Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 13, 1999
Publication Date: N/A
Interpretive Summary: Pesticide applicators should be familiar with spray quality and what it means relative to compliance with crop protection product labels. Some existing and many new and reregistered product labels will require application with a specific spray quality such as Medium or Coarse. Applicators of pesticides with these labels will need to know how to achieve the specified spray quality with their application. Spray nozzle orifice size, deflection angle, pressure, and airspeed are primary factors that determine spray quality. Computer spreadsheet models were developed that will permit aerial applicators to input these factors for an application; then the model will estimate the resulting spray quality. Straight stream nozzles may be used to produce larger or more-coarse spray droplet sizes that are less likely to drift from the application site. These spreadsheet models are available on diskettes and web pages for applicator use. Models for three straight stream nozzles and some other common nozzles are available. Use of these models will permit operators to comply with crop protection label requirements for applying sprays with a specific spray quality.
Technical Abstract: Industry and government agencies are working together to help applicators of crop production and protection products reduce incidents of damaging spray drift. One of the more recent approaches has been to include information on product labels that help applicators select spray nozzle operating parameters that will reduce spray drift. The general term used on labels to describe sprays is spray quality. Spray quality is further characterized by definitions of droplet size spectrum ranging from very fine to extra coarse. These definitions are specific; for example, sprays with volume median diameter less than 120 um will be classified as very fine. Ground spray applicators can obtain spray quality data for various nozzles from color-coded charts available from nozzle manufacturers. Determining spray quality from aerial applications is more complex because of the additional atomization from air shear due to aircraft speed. Aerial applicators have long been familiar with the fact that small droplets are more prone to drift than large droplets, but information on the spray droplet size from a given set of aerial application conditions has not been easy to assess. Aerial applicators also know that straight stream nozzles produce larger droplet spectrums that are less prone to drift. Several options on aerial straight stream nozzles are available. Spreadsheet models were developed for aerial straight stream nozzles that could be used by aerial applicators to assess spray quality and comply with product labels.