Chapter 25

Pesticide Application and Equipment in Greenhouses

Sprayer Components

Many pesticides used to control insects, disease, and weeds in the greenhouse are applied with hydraulic sprayers. All sprayers have several basic components: tank, pumps, filtration devices, fans, and nozzles.

Tanks

Tanks should be made of a corrosion-resistant material. Suitable materials used in sprayer tanks include stainless steel, polyethylene plastic, and fiberglass because of their rust and corrosion resistance. Stainless steel tanks are the most durable, corrosion-resistant, and the strongest option. Due to their high cost, they make the most sense for high-use spraying situations. Polyethylene plastic tanks are lighter weight than metal tanks yet quite durable and extremely corrosion-resistant. Improvements in plastic technology have reduced both stress cracking and damage from ultraviolet light (verify that UV inhibitors have been added to the plastic).

Agitation System

Many spray mixtures must be agitated (stirred up) to keep the pesticide and carrier mixed. For liquid concentrates, soluble powders, and emulsions, the system bypass line is usually adequate to keep the formulation well mixed.

Direct Injection Sprayers

Direct injection sprayers use separate tanks for the water and the pesticide. The pesticide is injected into the water stream at a rate dictated by the forward speed and controller. While more costly to purchase, injection sprayers have the advantage of reducing risk since you never mix more than needed.

Pumps

The pump must deliver the necessary flow to all nozzles at the desired pressure to ensure uniform distribution. When selecting a pump, consider the pressure ranges the pump can handle, the gallons per minute it can supply, its resistance to corrosive damage from pesticides, ease of priming, and power source availability. It’s a good idea to choose a slightly oversized pump. A pump must have sufficient capacity to operate a hydraulic agitation system, as well as supply the necessary volume to the nozzles. A pump should have a capacity of at least 25 percent greater than the largest volume required by the nozzles. This will allow for agitation and loss of capacity due to pump wear. The materials in the pump housing and seals should be resistant to chemicals, including organic solvents.

Piston Pumps

Piston pumps are among those most commonly used for applying agricultural chemicals. These are positive displacement pumps, where output is proportional to speed and independent of pressure. There are two types of piston pumps used for different application purposes: high pressure-low volume-high speed, and low pressure-high volume-low speed applications.

Diaphragm Pumps

Diaphragm pumps, although often more expensive than other pumps, have some important advantages in use and maintenance. These include: 1) a small number of moving parts; 2) a limited area of exposure of pump components to the injected chemicals; and 3) design which allows for easy adjustment of injection rate.

Centrifugal Pumps

Centrifugal pumps are the most popular type for low-pressure high-volume sprayers. They are durable, simply constructed, and can readily handle wettable powders and abrasive materials. Pumping action is created by a high-speed impeller that literally throws the materials out of the pump.

Roller Pumps

Roller pumps are widely used on low-pressure boom sprayers for herbicide application and run efficiently at low power take-off (PTO ) speeds. They are relatively inexpensive and adaptable to a wide range of pressures, volumes, materials, and situations.

Filtration Devices

Proper filtering of the spray mixture not only protects the working parts of the spray system but also avoids misapplication due to nozzle tip clogging. Three types of strainers commonly used on sprayers are tank filter strainers, line strainers, and nozzle strainers. As the mixture moves through the system, strainer openings should be progressively smaller. Tank filter strainers prevent large contaminants (grass, rocks, labels, etc.) from entering the tank upon filling. A second, more finely meshed filter is in the suction line to the pump. The last place to filter out contaminants is at the nozzle.

Fans

Fans are used to move spray into vines to enhance the uniformity of pesticide deposition on the plants. Air movement also displaces leaves and branches, which aids spray penetration and increases the exposure of surfaces to spray. The air stream helps to atomize the spray and assures spray droplet velocity, which increases impingement (sticking) of very small spray droplets to the plant canopy.

Other System Components

Nozzles

The nozzle regulates the flow rate, atomizes (breaks up) the mixture into droplets, and disperses the droplets in a specific pattern. Nozzle type and location also influence spray pattern. Nozzles usually have several components, including a body, cap, strainer, disc and core (orifice and whirl plate). Unfortunately, no one nozzle can cover every type of application. Nozzles vary according to capacity (gpm or gph), spray pattern angle, and shape of spray pattern. See Section 25.2, Nozzles for a more in depth explanation on nozzle materials, types, and droplet size classification.

Pressure Regulators

A pressure regulator is one of the most important parts of a sprayer. It controls the pressure and therefore the quantity of spray material delivered by the nozzles.

Pressure Guages

Pressure gauges monitors spray system operations because a sprayer is set up to operate within a specified pressure range.

Control Valves

Control valves should be located between the pressure regulator and the nozzles in order to regulate the flow to specific boom or manifold sections or even to individual nozzles.

Electronic Systems

New systems using electronics have been developed to improve pesticide application. These systems can monitor and guide the spray equipment in various ways. Some systems sense the travel speed and the total flow of spray to the boom.

Hoses, Clamps, and Fittings

All components that come in contact with the chemical mixtures should be constructed of materials that are resistant to chemicals and to sunlight degradation. The pressure rating of all components should be adequate to withstand all operating pressures. Hoses and fittings should be protected from mechanical damage.

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