Spraying Equipment

Chemicals to control insects and diseases that affect plants can be applied in a great variety of ways. These include broadcast sprays, directed or band sprays, in-furrow application, soil injection, spot treatment, dust and granular application and more. Some methods such as air blast spraying, fumigation, aerial application and chemigation are highly specialized and require special training to use the equipment associated with these application methods. Only methods that are in general use are presented here.

Hand Sprayers. Hand sprayers are ideally suited to apply small quantities of pesticides. They can be used to spot spray; to apply chemicals inside structures such as greenhouses or to treat areas that are hard to reach.

The compressed air sprayer is usually a hand-carried sprayer with a capacity of 4– 12 dm³. Pesticides and water are proportioned according to label instructions and placed in the airtight tank. Air pressure in the tank is increased with the built-in pump until spray is freely delivered when the control valve is opened (Fig. 1.251). This type of sprayer typically has a shoulder strap or hand grip for the operator. The nozzle and control valve are manipulated by the free hand and directed toward the target pest. As nozzle output begins to diminish, the air pressure must be recharged by operating the air pump. Most hand sprayers do not have a pressure regulator to maintain constant application pressure.

Figure 1.251. Compressed air sprayer.

Figure 1.252. Controlled droplet applicator

Battery-operated Hand Sprayer. Battery-powered controlled droplet applicators (CDA) use a spinning disk type of atomizer to produce a uniform droplet size. These units are suitable to apply concentrates and ultra low volume (ULV). Thus the amount of material that must be carried by the operator is greatly reduced. The droplet size is inversely proportional to the disk RPM. Higher RPM reduces the droplet diameter. The units are lightweight, easy to use and usually powered with common flashlight dry cells; the batteries being positioned in the handle (Fig. 1.252). These sprayers are limited to treating small areas and their cost, battery expense and low work capacity may restrict their use.

Small Motorized Sprayers. Some small sprayers have all the components of large sprayers but are mounted on a small cart or wheelbarrow. Tanks are usually 60–120 dm³ capacity. Typically they are propelled manually or pulled by a small tractor. A small engine, 3–4 kW, provides power for the pump and agitation system. This greatly increases their capacity over hand-operated sprayers, but their small size still makes them unsuitable for general field use. Most models have an adjustable nozzle on a hand gun; others may include a small boom with multiple nozzles.

Boom Sprayers. These sprayers usually are low pressure units and are the principal type used for field spraying. Fig. 1.253. Tanks and booms may be mounted on tractors or trucks, designed as trailered units, powered and pulled by a tractor, or even self-propelled. The pumps are usually roller, centrifugal or diaphragm pumps. Tank capacity may range from 200–4000 dm3. Booms may range in length from 8–36 m. Boom height must be easily adjustable from 30–180 cm above the target to insure good nozzle performance and spray pattern overlap. Some booms are self-leveling to reduce travel undulation and provide more uniform application.

Figure 1.253. Typical boom sprayer—3 point mounted.

Tandem axle wheel arrangements or large diameter wheels also are used to smooth out travel and improve application uniformity over rough ground. Booms are sometimes referred to as wet, where spray fluid is carried to the nozzle inside the boom structural members, or dry, with the spray material carried to the nozzles by connecting hoses. The spacing of the nozzle on the boom may range from 20–150 cm depending upon the type of nozzle and its application.

Boomless Sprayers. Boomless sprayers as a class cover a wide range of tank sizes, pressures and delivery rates. One type of boomless sprayer has a center cluster of nozzles, operates at low pressure and projects a wide swath pattern without being encumbered by a wide boom. Uniformity usually is not as good as with a boom sprayer, but is very acceptable for many field and roadside applications. Where spray must penetrate thick foliage or animal hair or reach the top of tall trees, high pressure is required. Piston pumps usually are used to deliver pressure from 1–3 MPa.

Application rates may range up to 240 dm³/min and are typically applied manually with a hand gun. Sprayers with tank capacities of 2000–4000 dm³ may be truck mounted, trailered or self-propelled units.

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