Courtesy of Larry Schulze, University of Nebraska professor; Nebraska Private Pesticide Applicator Self Study Manual; and Dr. Wayne G. Buhler, North Carolina State University Department of Horticultural Sciences

An operator sprays a tree with a Solo Sprayer Model 433 -- a high pressure sprayer with 20-gallon tank capacity. It reaches a controlled operating pressure of up to 25 bar, which achieves a fine spray mist even at extreme heights. At 30 bar, it can achieve a flow rate of three gallons per minute, using the push-pull piston pump.

The successful application of pesticides depends on use of appropriate equipment and its careful maintenance. The amount of pesticide applied, how efficiently it controls the pest species and the safety of its use to both the environment and applicator all depend on the equipment.

There is a wide variety of equipment available, each with advantages and limitations for the particular situation. It is important to choose the equipment best suited to the use.

 

Pattern check for a rotary spreader. Rotary spreaders cover a wider area faster and are preferred for larger areas. Steering errors also are less critical. Compared with drop spreaders, rotary spreaders are easier to push, have better ground clearance and are not as easily knocked out of calibration.

Sprayers – Tanks

Tanks used to apply pesticides should be constructed with materials that resist corrosion. Fiberglass and stainless steel resist corrosion caused by most chemicals, as do plastic coatings; however, durability of these materials is reduced if cracks or chips in the coating develop and expose the base metal to corrosive forces. Untreated metal can be used for applying non-corrosive pesticide solutions but precautions should be taken to prevent rust and scale. All tanks should be constructed to prevent leaking and rupture. Regardless of their construction, sprayer tanks should be of a design that allows for ease in inspection, filling and cleaning. A drain plug should be located at the bottom to permit complete drainage when cleaning.

Agitators

Sprayer systems should include adequate agitation in the sprayer tank to provide uniform mixing of the pesticide during application. Proper agitation is particularly important when wettable powder formulations are used or they will settle to the bottom.

There are various agitation systems: By-pass agitation involves pumping excess spray material back into the tank under pressure. This system is good for stirring solutions and emulsions, but may not adequately mix wettable powders. Mechanical agitation uses paddles or other devices to mechanically agitate the spray solution. Mechanical agitators provide excellent mixing but are expensive and difficult to maintain. Jet agitation uses liquids from the sprayer’s pressure system. The line to the agitator in this system should be connected between the pump and any cut-off valves so that agitation continues when spraying has stopped.

When using or calibrating a drop spreader be certain to walk at the desired speed before starting the flow of granules when crossing the starting point. At the finish point, stop the flow, but continue walking.

Pumps

Any pump used to apply pesticides must supply the spray volumes at the pressures required for application. The selection of a pump is usually influenced by cost and durability for the intended use.

Piston pumps are among those most commonly used for applying chemicals. These are positive displacement pumps that can be used for both corrosive and abrasive materials. The two types of piston pumps are for different application purposes: high pressure-low volume-high speed and low pressure-high volume-low speed applications.

Roller or roller impeller pumps are also used in many spray systems. These pumps are adaptable to a wide range of pressures, volumes, and materials. They are accurate in the amount of spray material applied because they maintain constant pressure and flow.

Centrifugal pumps are designed for use with abrasive and coarse materials. Pumping action is achieved by use of a high speed impeller that throws the material out of the pump. These pumps are used to spray high volumes, but the maximum spraying pressures are limited to 5,060 pounds per square inch (psi).

Gear pumps are semi-positive pumps that develop uniform, moderate pressures but output volume is limited. They cannot be used with abrasive materials.

Nozzles

Nozzles should be chosen to give the proper particle size, spray pattern and application rate for the pressures used during application. Each nozzle is rated as to the amount of fluid that will be applied at a specified pressure and ground speed. Nozzles also are rated by the angle at which the sprayed material is discharged.

Nozzles are generally classified as to the pattern of spray they deliver. The more common types of nozzles are: the flat spray nozzle produces a rather coarse spray in a fan-shaped pattern. Even coverage is achieved when spray areas overlap in boom sprayer applications. Flat-spray nozzles are suitable for most insect and weed control applications where penetration of the foliage is not necessary. A wide angle nozzle with a flat spray pattern can be operated close to the ground to minimize drift.

A garden application shows the sprayer powered by a piston pump with Viton??????oe seals providing up to 90 psi. The three-gallon sprayer can be used for larger applications. The lightweight design and low effort piston pump system ensure consistent pressure, effective patterns, high efficiency and reduced user fatigue.

Nozzle Construction

Nozzles are constructed from many different materials, each with different characteristics in terms of resistance to corrosion, abrasion or reaction with spray mixtures. Selection of nozzle types should be made by balancing the characteristics of the construction materials against the cost of the different nozzles.

Strainers

Strainers or screens are placed at various points in the sprayer system to exclude foreign material that would wear out precision parts or clog the system. Screens are normally placed at the entrance to the pump intake line, in the line from the pressure regulator to the boom and in each nozzle. Usually 25- to 50- mesh screens are used in the intake hose, 50- to 100- mesh screens in the boom supply and screens the size of the nozzle tip opening for the nozzle. For spraying wettable powders, all screens should be 50-mesh or coarser to prevent clogging.

