Pesticide Application in Vineyards
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 a particular 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 are made from several materials. The most common are brass, nylon, stainless steel, hardened-stainless steel, tungsten carbide, thermoplastic, and ceramic. Ceramic and tungsten-carbide nozzles are very long-wearing and extremely corrosion-resistant.
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 proper selection of a nozzle type and size is essential for proper pesticide application. Spray nozzles fall into three basic categories:
Hydraulic nozzles operate on the principle of driving a liquid under pressure through an orifice considerably smaller than the diameter of the feed line.
Air-shear (Air-Assisted) Nozzles
Some air-blast sprayers use the high-speed air discharge to break up the spray liquid into droplets rather than orifice nozzles and pressure. Discharging the spray directly into the airstream against the air flow produces the smallest droplets; at 90 degrees to the air-stream, intermediate breakup; with the air flow, the least breakup and the largest droplets.
Controlled Droplet Applicators
Controlled droplet application is a term used to describe a new method of applying pesticides. Controlled droplet application (CDA) technology uses centrifugal force instead of hydraulic pressure to produce droplets and spray pattern. CDA produces spray droplets that are relatively uniform in size, which would normally drift. When used in conjunction with a tower and cross-flow fan design, the smaller droplets are actually directed into the canopy. On the other hand, conventional spray nozzles produce droplets that vary widely from small droplets that may drift or evaporate before reaching the target, to large droplets that concentrate too much of the pesticide in one spot.
Droplet Size Classification
Droplet-size information is useful for determining the correct nozzle for a pesticide application. A classification system developed by the British Crop Protection Council (BCPC) and the American Society of Agricultural and Biological Engineers (ASABE) assigns a droplet-size category to a nozzle based on droplet-size spectrum (See Table 25.2).
Pressure Effects and Nozzle Spray Angle
Spray droplet size can be changed by altering pressure. Spray droplets become coarser (larger) when pressure decreases and finer (smaller) when pressure increases. Spray angle is the angle formed between the edges of the spray pattern from a single nozzle.
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