Never use a metal object to clean nozzles. To clean nozzles, put on rubber gloves and then remove the tips and screens and clean them in water or a detergent solution using a soft brush. The orifice in a nozzle tip is a precision-machined opening. Cleaning with a pin, knife, or other metallic object can adversely change the spray pattern and capacity of the tip. If no brush is available, use a round wooden toothpick.

5.      Flush sprayers before using them. New sprayers may contain metallic chips and dirt from the manufacturing process. Sprayers which have been idle for a while may contain bits of rust and dirt. Put on rubber gloves and then remove the nozzles and flush the sprayer with clean water. Clean all screens and nozzles thoroughly before using the sprayer.

6.      Clean sprayer thoroughly after use. After use, flush the sprayer with water or flushing solution to clear lines and nozzles to prevent corrosion and material drying in the system. Be sure to wear appropriate personal protective equipment during clean-up procedures.

Be sure to discharge cleaning water where it will not contaminate water supplies, streams, crops, or other plants and where puddles will not be accessible to children, pets, livestock, or wildlife. The best way to use cleaning water is as a diluent in a sprayer tank for application of the same pesticide that was used in the sprayer before cleaning.

Additional Parts Of The Spray System

Each part of any sprayer must be working properly for the system to work efficiently. You should rely on your own judgment and the advice of experts such as pesticide dealers or sprayer manufacturers for details on the selection, maintenance, repair, and replacement of hoses, screens, filters, valves, gauges, and regulators, as well as for tanks, pumps and agitators.


CALIBRATion of pesticide equipment

Why Calibrate?

All pesticide labels contain information on allowable application rates. For a pesticide applicator to determine what dose is being applied, the application equipment must first be calibrated. There are many things that determine pesticide application rates. Some are related to the proper preparation of the tank mix, but many others are related to the operation and condition of the application equipment. Although power sprayers may produce consistent results when new, gradual wear of nozzles, pumps, and other components of the system will affect application rates. Further, no two pieces of equipment will behave in exactly the same way. For this reason, every time a vector control technician applies a pesticide, steps must be taken to ensure that the appropriate amount of pesticide is applied. Calibration of equipment is the means by which this is achieved.

Calibration of pesticide spray equipment is a legal requirement. It is a violation of state and federal regulations to apply a pesticide in any manner other than as specified on the label. Calibration of equipment is important to the success or failure of a pesticide treatment. It is a waste of time and money to apply any pesticide in an inefficient or ineffective manner.

What Is Calibration?

Calibration is the preparation of pesticide application equipment to ensure that a pesticide is applied appropriately, in the desired area, and with the correct amount of active ingredient. Calibration is the only accurate way to determine that the rate of application is consistent with the label requirements. Careful preparation of tank mix and proper operation of equipment during actual applications are also important factors to an effective and legal treatment.

Inaccurate pesticide application rates, spray patterns, and droplet size can all lead to ineffective and often illegal pesticide applications. These factors can lead not only to ineffective treatments, but also significant movement from pesticides away from the target area. Studies have shown that three factors stand out in pesticide applications that do not conform to label requirements: inaccurate preparation of tank mixes, worn spray nozzles, and improper calibration of spray equipment.

It is easiest to discuss calibration methods in connection with liquid forms of pesticides. However, dispersal of solid forms such as pellets or dusts follow the same principles, but with much different equipment and calibration procedures. These procedures will be covered toward the end of this chapter.

Principles of Calibration

Information Needed

l      The legal application rate as specified on the pesticide label

l      Amount of liquid applied by the sprayer per unit of area at a given speed and pump pressure

l      The amount of active ingredient contained per unit of liquid in the spray tank

l      The capacity of the spray tank

l      Assumptions For Calibration

l      The nozzles are in good repair, are of the proper type, and are made of the proper material

l      Nozzle pressure, pattern, and flow rate will remain constant during calibration

l      Speed of movement of sprayer (whether vehicle mounted or carried by technician) will be maintained constant during calibration

General Procedures For Calibration

Determining the Sprayer Output and Nozzle Output

There are various approaches to pesticide equipment calibration. Regardless of the approach used, the end result must always be a determination of the application rate, spray characteristics, and other specifications of the spray required by the pesticide label. An approach used for many types of ground and aerial applications using multiple nozzles mounted on a boom would include the following steps:

1.      Read the pesticide label and record the allowable and recommended pesticide application rate.

2.      Use water or appropriate diluent for pesticide to be applied for calibration.

3.      Adjust nozzles to desired patterns and record nozzle pressures when operating.

4.      Adjust speed of vehicle and record either MPH or engine RPM and transmission gear used.

5.      Fill the spray tank with water.

6.      Make trial runs spraying water at speed and pressure selected over one acre, or some fraction of an acre. When done, determine amount of water sprayed and calculate sprayer output in gallons per acre.

7.      While still operating the sprayer at a selected pressure, catch and measure output for each nozzle for 1 minute, then calculate an average nozzle output in gallons per minute.

