Pesticide Application in Vineyards
Spray Nozzles
Nozzle selection is one of the most crucial decisions to be made in relation 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.
Atomization
Atomization is the process of breaking a bulk liquid into a spray of tiny droplets or particles. This can be done in several ways, among them are: (1) hydraulic nozzles, (2) air-shear nozzles, and (3) rotary atomizers (controlled droplet applicators). Atomizers typically perform three functions: they regulate flow, create droplets from the liquid, and disperse those droplets into an initial pattern. Hydraulic nozzles create droplets by atomizing liquid at high pressure through a small orifice.
Hydraulic Nozzles
Hydraulic nozzles operate on the principle of driving a liquid under pressure through an orifice considerably smaller than the diameter of the feed line. The change from large to small diameter results in a significant increase in the liquid’s velocity, which in turn causes the stream of liquid exiting the nozzle to become unstable and to break up into small drops. Hydraulic nozzles consist of a body, cap, filter, and tip. Vineyard sprayers often use different-sized hydraulic nozzles at different locations on the manifold. Thus, the sprayer applies different amounts of spray to other parts of the vines. On all hydraulic nozzles, the pressure of the liquid at the orifice affects the flow rate, spray angle, and droplet size.
Air-Shear (Air-Assisted) Nozzles
Unlike hydraulic nozzles, which use liquid pressure to create droplets, air shear nozzles use air velocity to form droplets. Air-shear nozzles create optimally sized droplets, which remain unaffected by changes in speed and pressure, ensuring a uniform application over the entire vineyard. Air shear nozzles tend to provide finer atomization than hydraulic nozzles. A finer spray is needed to achieve good coverage, but losses can increase due to drift and evaporation. Due to the smaller controlled droplets and directed air blast, air-assisted nozzles enable highly efficient water use.
Controlled Droplet Applicators
Controlled droplet applicators (CDAs) do not rely on hydraulic pressure and orifice atomization (the principle behind hydraulic nozzles). Instead, CDAs use centrifugal force—usually a rotating disc, cage, or mesh—to control droplet size precisely, independent of liquid pressure. A CDA is a type of mechanical atomizing nozzle that produces uniform-sized spray droplets by mechanical spinning (centrifugal) action —rather than hydraulic pressure or air shear. On the other hand, conventional spray nozzles produce droplets that vary widely, ranging from small droplets that may drift or evaporate before reaching the target to large droplets that concentrate too much pesticide in one spot. The key to CDA technology is a rotary spray nozzle that creates a consistent droplet size and uniform pattern width.
Droplet Size Classification
Droplet-size information helps determine 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 (Table 26.5). This system enables the comparison of droplet sizes between various nozzles, operating conditions (pressure), and manufacturers. Nozzle manufacturers utilize these standardized systems to indicate the droplet size of their nozzles for multiple sizes and pressure combinations, and pesticide companies use these classification systems to recommend appropriate droplet sizes for use with their products.
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