Pesticide Application and Equipment in Greenhouses
Sprayer Components
Sprayers come in a large range of types and sizes, from small, hand-held sprayers to large, self-propelled machines. While there is such a large variety, there are some basic components that are found on nearly all types of sprayers. The basic components used in liquid application systems include tank, pumps, filtration devices, fans, and nozzles.
Tank
The spray tank should be of an appropriate size for the type of sprayer used and the volume of pesticide mixture required for the area to be sprayed. The shape of the tank should allow for easy access for filling and ease of drainage and cleaning.
Pump (liquid flow)
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.
Agitation System
Many chemical formulations consist of fine powders or particles that need to be held in suspension in the chemical mix. If the mix is left to stand, these particles may settle on the bottom of the tank. A system to agitate or mix the chemical is therefore required. This is usually achieved by recirculating some of the spray mix back to the spray tank.
Filtration System
Filters are required to prevent nozzle blockage. Blockage results in wasted time, increased risk of chemical exposure if nozzles or filters require cleaning in the field and poor coverage in the field if individual nozzle blockages are not detected. Factors such as the water source, pesticide formulation and pump agitation capability influence the type of filtration system required for the sprayer.
Pressure Regulators and Control Valves
Liquid flow rate and pressure to nozzles must be controlled to ensure that sprayer output is consistent. This is generally achieved by use of pressure regulators and/or control valves. These may be operated manually or electronically, particularly for the larger sprayers.
Fans
Fans are used to move spray into plants 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. There are three main types of fans: axial flow, centrifugal, and cross-flow.
Nozzles
The term “nozzle” is used in a wider sense of any device through which spray liquid is emitted, broken up into droplets and dispersed over the target. The nozzle regulates the flow rate, atomizes (breaks up) the mixture into droplets, and disperses the droplets in a specific pattern. Nozzle selection is one of the most important decisions to be made related to pesticide applications. The type of nozzle affects not only the amount of spray applied to an area, but also the uniformity of the applied spray, the coverage obtained on the sprayed surfaces, and the amount of drift. Each nozzle type has specific characteristics and capabilities and is designed for use under certain application conditions. Nozzles usually have several components, including a body, cap, strainer, disc and core (orifice and whirl plate). Nozzles vary according to capacity (gpm or gph), spray pattern angle, and shape of spray pattern. Unfortunately, no one nozzle can cover every type of application.
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