8.      Count the number of nozzles to be used and measure the distance in inches between the nozzles on the boom.

9.      From the sprayer output in gallons per acre, the average speed of the trial run in MPH, and the nozzle spacing in inches, calculate a value for gallons per minute per nozzle based on the following formula:

Gallons per minute per nozzle = gallons per acre x MPH x nozzle spacing/5,940

10.  Check the value you get from the calculation against the flow rate you determined from catching and measuring the output from the nozzles. If the two values are far apart (more than 10%), re-check your calculations. Another cause for a large difference might be an error in the test to determine the sprayer output in gallons per acre.

11.  You also can perform this calibration in reverse, i.e., first determining average nozzle flow rate, then calculating sprayer output in gallons per acre using this formula:

Gallons per acre = (5,940 x gallons per minute per nozzle)/(MPH x nozzle spacing)

Remember that these values will be valid for only that speed, at that pressure, and at that nozzle output.

Some pesticide labels contain tables of values for calibrating spray equipment at various dilutions, application rates, and equipment speeds. If this is the case, calibration becomes much easier, and usually involves only checking the flow rates for individual nozzles. Unfortunately, not all labels contain this information, and the pesticide technician must do all the testing and calculations.

 

Calculation of the Tank Mix

Once you have calibrated the spray unit using plain water you will know how much spray the unit puts out per acre treated. From this you can figure out pesticide to add to the tank. To do this accurately, you will need to know:

l      The application rate called for on the pesticide formulation label. Typically, this will stated as pounds per acre.

l      The percentage of active ingredient in the commercial formulation.

l      The capacity of the spray unit tank.

l      The output of liquid (water) of the sprayer from the results of calibration

l      The amount of tank mix desired, if less than a full thankful of pesticide.

From this information the amount of pesticide formulation needed for a full or partial tank of tank mix can be determined. An important consideration in doing this will be reconciling the units used for application rate of active ingredient (ai) specified on the label (usually by weight of ai) with the units used for sprayer output (usually liquid volume). For pesticide formulations that are mixed with water, the following formula can be used:

(Gallons of spray wanted) x (percent of active ingredient wanted) x 8.3/percent active ingredient in insecticide formulation

The figure 8.3 appears in the formula because this is the weight of a gallon of water in pounds based on a specific gravity of 1.00. Oils have lower specific gravities, and this must be taken into account if oils are used as a diluent. This information is usually contained on the label.

There are many variables involved in this process, and the calculations will depend upon the diluent used (if any), the size of the area to be sprayed, the type of equipment used, and other factors. Rather than furnish specific details to every situation a pesticide technician will face, several examples will be provided. Appendix 3 contains conversions for various units of measure and mathematical formulas used in pesticide equipment calibration. This information may be useful for calibrating equipment based on manuals written with metric units.

Calibration of Equipment for Typical Vector Control Operations

Applications Of Solid Pesticides

The principles of calibration are the same for applications of pellets, powders, and dusts, but the equipment will be different from that used for liquids. Some of this equipment will be large devices mounted on trucks or airplanes, and some will be hand-carried and powered. Both powered and unpowered devices use hoppers to hold the pesticide, and an impeller of some kind to discharge the material in a uniform manner. Discharge is controlled by a valve of some kind in both powered and unpowered units.

Instead of water, calibration can be with blank (inert) granules or other solids. This type of calibration will be on the basis of weight, so you can place a given weight of solid material in the hopper and measure the amount of material discharged on the basis of weight per unit of time and weight per unit of area.

Differences in speed between vehicle-mounted and human-carried equipment will be the same as for liquid sprayers, and the same methods of accounting for speed apply.

Although calibration is a legal requirement for all pesticide sprayers, there will be times when it is impossible to apply product in a consistent manner. One method of ensuring the appropriate application rate is to measure or estimate the area to be treated, and mix or load only enough product to treat the area appropriately. Begin by treating the area more rapidly than usual, ensuring that the area is completely covered. Then with any remaining product go back over the same area. If this method is used it is important that applicators avoid overexposing themselves to the pesticide.

Applications From Powered Knapsack Sprayers

This type of calibration will be similar to the general example given, except that movement speed will be more difficult to control, the areas sprayed will be smaller, and a single nozzle will almost always be used.

To determine the sprayer output rate, you would lay out an area representing an even fraction of an acre. A rectangle measuring 100 x 109 feet would be one-quarter of an acre. You can count the amount of water used to spray the plot, multiply by 4, and calculate the output in gallons per acre. You should also note the time in minutes it takes to spray the plot. From this you can calculate the gallons per minute of spray based on your walking pace. To check the calculation and the flow rate of the nozzle, you can catch and measure the output for one minute and record the result as gallons per minute. This should agree with your earlier value from walking the test plot.

Again, the calibration values will apply only for the nozzle used and the walking pace of application. The determination of amount of pesticide needed will be done as before, and will depend on the percentage of active ingredient in the commercial formulation, and the type of diluent (if any) used.