Pressure Regulator

The pressure regulator, or relief valve, maintains regulator required pressure in the system. This is a spring loaded valve that opens to prevent excess pressure in the line and allows some of the solution to return to the tank. Most pressure regulators are adjustable to permit changes in the working pressure of the system.

Streaks in the pattern indicate problems with nozzle height, alignment or output. Adjust boom height or change nozzles until pattern is even.

Types of Sprayers

Low-pressure sprayers are normally designed to deliver low to moderate volumes at 15 to 80 psi. Application is usually made through a boom equipped with nozzles. Low-pressure sprayers are used primarily for weed and insect control where pressures of 80 psi provide sufficient crop coverage. Low-pressure sprayers are also used to apply liquid fertilizers or fertilizer-pesticide mixtures.

Low-pressure sprayers requiring low flow rates often are equipped with roller-impeller pumps. Centrifugal pumps are generally required where high flow rates are needed and when agitation of the spray mixture is required.

High-pressure sprayers are designed to deliver large volumes at high pressure. They are often similar to low-pressure sprayer systems but have a piston pump which can deliver high volume (up to 50 gallons/minute) at high pressure (up to 800 psi). Application rates of high-pressure systems are typically 200 to 600 gallons per acre. Sprays are usually applied with either a boom or a handgun. All components of a high pressure system must be designed and selected to withstand the high pressures. High pressure systems are used primarily on trees for insect and disease control. High pressure systems may also be designed for washing equipment.

Air-blast sprayers use a blast of air, instead of large volumes of water, to propel the spray mixture. Nozzles deliver the spray into a high-velocity airstream generated by a powerful fan which breaks the spray into fine droplets. Air-blast sprayers are typically used on fruit trees, shade trees and for fly or mosquito control.

Air-blast sprayers provide good coverage of foliage, are lighter weight, use lower pressures, and are easier to operate than high-pressure sprayers. However, they are often expensive and produce fine particle sprays which drift readily. Because of this drift potential, use of these sprayers is more limited by weather conditions. Since relatively low water volumes are used, calibration is particularly critical with air-blast sprayers.

Special air-blast sprayers which have higher air velocities (120 to 200 mph) and lower air volumes are known as mist blowers. These sprayers produce a fine spray.

Small-capacity sprayers are designed for spot treatments, home and garden pest control, small tree and nursery spraying and for restricted areas unsuitable for larger units.

Most are hand sprayers which use compressed air to pressurize the supply tank, forcing the air through a nozzle. Several types of small power sprayers are available that deliver one to three gallons per minute at pressures up to 300 psi; adjustable handguns are usually used with these units, but spray booms are available on some models. Small-capacity sprayers are relatively inexpensive, simple to operate and maneuver and easy to clean and store. Adequate agitation and screening for wettable powders, however, is necessary. Since there is a direct reliance on the operator for movement across the treated area, there can be substantial variability in application rates.

To spray uniformly, adjust flat fan nozzles so that 30 to 50 percent of the spray pattern overlaps. The middle sprayer covers a total of 30 feet across, with 10 feet of overlap to the right and left sprayers.

Pattern check for a rotary spreader

Place one box in the center with enough space on either side to allow the spreader wheels to pass through. Space the remaining boxes on 2-foot centers to either side of the center box, as shown in Figure 14. All boxes must be identical in size, typically 1 to 2 inches deep, with an area of at least 1 square foot. There should be an odd-number of boxes in the row covering 11/2 to 2 times the anticipated effective swath width. Place a piece of cloth in the bottom of each box to keep particles from bouncing out.

Pour some product into the rotary spreader and choose the setting recommended on the label. Make at least three passes over the boxes to obtain an accurate assessment of the distribution pattern. Be sure to operate in the same direction and position on every pass. Weigh the granules collected in each box and plot a distribution pattern, or pour the granules from each box into its own vial or small bottle. The vials must be identical in size and shape. When the vials are placed side by side in the same order as the collection boxes, a plot of the distribution pattern is visible, as shown in Ideally the contents of the vials form a bell-shaped curve that peaks in the center and descends evenly on each side. Determine which have one-half the amount of product in the center vial. The distance between these boxes is the effective swath width. Use this figure to space spreader passes.

For example, if the center vial has material that is 2 inches deep, and the vials from the 6-foot positions (6 feet left of the spreader centerline and 6 feet right of the spreader centerline) have material 1 inch deep, the effective swath width is 12 feet.

If it appears that the half rate falls between two boxes used in the test, take the mid-point between those boxes as half the effective swath width. For example, you estimate that the halfrate volume falls between boxes located 4 and 6 feet to the left and 4 and 6 feet to the right of center. The effective swath width is 10 feet (5 feet left and 5 feet right of the centerline).

If the two boxes used to determine effective swath width do not contain the same amount of product (nonsymmetrical pattern), adjust the spreader to correct the pattern. Follow the manufacturer?EUR??,,????'???s recommendation on pattern adjustment.

Certain models allow you to block off part of the metering port(s) or move the drop point of the granules on the impeller.

Checking the pattern over a paved area is a quicker, though less accurate, method to estimate the distribution pattern. Particle bounce and scatter make this method inexact, but it does reveal gross distribution errors. A rough estimate of the effective swath width can be made by measuring the central two-thirds of the total swath.