Optimising pesticide use in arable agriculture by improving nozzle selection based on product efficacy to give optimised use and improved spray drift control

Abstract

This project aimed at developing an extended spray/nozzle classification scheme that could accommodate a wider range of nozzle designs than existing schemes and particularly including air-induction nozzles. The extended scheme would have components relating to possible product efficacy and the risk of spray drift as separate elements. The work was based on an initial hypothesis that had two components:
1) there is a negative correlation between product efficacy and deposit variability, so that data relating to deposit variability measured according to specific protocols could be used in an extended classification scheme; and 
2) a spray drift risk parameter could be obtained from comparative spray drift measurements made to defined protocols in wind tunnel or field conditions.

Measurements of spray deposits on stainless steel rods in laboratory conditions showed that the highest levels of variability were associated with nozzles and application variables that gave good levels of efficacy when treating the main arable crops with boom sprayers, and therefore the first components of the initial hypothesis, were rejected. Further measurements with a wide range of nozzle designs gave deposit/droplet size relationships that indicated the potential for an efficacy classification based on deposit quantity, but the resolution and experimental repeatability were not sufficient to enable a revised classification approach to be defined at this stage. However, the work did deliver:
• results that supported the approach taken in the AHDB Cereals & Oilseeds Nozzle Guide including considering air-induction nozzles as either “small droplet” or “large droplet”;
• evidence that factors other than droplet size (particularly droplet velocity) are important in determining deposit on targets and could, therefore, be the basis for future work in developing classification systems;
• a specification for a revised test liquid for use in nozzle testing and spray application experiments that did not use a nonylphenol surfactant;
• data to show that application volumes of 75 to 100 L/ha gave deposits on small
• approaches that would enable a component of drift risk assessment to be included in an extended classification scheme.