Applications From Unpowered Compression Sprayers

This type of sprayer is used frequently for treatments of small terrestrial or aquatic sites for various kinds of pests, such as treatment of small ditches for control of mosquito larvae. Calibration of hand-carried and hand-pumped presents special challenges. Flow rate varies with pressure, and pressure varies widely with these kinds of devices. Some have pressure gauges, others do not. Also, since the travel speed of the sprayer will be the travel speed of the human carrying the sprayer, maintaining constant speed is difficult. Again, the end result of calibration is the same: to make sure the application conforms to the pesticide label requirements.

An approach that should provide a reasonable estimate for application rate will be similar to the methods used for the powered backpack sprayer. Measure a small plot that represents some even fraction of an acre (a plot 50 x 55 feet would be about 1/16 of an acre) and measure the time and number of gallons it takes to spray the plot. While spraying, walk in a manner that would be the same as you would walk making a real treatment, and keep the tank pumped up in a routine consistent with the actual application.

Calculate values based on gallons per minute and gallons per acre as before. Doing the trial spray several times will provide you an opportunity to check the consistency of your applications.

When doing the actual applications it will be necessary to estimate the size of your target area. In difficult areas where the spraying will be intermittent, you may have to keep track of the time spent while actually spraying with a stop watch.

ULV Applications From Air Or Ground-Based Sprayers

Calibration for applications using ULV methods is more complicated than most other types because sprayers must be calibrated for both flow rate and droplet size.

Flow Rate

Flow rate should be checked after all nozzles are inspected for damage and completely cleaned. One or more nozzles should be checked with the pump operating at the appropriate pressure. All lines and screens should also be checked for obstructions to make sure insecticide will be free-flowing. If a battery-powered electric pump is used, the battery should be first checked to make sure it is fully charged.

The flow rate of the nozzles can be controlled at the pump with most equipment by adjusting a knob or screw at the pump. To measure flow rate, either water or mineral oil should be collected in a graduated cylinder for a set period of time. This should be repeated several times and an average value determined for each nozzle. Finally, and average value for all of the nozzles are determined and recorded.

Droplet Size

The range of droplets produced using ULV equipment is characterized by a measurement called volume median diameter (VMD). Labels for pesticide formulations designed for ULV applications will contain information on the required range of VMD values for both ground and aerial application. As an example, the label for Clarke Biomist® 31+66 ULV specifies that for ground applications, the VMD of droplets must fall with a range of 8 to 30 microns (Ám) and that 90% of the spray must contain droplets of less than 50 Ám. This sounds like an incredibly difficult measurement and calculation task for insecticide technicians, but modern analytical equipment is available that makes the measurements and provides complete profiles for the droplet spectrum. The DC-III (KLD Labs, Inc., Huntington Station, NY) uses what is known as a "hot wire" approach.

Other analytical units, such as the VisiSizer from Oxford Lasers perform the same functions, but with laser beams that result in digital images of the pesticide stream that are fed into a computer for complete analysis.

Fig. 8.5 The DC-III Analyzer (KLDLabs, Inc.)

Older manual methods involve waving a glass microscope slide by hand through the pesticide stream and then examining the slide under a microscope. Upscale approaches to this method use mechanical rotating devices instead of a human hand. In either case, the slides are examined under a microscope and the droplets then are measured and counted by hand.

If droplets are not within the desired range for the application, various adjustments must be made, depending upon the method being used to break up the pesticide into droplets. In many units, the droplets are produced in specialized nozzles that use streams of high pressure air to shear the droplets off the material as it enters the nozzle. To adjust the range of droplet sizes, the speed and volume of air moving past the nozzle are adjusted. Generally, the higher the speed and volume of air, the smaller will be the droplets.

For after-spray assessments, these and other methods, such as the use of dye cards placed in the path of the sprayer, are used to collect spray particles. These are then analyzed in the laboratory to determine if the proper droplet sizes were achieved in an application.

Frequency of Calibration

For ULV sprayers, flow rate should be checked regularly – depending on how often the machine is used. Droplet size should be tested at least annually prior to the spray season, and after any repairs to the machine. In the unusual event that the ULV spray nozzle itself is damaged, it must be professionally machined or replaced.

Operation of Spray Equipment After Calibration

Since consistent and uniform distribution of pesticide is necessary for successful applications it is necessary to operate spray equipment properly. This means keep vehicle speed as constant as possible. Remember that at a given pump pressure, if you reduce speed significantly you will increase pesticide application rate significantly. Anyone who has pushed a fertilizer spreader around a lawn knows what happens if you stop for a break and fail to close the hopper!

All modern power equipment includes pressure gauges for pumps. Most pressure gauges are located within easy view of the driver. Observe pressure readings frequently and make necessary adjustments to maintain constant pump pressure throughout the application.

If you see evidence that the application isnÝt going correctly (e.g., if pump pressure is fluctuating wildly) stop and check the equipment, and if necessary, re-calibrate.




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