Chapter 25

Pesticide Application and Equipment in Greenhouses

Sprayer Nozzles

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.

Nozzle Materials

Nozzles are made from several materials. The most common are brass, nylon, stainless steel, hardened-stainless steel, tungsten carbide, thermoplastic, and ceramic. There are advantages and disadvantages with each type of material. Brass nozzles are relatively inexpensive, but they wear rapidly with abrasive materials, such as wettable powders and liquid fertilizers. Stainless steel and hardened stainless steel are the most resistant to wear, but their expense discourages some users. Frequent replacement of brass nozzles usually makes their use more costly in relation to the area sprayed.

Nozzle Types

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. There are different types of spray patterns produced by nozzles each designed for a specific application. Choosing the proper nozzle for a particular treatment will ensure good coverage and minimum drift. The selection of a nozzle is determined by the type of treatment being applied as well as certain aspects of the spray equipment such as flow rate and operating pressure. Herbicides are applied at low pressure to produce large droplets that reduce drift. Higher pressures are used with fungicides to produce small droplets for better coverage of foliage. Insecticides are applied with pressure ranges between these two extremes. Drift control adjuvants work best with nozzles that reduce the number of fine and mist-like drops. To be effective and safe, nozzles may need to be changed for different pesticide applications. The different types of fan nozzles are designed to work only within certain pressure ranges. Even slight changes in spray pressure will alter the pattern produced by a fan nozzle. It is also important that the nozzles are at the proper height above the target. Otherwise the spray pattern will not provide uniform coverage. The required height depends on the nozzle angle and spacing along the boom. Refer to manufacturer charts for the correct spacing, height, and pressures for various fan nozzles. Spray nozzles fall into three basic categories:

  • Hydraulic nozzles
  • Air-shear nozzles
  • Controlled droplet applicators

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 large 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. The advantages and disadvantages of hydraulic nozzles are:

Cone Nozzles

Cone nozzles are used primarily when plant foliage penetration is essential for effective insect or disease control and when drift is not a major concern. At pressures of 40 to 80 psi, these nozzles produce small droplets that readily penetrate plant canopies and cover the underside of the leaves more effectively than any other nozzle type. However, because of the small droplets produced and high operating pressures, these nozzles produce patterns which are very susceptible to drift and generally not recommended for broadcasting herbicides. The two common styles of cone nozzles available are the solid-cone and hollow-cone.

Flat-Fan Nozzles

Flat-fan nozzles are widely used for broadcast spraying of herbicides and some insecticides. They produce a tapered-edge, flat-fan spray pattern. Less material is applied along the edges of the spray pattern, so the patterns of adjoining nozzles must be overlapped to give uniform coverage over the length of the boom. Normal operating pressure is variable depending on the nozzle used. Lower pressures produce larger droplets, which reduces drift potential, while higher pressures produce small drops for maximum plant coverage, but small drops are more susceptible to drift. Flat-fan nozzles are available in several spray discharge angles. Proper spray boom height depends on nozzle discharge angle and is measured from the target to the nozzle. These nozzles have several subtypes, such as standard flat-fan, even flat-fan, low pressure flat-fan, extended-range flat-fan, and some special types such as off-center flat-fans, and twin-orifice flat-fans.

Turbulence Chamber Nozzles

Recent designs in nozzles have added the use of a turbulence chamber to further absorb energy within the tip and increase droplet size. This not only creates larger droplets but alos improves the uniformity of the spray pattern. Examples include Turbo Teejet (Spraying Systems Co.) in a small, flat-fan tip design and Turbo Floodjet in a flooding tip design.

Air-Induction Nozzles

Air induction (AI), (commonly referred to as air inclusion or venturi) nozzles have the same basic design feature—two orifices, one to meter liquid flow, and the other larger orifice to form the pattern. Between these two orifices is a venturi or air aspirator, used to draw air into the nozzle body. In the body, air mixes with the liquid forming an air-entrained spray pattern at a lower pressure. The spray pattern is comprised of large, air-filled, coarse droplets with very few drift-susceptible droplets.

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 but if discharged at 90 degrees to the air-stream the droplets are larger, and even larger if discharged with the air flow. Faster airblasts produce smaller droplets. An increase in the liquid flow rate or a reduction in airblast causes the formation of larger droplets, while decreasing the liquid flow or increasing the air flow produces smaller 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 with a narrow range of droplets of the same size. 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. As there are no large or small droplets in the CDA spectrum, all the droplets stick to the plants and so reduced rates can be applied.

Droplet Size Classification

Droplet-size information is useful for determining the correct nozzle for a pesticide application. To help applicators select nozzles appropriate for particular agricultural chemicals and circumstances, international standards have been developed to define spray quality in a more practical way. A classification system developed by the British Crop Protection Council (BCPC) and the American Society of Agricultural and Biological Engineers (ASABE) standard S572.1 assigns a droplet-size category to a nozzle based on droplet-size spectrum (See Table 25.2). Five categories of spray quality were devised: very fine, fine, medium, coarse and very coarse. This system allows for comparison of droplet size between various nozzles, operating conditions (pressure), and manufacturers.

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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