Nozzle selection: making the right choice for paraquat

Which nozzles to use?Choosing the correct type of nozzle when spraying paraquat is an important decision. The right nozzle will enable the best levels of weed control, helping to ensure that the product is used accurately and efficiently, avoiding spray drift onto non-target areas. Many different types of nozzles are available for various crop protection purposes, being suitable for particular products and spray application equipment. While the product label should always be consulted and advice taken locally on which nozzles to use in specific weed control situations, some basic principles of nozzle selection are outlined in this article.

Nozzle functions

Essentially, nozzles comprise an outer case holding a chamber into which the spray solution is pumped at a designated pressure and leaves through a specially shaped orifice in the nozzle tip. Nozzles fix onto the spray boom at regular intervals along its length, or onto the end of a hand-held lance. They deliver the spray solution as thin sheet of liquid, of a certain shape, which breaks into droplets. The average size of droplets is determined by the pressure and nozzle type. Crop protection products are recommended to be applied at certain rates per unit area in a certain volume of water, e.g. 2 L/ha in 200 L water/ha. The water volume is recommended according to the coverage of the target area required for best effect. This is determined by factors such as the location of the actual target weed, pest or disease in the crop; and whether the product has contact or systemic activity. At a given pressure, a particular nozzle type will deliver a certain flow of spray (volume per minute). The forward speed of the sprayer and the swath width then determine the rate of product applied. Appropriate nozzle types must be selected according to the particular targets, products used, application methods and prevailing weather conditions. Using nozzles producing larger droplets reduces drift potential, but will not prevent drift if applications are not made properly (e.g. boom held too high) or the weather is unsuitable. Low humidity encourages the evaporation of droplets, reducing their size and wind blows fine droplets off-target.

Nozzle types

The main basic types of spray nozzles and their principle features and uses are described in the table below. 
Nozzle tip type  Main features and uses
Flat fan Produces a flat fan shaped output of medium to larger droplets for broadcast* application of herbicides, avoiding spray drift.
Deflector  Used with knapsack sprayers for herbicide application; spray is directed downwards from the end of a lance.
Cone (hollow or full) Produces a cone shaped output; used with high spray pressures where penetration of a crop canopy is needed; for fungicides and insecticides; risk of drift.
Air inclusion** Air is incorporated creating large droplets, which reduces drift; these shatter into smaller droplets when they impact on leaves.
Flood  Produce large droplets; used for high volume application of liquid fertilizers (into which herbicides may be mixed).
* A broadcast application gives full coverage as opposed to spraying bands, or making spot applications.
** Air inclusion nozzles are also known as twin-fluid nozzles.
  Nozzles within the categories shown above are further described by the angle of the spray pattern they produce, use pressure and flow rate. Care should be taken to ensure that nozzles are not blocked, damaged or worn. A check should always be made that each tip is delivering the same volume of spray in the expected even pattern. Blockages should be removed by using compressed air or a soft-bristled brush.

Nozzles for boom sprayers

Standard flat fan nozzles are the best choice for spraying broadcast applications of paraquat products using a boom sprayer. These nozzles produce a fan-shaped, flat oval spray pattern, requiring overlap to produce even coverage. Many variants of flat fan nozzles are available: for operating at different pressures; producing larger droplets; giving an even spray pattern not requiring overlap for band spraying.  They come with tips giving spray fans with a range of angles. Wider angles are needed to give the overlap necessary for even coverage when the spray boom is held at a lower height.

Nozzles for knapsack sprayers

Knapsack sprayer application of paraquat using a deflector nozzleDeflector nozzles are most commonly recommended for use on knapsack sprayers, especially for herbicides. The pressurised spray liquid strikes an angled surface in the nozzle to form the spray sheet that produces the drops in the particular pattern of spray fan. They are used to apply wider swaths, and can be used at low nozzle heights such as under trees or bushes. A low operating pressure of 1 bar (14.5 psi) tends to produce coarse droplets which are less prone to drift, reducing off-target contamination. When the operating pressure is raised to 1.5–2.0 bar, these nozzles will tend to produce a medium quality spray. When spraying between rows of, e.g. maize or vegetables, a nozzle shield can be used to confine the spray to the target weeds. More basic information about how to apply paraquat herbicides most effectively, efficiently and safely can be found here. More information about the stewardship

Description

The responsible and ethical management of a crop protection product in a way that takes full and balanced account of the interests of users, future generations, and other species.

Authoritative On-line References and Resources

http://www.croplife.org/ CropLife International is a global federation representing the plant science industry and a network of regional and national associations in 91 countries. These organisations are committed to sustainable agriculture through innovative research and technology in the areas of crop protection, non-agricultural pest control, seeds and plant biotechnology.
of paraquat products can be found here.

Important Note: Always read and follow the product label and adhere strictly to the approved uses.

 

References

Jones, W J (2006). Selecting nozzles for hand-held applications. UK Forestry Commission Technical Note. Johnson, M P and Swetnam, L D (1992). Sprayer nozzles: selection and calibration. University of Kentucky Cooperative Extension Service. Sumner, P E (2005). Sprayer nozzle selection. University of Georgia Cooperative Extension Services.

Notes

The brand name of the leading paraquat product is Gramoxone.